Written by Glicy Lou D. Garinggo
No matter how complex your body is, it is only composed of four basic tissue types. These are epithelial, connective, muscular, and nervous tissue.
They make up cells and molecules from the extracellular matrix, but they don’t exist on their own. They work together and in different amounts to form other organs and systems in the body. They are also critical cells because they help the body do its job.
Epithelial tissues are polyhedral layers that are enclosed together. These tissues have very little extracellular material. These tissues stick together very well. They form sheets that cover the body’s surface and line its cavities.
The main functions of epithelial tissues are:
- Covering, lining, and protecting surfaces (e.g., skin)
- Absorbing (e.g., the intestines)
- Secreting (e.g., the epithelial glands)
- Contractility (e.g., myoepithelial glands)
There are some cells in some epithelia that are very good at sensing. These can be like those in the tongue or your nose lining. Everything has to go through an epithelial sheet to get into or leave the body.
How many types of epithelial tissue are there?
We can break Epithelia into two main groups based on their structure and function.
The covering (or lining) epithelial and glandular epithelia.
Covering or Lining Epithelia
It’s called a “covering” because the cells arrange themselves in layers. They cover the outside of the body or line the inside of it. You classify them by how many layers of cells there are and how the cells in the surface layer look. Simple epithelia have only one layer of cells. Stratified epithelia contain more than one layer.
You also base the shape of the cells that make up simple epithelia. They can be squamous (or thin cells), cuboidal(cube-like), or columnar (cells taller than they are wide).
Simple Squamous Epithelium
In simple squamous epithelium, this is in a single layer. The cells of the single-layer is flat and usually very thin. Only the thicker cell nucleus shows up as a bump to show that the cell is there. You can find simple epithelia on the inside of blood vessels.
You can also find them in other areas where substances can get into the rest of the body. They keep substances from getting into the rest of the body. Often, thin cells have transcytosis.
Simple Cuboidal epithelium
Cells in simple cuboidal epithelia can be tall or short. They’re the same height and width, but not always. Their thicker cytoplasm often has a lot of mitochondria in it. Having many powerhouses gives them a lot of energy to move things across the epithelia.
Simple Columnar Epithelium
Cells in simple columnar epithelia are taller than wide and denser. These cells are very good at absorbing. They have microvilli and mix with secretory cells or ciliated cells.
Those epithelial cells always have tight and firm junctions at their top ends. But they are often linked in the more basolateral parts of their bodies. This structure allows for rapid transfer to the space between the cells instead of moving across the cells.
Columnar cells have more cytoplasm. They tend to have more mitochondria and other organelles for absorption and processing. Examples include a renal collecting duct, the oviduct, and the gall bladder. They all have secretory and ciliated cells, like the oviduct and gall bladder.
We can also divide stratified epithelia into four groups. Again, by basing on the cell shape of the surface layer. These are squamous, cuboidal, columnar, and transitional.
We can call the fragile cell surface cells “nonkeratinized” or “keratinized.” Try to look at your skin and see a stratified squamous keratinized epithelium. Many cells form layers, and the cells near the connective tissue are usually low columnar or cuboidal.
The cells flatten and become irregular in shape as they build up keratin during keratinization. As they move closer to the surface, they become thin. They also got inactive packets of keratin without a nucleus.
Cells on this epithelia’s surface help keep water from leaking across it. Wet cavities have stratified, squamous, or nonkeratinized epithelia like the mouth, esophagus, and vagina.
In these areas where water loss is not a problem, the cells have much less keratin and still have nuclei.
Stratified Squamous Epithelium
Stratified squamous epithelia protect the underlying tissue from microorganisms and water loss. Protection against water loss and drying out is essential for the skin. The epithelia have keratin which means it is hard.
In time, epidermal cells of the skin become filled with keratin and other substances. Still, they also get rid of their nuclei and other parts of their bodies.
Flattened ‘squames’ on the surface form a layer that slows down water loss. They fall off and are replaced. Nonkeratinized epithelial linings are visible on many internal surfaces. Examples of these are the esophagus and the cornea.
This surface is because the differentiating cells have less keratin and keep their nuclei. Because water loss is less of a problem with these epithelia, they don’t need keratin.
Stratified Cuboidal and Stratified Columnar Epithelia
A layer of cells called stratified cuboidal or columnar epithelia isn’t pervasive. Still, you can find them in the excretory tubes of some glands. The double layer of cells makes the lining more durable than a simple epithelium.
Most epithelia are not layered cuboidal or layered columnar cells. We can find it in the conjunctiva, which lines the eyelids. It is both protective and mucus-secreting. Large excretory ducts of sweat and salivary glands only have stratified cuboidal epithelia. This type of tissue is stronger than the simple epithelium.
There are two types of cells in the transitional or urothelium:
Dome-shaped cells that are neither squamous nor columnar. You can see this type of cell only in the bladder, the ureter, and the upper part of the urethra. These cells, sometimes called umbrella cells, protect the body from urine. It is too acidic and could kill cells.
Transitional epithelium or urothelium
The stratified transitional epithelium lines of the urinary bladder have rounded or dome-shaped cells with two unusual features. There are membranes on the surface of the cells.
They can withstand the hypertonic effects of urine and protect the cells below from this toxic solution. Also, the transitional epithelium can change their structure as the bladder fills and the wall stretches.
This action makes the transitional epithelium of a full bladder seem to have fewer cell layers than an empty bladder. It’s called pseudostratified columnar epithelium because all cells attach to the basal lamina.
Their nuclei are at different epithelial levels, and some cells’ height doesn’t reach the surface. This type is also called the stratified columnar epithelium.
Most people know that pseudostratified columnar epithelium lines the upper respiratory tract. This arrangement also has a lot of columnar cells that are very ciliated.
As the cells move, they appear to be in layers. But, the basal ends of these layers are all in contact with the basement membrane, which can be very thick in these epithelia. The best example of this type is the pseudostratified ciliated columnar epithelium of the upper respiratory tract. It has cell types with nuclei at different levels, making it look like cells piled.
Glandular epithelia are cells specialized to secrete. The molecules to secrete are in the cells in small membrane-bound vesicles called secretory granules.
Glandular epithelia may synthesize, store, and secrete proteins (e.g., in the pancreas), lipids (e.g., adrenal, sebaceous glands), or complexes of carbohydrates and proteins (e.g., salivary glands).
Mammary glands secrete all three substances. The cells of some glands have low synthetic activity (e.g., sweat glands) and secrete mostly water and electrolytes transferred into the gland from the blood.
The epithelia that form glands can be according to various criteria. Unicellular glands consist of large isolated secretory cells, and multicellular glands have clusters of cells. We use the term “gland” to designate large aggregates of secretory epithelial cells, such as salivary glands and the pancreas.
What epithelium is skin?
It is keratinized stratified squamous epithelium. It is the source of benign and malignant epidermal tumors found on the skin’s surface.
What is squamous epithelium?
The squamous epithelium consists of flat epithelial layers and looks like scales. The layers are more extensive than tall and look like polygons when seen from the top. It gives a smooth, low- friction surface, making it easy for fluids to move over.
Which epithelium is present in the tongue?
Like on the skin, the squamous epithelium layers on top of the connective tissue, or lamina propria, and the tongue’s muscles. This layer is the basal layer.
Epithelial tissues that are subject to friction, like the covering of the skin or tongue, are where they happen the most.
Which epithelium is present in the kidney?
Glands and kidney tubules have simple cuboidal epithelium, the same type found in both.
Which epithelium is present in the urinary bladder?
Lining epithelium: The urinary bladder lining is the urothelium, a type of stratified epithelia. You can find these body parts only in urinary structures like the ureter, urinary bladder, and proximal urethra.
The urothelium has three layers:
Innermost or apical layer: The innermost layer acts as a barrier between the bladder and other tissues below it. A single layer of umbrella-shaped layers (called umbrella cells) breaks down into two. They form an impenetrable barrier. Tight junctions between the cells and a layer of uroplakin, a glycoprotein, form a plaque on the surface that covers the umbrella layers.
Intermediate Layer: It comprises two to three layers of polygonal layers.
Basal Layer: It has two or three layers of small cuboidal layers. At rest, the urothelium is five to seven layers thick. When the bladder is full of urine, its wall expands to fit the extra space. It doesn’t hurt the bladder when the urothelium reorganizes into two or three layers in a distended bladder. Because the urothelium can move from one place to another, it is also called the transitional epithelia.
Which type of epithelium is in the respiratory tract?
The respiratory epithelium is a ciliated pseudostratified columnar epithelium covering most of the respiratory tract. You can’t find it in the larynx or pharynx, but it covers most of the respiratory tract.
Some epithelial layers are more likely to grow abnormally. This abnormal growth leads to cancer which we call neoplasia. Neoplastic growth has cured and does not always lead to cancer.
Metaplasia is another reversible process in which one type of epithelial tissue changes into another.
The ciliated pseudostratified epithelia that line the bronchi can become the stratified squamous epithelia in many people who smoke. In people who have a long-term lack of vitamin A, epithelial tissues like those found in the bronchi and urinary bladder become stratified squamous epithelia.
Metaplasia is not only found in epithelial tissue. It can also happen in connective tissue.
Mescher, A. L., & Junqueira, L. C. U. (2016). Junqueira’s basic histology: Text and atlas (Fourteenth edition.). New York: McGraw-Hill Education.
Mescher, A. L., & Junqueira, L. C. U. (2016). Junqueira’s basic histology: Text and atlas (Twelfth edition.). New York: McGraw-Hill Education.
Microbiologynote (n.d.) Epithelial Tissue Definition, Characteristics, Types, and Functions. Date retrieved March 31, 2022 from https://microbiologynote.com/epithelial-tissue/
Biology online (2001). Squamous Epithelium. Date retrieved April 1, 2022 from https://www.biologyonline.com/dictionary/squamous-epithelium
National Library of Medicine (2018). Tongue and Taste Organ Biology and Function: Homeostasis
Maintained by Hedgehog Signaling. Date retrieved April 1, 2022 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5966821/#:~:text=Similar%20to%20the
NCBI (2022). History, Bladder. Date retrieved April 1, 2022 from
University of Thi-Qar (n.d.) Glandular Epithelia. Date retrieved April 2, 2022 from https://med.utq.edu.iq/wp-content/uploads/sites/7/2020/09/histology-lecture- 3.pdf
Written by Ayessa G. Ibañez
Genetic material is the hereditary substance holding all information specific to an organism. DNA (deoxyribonucleic acid) is the best example and most common. Although it is present in humans and almost all organisms, DNA is not the only genetic substance.
Considering the definition mentioned, the genetic substance can be a gene, a part of a gene, and a group of genes. Genes are the functional units of inheritance. It contains the data needed to specify traits that pass from parents to offspring.
Moreover, the hereditary substance can be a DNA or RNA molecule, its fragment, and a group of DNA or RNA molecules. You can even include the entire genome of an organism.
They all are raw cellular materials of inheritance. They influence all aspects of the structure and function of an organism.
Deoxyribonucleic acid is the hereditary substance we humans have. Most of them are in the cell nucleus but can also be in the mitochondria. The information in DNA is in the form of code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).
Another type of hereditary substance is RNA or ribonucleic acid. We are not referring to the RNA present in our bodies. What is present in humans work as enzymes in protein synthesis, not as a hereditary substance.
The hereditary substance we refer to works in RNA viruses. It can be either single-stranded (ssRNA) or double-stranded (dsRNA).
There is also another form of inheritance material found in bacteria. Discrete, circular, and supercoiled, they are in the exterior chromosomes of certain bacteria. We call them plasmids.
Plasmids carry information encoding for non-essential characteristics like antibiotic resistance and toxins production. They are independent when replicating from the cell.
There are also conjugative plasmids that are extra-chromosomal deoxyribonucleic acid elements. They can transfer among bacteria making new features in the bacterial cell.
Although these are genetic information, most would prefer DNA as the main one. It is the molecule that fulfills the specific properties of hereditable material.
How do you identify genetic material?
There was a hypothesis stating that RNA stored genetic information in primitive cells. Some studies would say that RNA is the first hereditable material.
As already mentioned, most literature considers deoxyribonucleic acid as a genetic substance. But, before it was even deemed one, some geneticists found the hypothesis absurd. This is due to chromosomes, the carriers of the genetic material, having both DNA and protein.
The idea prompted scientists in the early 1900s to conduct experiments to prove it. The foundation of their studies relies on four criteria to identify genetic information. These are information, replication, stability, and mutation.
The function of living things is dependent on the data provided by the genetic substance. Thus, it must have the information necessary to construct an entire organism. It must provide the blueprint to determine the inherited traits of an organism.
“A genetic material must carry out two jobs: duplicate itself and control the development of… the cell…,” quoted by Francis Crick.
Replication refers to the duplication of its genetic substance by consistent replication. The process is by duplicating the nucleic acid molecule.
This concept is familiar to most due to DNA replication. It is a rule before cell division, guaranteeing that each daughter cell has a copy of the genome.
This criterion is vital as hereditable substance passes down from parents to offspring.
A genetic substance must be stable. Its structure is not easy to alter with the changing stages of life and the age of physiology of living beings.
For example, DNA can survive in heat-killed bacteria. Both the strands of deoxyribonucleic acid, which are complementary, can separate.
The hereditary stability depends on an accurate DNA replication system. It also relies on the success at various levels of DNA repair systems in the cells.
Mutations are crucial to evolution.
A genetic substance must have the capacity to cope with slow changes or mutations to evolve. Such change from mutation must inherit with stability.
Every new DNA sequence is due to a particular gene created from a new allele. Thus, every feature an individual has is a result of mutation.
What is another name for genetic material?
As already discussed, DNA is the raw material of inheritance of almost all living things. Another name that can also stand for genetic substance is a gene, the basic unit of heredity.
Genes are a small section of deoxyribonucleic acid. They are biochemical instructions within the genome that code for proteins. These proteins, in turn, impart or control the characteristics that create our individuality.
The role of genes is crucial as they store information.
The complete set of genetic instructions characteristic of an organism is the genome. It includes the protein-encoding genes and other DNA sequences.
The protein-encoding gene can vary in base sequence from person to person. The different forms of genes are the alleles.
Alleles with particular genes are in pairs, placed one on each chromosome. The combination of alleles influences an individual’s observable traits or phenotype.
Same alleles with a particular gene are homozygous. An individual will inherit the same alleles for a particular gene from both parents. For example, assume the gene of skin color has identical color alleles on the pairs.
Different alleles are heterozygous for that gene. The gene of hair color has two alleles, one code for white (R) and the other code for black (r).
A gene can mutate, causing changes in the DNA sequence that distinguish alleles. The change from the mutation passes on during cell division of the cell it contains.
If the change is in a sperm or egg cell that becomes a fertilized egg, it passes to the next generation.
What are the characteristics of genetic material?
An information carrier is not enough character to describe a hereditary substance. Several attributes a genetic material owns make it apart from others.
Below are the properties and functions that define the genetic substance.
- It is present in every cell.
2. It contains all the necessary biological information.
3. It is stable both in chemical and physical aspects.
4. It can store information in coded form.
5. It has control of the biological functions of cells.
6. It expresses its information in the form of Mendelian characters.
7. It is the same both in quantity and quality in all the somatic cells.
8. It presents diversity corresponding to the variety existing in the organisms.
9. Its replication is precise and passes over its true copies to the next generation.
10. It is capable of variations, for instance, mutation. The variations are stable and inheritable.
11. It can generate its own kind and new kinds of molecules.
12. It is capable of differential expressions. This factor allows diversity despite the same genetic information.
How is genetic material inherited?
We get most of our features from our parents, either our mom or dad or even our grandparents. Your body physique is from your dad, or you got your curly hair from your mom. Sometimes, you even wish you got your mother’s hazelnut eyes which you did not because you got your dad’s.
The similarity of the characteristics within your family is because of inheritance.
The concept of inheritance is somehow like the terminology used in finance. You pass down an asset to a particular individual or individual. But, in genetics, what you will pass down is your genetic information, an intangible asset we all have.
Inheritance is the transmission of traits from one generation to the next.
A deoxyribonucleic acid molecule comprises a chromosome. These chromosomes are in the nuclei of all human cells, excluding mature red blood cells. In every cell, there are 23 chromosomes of different pairs.
In sexual reproduction, the egg and sperm cells combine to form the first cell of a new organism. This process refers to fertilization.
The fertilized egg carries two sets of 23 chromosomes. We call this a diploid cell, meaning it has paired chromosomes, one from each parent. In total, the cell has 46 chromosomes.
The data within your parents’ chromosomes have a copy of the new cells made during cell division. The fertilized egg now has the complete set of instructions needed to make more cells.
The inheritance of hereditary substances is evident in the characteristics your family has. Heritage is not limited to physical traits, but diseases can be also passed down.
There are instances of genetic mutation, and the parents can also pass it down to their children. This is why some members can get the diseases that run in families.
Why is deoxyribose called deoxyribose?
Deoxyribose or 2-deoxyribose is the DNA’s sugar. It is a pentose sugar with five carbon atoms connected to each other to form a ring-like shape.
Its five-sided ring-like structure consists of four carbons. The fifth carbon is in the ring, which is branching off.
The structure of deoxyribose coins the name itself.
The pentagon shape of the molecule has 1′-4′ starting at the carbon at the right side of the oxygen. The numbering of carbon moves in a clockwise direction.
The numbers have the upper-right stroke mark (‘). They are not written in plain numbers because the mark indicates that it is a prime. A prime denotes carbon atoms in sugar from the carbon and nitrogen atoms in the nitrogenous base.
The term for the sugar of DNA is deoxyribose because it does not have a hydroxyl group at the 2′ position. Instead, it has hydrogen.
There is a change in the standard ribose form, causing replacement on the hydroxyl group (–OH) of 2′ carbon. A hydrogen group (–H) replaces the hydroxyl group (–OH).
What is the backbone of DNA?
The DNA molecule is a polymer of long, chainlike molecules of monomers. Monomers are subunits of a larger polymer chain. In deoxyribonucleic acid, the repeating structural unit is the nucleotides.
Nucleotides are the basic unit of deoxyribose acid. In the body, they are part of the components of nucleic acids or work as individual molecules.
The nucleotide is a complex molecule made up of three distinct components. These are sugar, a nitrogenous base, and a phosphate group.
Phosphate groups are a set of specific atoms of phosphorus. They are identical across all nucleotides.
As for the sugar, the component is exactly what it sounds like—the usual sugar, like the ones which are part of our diets. Nucleotides may contain one of the various types of sugar molecules. For deoxyribonucleic acid, the sugar found in the nucleotides is pentose.
From its root word pent-, a pentose is a sugar that comprises five carbon atoms. The certain type of pentose present in the nucleotides found in DNA is 2’-deoxyribose.
Pentose sugars can be in two forms. It can be straight-chain, or Fischer structure; and the ring, or Haworth structure. In DNA, it is the ring form of 2’-deoxyribose that is present in the nucleotide.
Nucleotides join into long chains between the deoxyribose sugars and the phosphates. This creates a continuous sugar-phosphate backbone.
Hence, the backbone of a DNA strand consists of a phosphate group and a pentose sugar, deoxyribose.
Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. The RNA World and the Origins of Life. Available from: https://www.ncbi.nlm.nih.gov/books/NBK26876/
Ancestry (n.d.) DNA Structure. Retrieved from https://www.ancestry.com/lp/dna-structure
Ancestry (n.d.) What Is DNA’s Sugar? Retrieved from https://www.ancestry.com/lp/what-is-dna-made-of/dna-sugar#:~:text=The%20carbons%20in%20 the%20pentagon,group%20at%20the%202’%20position.
Biology Online Editors. (2022). Genetic material. Retrieved from https://www.biologyonline.com/dictionary/genetic-material.
Bhagavan, N. & Ha, C. (2015). Chapter 22 – DNA Replication, Repair, and Mutagenesis. Essentials of Medical Biochemistry (Second Edition) With Clinical Cases 2015, Pages 401-417. https://doi.org/10.1016/B978-0-12-416687-5.00022-1.
Brown, T. (2012). Introduction to Genetics: A Molecular Approach. Garland Science, Taylor & Francis Group, LLC. ISBN 978-0-8153-6509-9
BYJU. (n.d.). Genetic Material- DNA vs RNA. Retrieved from https://byjus.com/biology/genetic-material-dna-rna/.
Carlin, J. L. (2011) Mutations Are the Raw Materials of Evolution. Nature Education Knowledge 3(10):10
Collins, F. (n.d.). Gene. Retrieved from https://www.genome.gov/genetics-glossary/Gene.
Genetic Material: Definition, Structure & Function. (2016). Retrieved fromhttps://study.com/academy/lesson/genetic-material-definition-structure-function.html.
Genetic Science Learning Center. (2016) What is Inheritance? Retrieved February from https://learn.genetics.utah.edu/content/basics/inheritance/
John R.McCarrey, J. (2018). Genetic Vs. Epigenetic Inheritance Overview. Encyclopedia of Reproduction (Second Edition) Volume 3, 2018, Pages 434-435.
Kumar, S. (n.d.). Top 8 Characteristics and Properties Genetic Material. Retrieved from https://www.biologydiscussion.com/genetics/genetic-material/top-8-characteristics-and-propertie s-genetic-material/15434
Lewis, R. (2009). Human Genetics: Concepts and Applications. 9th Ed. McGraw−Hill Primis. ISBN−10: 0−39−023244−0
Samiksha, S. (n.d.) Genetic Material: Nature and Properties of Genetic Material. Retrieved from https://www.yourarticlelibrary.com/genetics/genetic-material-nature-and-properties-of-genetic-m aterial/12145
The American Phytopathological Society (n.d.) Mutation. Retrieved from https://www.apsnet.org/edcenter/disimpactmngmnt/topc/PopGenetics/Pages/Mutation.aspx#:~:te xt=Mutation%20is%20important%20as%20the,specific%20gene%20through%20intragenic%20r ecombination.
Viguera E. (2011) Replication (Genetics). In: Gargaud M. et al. (eds) Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-11274-4_1366
Written by Nichole Isabelle J. Fidel
What are DNA and genes? You would often hear that parents pass on their traits and characteristics to their kids. Heredity is the term associated with the passing down of traits from parents to kids. Genetics studies how those traits pass down through the generation.
You need to distinguish both terms to understand how heredity and genetics work. Functional units often make up complex units.
For example, the gene is the primary and functional unit of heredity. Moreover, your DNA makes up your gene. DNA (deoxyribonucleic acid) contains genetic information and instruction about the cell.
Genes consist of portions of DNA. Your genes contain the information required to synthesize proteins. These proteins play a huge part in expressing a trait.
The human body contains around 25,000 to 35,000 genes. Each gene in your body has its own task.
You can find DNA everywhere—in plants, animals, and the human body. Each cell in your body contains DNA. Your DNA is so complex that scientists could not see what it looked like until 60 years ago.
The deoxyribonucleic acid dictates the activities of your cell. It tells how a living thing like you looks and works in simple terms. Your DNA determines your height, the color of your eyes, and other characteristics. It even determines whether you might be at risk of acquiring a disease.
You inherit your DNA from your parents, both your mother and father. DNA is essential since cells can’t function without these minute structures.
DNA, despite its very small size, is a very complex structure. Nucleotides serve as the building blocks of your DNA. This genetic information carrier has the following parts.
- Five-carbon sugar molecule
- Phosphate group
- Nitrogen-containing base
Among these, the nitrogen-containing base is what makes you, you. It is because of the sequence of the base that codes for the traits. You can find the genetic coding among the four nitrogenous bases:
- Adenine (A)
- Thymine (T)
- Cytosine (C) and
- Guanine (G)
These bases pair in a particular way. That is— adenine pairs with thymine and cytosine with guanine. These base pairs repeat themselves in different order along each strand of DNA.
The human DNA alone contains around 3 billion pairs of these nitrogenous bases. The arrangement of the bases is critical. It functions as a code that instructs cells to produce specific types of proteins.
You can think of deoxyribonucleic acid as a ladder. It is a double helix that coils into a spiral staircase form. Nucleotides run up on both sides. Located in the middle are the base pairs held together by hydrogen bonds.
Since these structures are tiny, you need to use an electron microscope to view them.
The healthy functioning of your DNA allows the healthy functioning of your DNA. The synthesis of proteins requires the presence of deoxyribonucleic acid. Also, the reproduction of an organism is dependent on the hereditary material.
Oftentimes, a process referred to as mutations happen. This occurs as a result of errors in the DNA. It is capable of causing sickness and other complications.
Where is DNA located?
You can find DNA in almost all living organisms. But, in the human body, you can find them inside your cells’ nucleus. You can also find DNA in the mitochondrion.
In your body, around 30 trillion cells are present. And inside these cells, most, but not all, contain DNA. Cells such as your red blood cells, hair cells, and nail cells do not have DNA.
A human cell has approximately six picograms (pg) of DNA. It is less than the weight of a grain of rice, which weighs around 29 billion picograms.
Your cells have a nucleus structure, which contains your deoxyribonucleic acid. The DNA found in the nucleus of your cell is nuclear DNA.
DNA is also found in the mitochondria—the cell’s powerhouse. This type of DNA is the mitochondrial DNA or the mtDNA. DNA found in the mitochondria is not linear; it is circular.
Mitochondria (sing. mitochondrion) are structures that convert energy from food. It transforms it into a form that cells can use for their activities.
The nucleus has a crucial role in our cells. It serves as the cell’s command center. It is because it contains the DNA, which carries the genetic instructions for the cell. These instructions are essential for an organism to develop, survive and reproduce.
Inside the nucleus is a thread-like structure called chromosomes. DNA composes each of your chromosomes. Your DNA packs itself several times around proteins called histones.
The histones found in the chromosome helps a chromosome maintain its structure. In order for the long DNA molecules to fit in the cell nucleus, it wraps around the histones. The result would be a compact shape for the chromosome.
Humans have over six feet of DNA distributed across 46 chromosomes.
You can find DNA in the chloroplast in other organisms such as plants and eukaryotic algae. For prokaryotes, such as bacteria, the cytoplasm stores DNA.
According to studies, the DNA of us humans and chimpanzees are 98 to 99 percent identical. But the question of whether two people have the same DNA is unlikely. The DNA of two human beings can only be 99.9 percent similar, but they are not the same.
The majority of our DNA dictates our humanness rather than our uniqueness.
As human species, we have little genetic diversity.
Two unrelated persons have a DNA difference of roughly one in every 1,000 base pairs. But, the human genome has three billion base pairs. Having an average of three million genetic differences between two strangers is small.
SNPs are responsible for the variation in genetics among people. SNP stands for single nucleotide polymorphisms. It occurs when a single letter of the genetic code alters.
The human genome contains an approximate number of 20 million recognized SNPs. It indicates that the odds of two people having the same DNA are equal to having a deck of 20 million cards.
Each SNP denotes a variation in a single DNA building unit known as a nucleotide. You can find SNPs throughout your DNA.
Literature suggests that they occur around once every 1,000 nucleotides on average. According to some studies, a person’s genome has four to five million SNPs.
These variations may be unique or shared by a large number of individuals. Scientists have identified over 100 million SNPs in populations worldwide.
The variations in your DNA serve as biological markers. It assists researchers in identifying genes connected with disease.
When SNPs occur within a gene or a regulatory region next to a gene, they may directly affect the disease. They can do so by changing the function of the gene.
The majority of single nucleotide polymorphisms do not affect your health or development. Yet, some of these genetic differences have been shown to be significant in studying human health.
SNPs are important since it aids in predicting the following:
- aid in predicting an individual’s response to specific treatments
- vulnerability to environmental factors such as pollutants
- risk of developing specific diseases.
Scientists may also use SNPs to trace disease gene inheritance within families.
What is the difference between chromosomes and genes?
Chromosomes are microscopic structures consisting of DNA and protein found inside your cells. Each chromosome contains distinct segments of DNA called genes—the unit of heredity.
Each gene has the instructions or recipe for producing a specific protein. These proteins dictate our growth and the characteristics we inherit from our parents. In simple terms, the proteins produced do the work within your cells and body.
The following factors influence your genes:
- nutrition (diet)
- chemical exposure
- instructions and messages from other genes
You can think of your chromosomes as strings of genes connected with non-coding DNA. The chromosomes which contain your genes are DNA-containing molecules.
You can find your chromosomes inside all the cells in your body except the RBCs. Red blood cells lack a nucleus, and since they lack a nucleus, they lack chromosomes.
When a cell is not dividing, the chromosomes are in their chromatin form. It is also known as the interphase of the cell cycle.
A long, thin strand is what it appears to be in this state. Shorter tubes form as the cell divides, as the strand repeats itself.
The centromere is where the two tubes come together before the separation. P arms are the shorter arms of the tubes. The longer arms are the q arms.
You can find 23 pairs of chromosomes in each of your body cells. It means that you have 46 chromosomes in each body cell.
Where do you get 46 chromosomes? 23 chromosomes from your mother’s egg (ovum) and 23 from your father’s sperm make up your DNA.
When fertilization happens, wherein the sperm and the egg unite, it creates the baby’s first cell. This cell replicates to generate all the infant’s cells. The infant now contains 23 pairs of chromosomes—identical to their parents.
Scientists term the 23rd pair of chromosomes the X/Y pair. The X/Y pairs determine your sex. If you have the XX chromosome, your sex is female. Having an XY chromosome would imply that you are a male.
Tightly coiled DNA makes up each of your chromosomes. If we extend it out, it may resemble beads on a thread. The beads referred to are your genes.
Each of your genes contains instructions for the production of a specific protein. You can find around 20,867 protein-coding genes in the human genome. Between the genes are non-coding DNA segments.
Siblings inherit DNA from their parents. Thus, it is safe to say that they share much of the same DNA with slight variations. The slight variations in the DNA account for the distinct characteristics they have.
The variations in the DNA are due to a process called genetic recombination. It occurs throughout the process of creating sperm and eggs in your body.
Genetic recombination reduces the number of chromosomes in normal cells by half. That is, from 46 to 23 chromosomes. It results in a full genetic bundle when sperm and egg join during conception.
Each child receives half of their DNA from each parent, but this is not always true. Full siblings will share a small amount of their DNA with both parents. On both the mother and father’s strands of DNA, the siblings will match at the same place.
Many causes can lead to changes in our DNA code. These include radiation exposure, chemical exposure, random mutations, and other unknown factors.
We are all unique because of the variations in our genetic code. Even identical twins are born with slight differences in their DNA.
Your DNA is a long molecule that coils itself to form your chromosome. There are roughly 3.1 billion DNA bases in each set of 23 chromosomes. There are around 3.2X10^9 DNA nucleotide pairs in your human genome.
Your cells undergo continuous division to produce new cells as you grow older. During the process of division, your chromosomes become a rod-shaped structure. During the division process, you see your chromosome in a rod-shaped structure.
Specific dyes stain your chromatin. Chromatin is a structure in your chromosome. In testing, the dyes generate distinct banding patterns sorted in size order. A karyotype is the result of this process.
Using these patterns, scientists can determine the size and shape of each
chromosome. Scientists often number the chromosomes in order and size. Autosomes are numbered chromosomes.
How many sexes do humans have?
A human has two sexes—male and female. Your sex chromosomes, the 23rd pair, determine your sex. Women have two X chromosomes in their cells, whereas men have both X and Y.
Egg and sperm cells have an X or Y chromosome, but only egg cells have an X chromosome. That is why when fertilization occurs; the male determines the sex of the offspring.
Having an XX chromosome indicates that you are a female. You are a male if you have XY chromosomes.
Females have 44 autosomal chromosomes in their bodies. According to some sources, they have a karyotype 46, XX. There are fewer chromosomes in eggs than male reproductive cells, making them unique.
Males have a 46, XY karyotype. Because only half of the chromosomes in sperm are present, sperm are distinctive.
The X chromosome is larger than the Y chromosome. It is intriguing since it means that these two chromosomes are distinct. Genetically, they’re also very diverse.
Other creatures share a similar condition, even if their chromosomes have different names.
Biology for Kids: Chromosomes. (n.d.). Ducksters.Com. Retrieved March 25, 2022, from https://www.ducksters.com/science/biology/chromosomes.php
Crow, J. F. (n.d.). Unequal by nature: a geneticist’s perspective on human differences. American Academy of Arts & Sciences. Retrieved March 22, 2022, from https://www.amacad.org/publication/unequal-nature-geneticists-perspective-human-differences
Finegold, D. N. (2022, March 17). Genes and Chromosomes. MSD Manual Consumer Version. Retrieved March 25, 2022, from https://www.msdmanuals.com/home/fundamentals/genetics/genes-and- chromosomes#:%7E:text=Genes%20are%20segments%20of%20deoxyribonucleic,that%20contai n%20a%20person’s%20genes.
Histone. (n.d.). Genome.Gov. Retrieved March 22, 2022, from https://www.genome.gov/genetics- glossary/histone
OpenStaxCollege. (2013, March 6). The Nucleus and DNA Replication – Anatomy & Physiology.
Pressbooks. Retrieved March 22, 2022, from http://pressbooks- dev.oer.hawaii.edu/anatomyandphysiology/chapter/the-nucleus-and-dna- replication/#:%7E:text=The%20nucleus%20houses%20the%20genetic,and%20condenses%20to
Villazon, L. (2020, April 20). Could two people who aren’t twins have the same DNA? BBC Science Focus Magazine. Retrieved March 22, 2022, from https://www.sciencefocus.com/the-human- body/could-two-people-who-arent-twins-have-the-same-dna/
What are single nucleotide polymorphisms (SNPs)?: MedlinePlus Genetics. (n.d.). Medlineplus.Gov.
Retrieved March 22, 2022, from https://medlineplus.gov/genetics/understanding/genomicresearch/snp/
What is a chromosome?: MedlinePlus Genetics. (n.d.). Medlineplus.Gov. Retrieved March 22, 2022, from https://medlineplus.gov/genetics/understanding/basics/chromosome/#:%7E:text=In%20the%20nu cleus%20of%20each,histones%20that%20support%20its%20structure.
What Is a Gene? (for Kids) – Nemours KidsHealth. (n.d.). Genetics.Edu.Au. Retrieved March 25, 2022, from https://kidshealth.org/en/kids/what-is-gene.html
What is DNA?: MedlinePlus Genetics. (n.d.). Medlineplus.Gov. Retrieved March 22, 2022, from https://medlineplus.gov/genetics/understanding/basics/dna/#:%7E:text=Most%20DNA%20is%20 located%20in,form%20that%20cells%20can%20use.
Written by Josh Carl Vince B. Partosa
The human body consists of organs, each having specific functions. Cells are what make tissues, and tissues then form organs. Similarly, cells have organs of their own called organelles. An important organelle is ribosomes. It is important in the synthesis of protein, a molecule needed for growth and metabolism.
The ribosomes produce protein for both inside and outside of the cell. Without these important structures, metabolism and growth would come to a halt.
These structures assemble amino acids to form proteins. They read and follow the molecular instructions found in ribonucleic acid (RNA). This process is what you call translation.
Within the cell, there are two types of ribosomes. These are membrane-bound and free ribosomes.
You can find membrane-bound ribosomes on the rough endoplasmic reticulum (RER). The attached ribosomes are the reason for the RER’s rough appearance, hence, the name.
They are responsible for producing enzymes, a protein important in metabolism. They speed up chemical reactions in the human body. These reactions can be anabolic (grow and build) or catabolic (break down). One example of enzymes produced by bound ribosomes is digestive enzymes. These are the ones that aid in breaking down the food you eat.
To add, these bound structures also make proteins for cell membranes.
In contrast, free ribosomes are not attached to any structure. You can find them free-floating in the cytosol of the cell. They make proteins that constitute part of the cytoplasm which the cell uses.
To understand the importance of ribosomes, you should know the importance of proteins.
Proteins perform several biological functions. Besides growth and metabolism, they also have other roles.
Some proteins are hormones which are chemical messengers. Meanwhile, some transport or store nutrients. Protein (like keratin, collagen, and elastin) also provides structure. They also maintain fluid balance and proper pH across organ systems.
Furthermore, they keep the immune system healthy and are a form of energy source.
Together, these vital functions make protein an important biomolecule of the human body.
How is a ribosome made?
By now, you have learned that ribosomes synthesize protein. But what synthesizes these protein-producing organelles? How are they made? The answer lies within the nucleus. The nucleolus forms a complex of protein and ribosomal RNA (rRNA) into a ribosome.
The ribosomal structure is not bound by a membrane, unlike many organelles. They consist of 2 parts, the large and the small subunits. In eukaryotes, such as in the human body, these subunits contain about half protein and half rRNA.
In ribosome biogenesis, the part of the cell to look at is the nucleus and the cytoplasm.
Within the nucleus is the nucleolus. It is a specific region where the synthesis of ribosomes takes place.
The cytoplasm contains proteins. As discussed before, ribosomes make proteins that are used in and out of the cell. Some proteins present in the cell’s cytoplasm become part of ribosome biogenesis. You call these biomolecules ribosomal proteins.
These ribosomal proteins go to the nucleolus through the nuclear pores. They go to the nucleus because they contain nuclear localization signals(NLS). NLS is part of the protein’s sequence which mediates their transport to the nucleus.
Once the protein reaches the nucleolus, they combine with the ribosomal RNA. This is a type of RNA that combines with proteins to make the ribosome. The DNA sections of some chromosomes encode this.
Together, they assemble a ribosomal subunit. These units then leave the nucleus through the pores. They unite only for protein synthesis in the cytoplasm. When there is no production of protein, the pairs separate into individual units.
How does the genetic code get to a ribosome?
The previous information has established that ribosome makes protein under RNA instruction. This whole process involves 2 important major steps: transcription and translation.
This journey of the genetic code to the said organelle is complex and controlled. Transcription and translation comprise the process of gene expression.
Transcription occurs within the nucleus. This step involves the replication of a gene’s DNA sequence to make an RNA molecule. It occurs in 3 main stages: initiation, elongation, and termination.
1. Initiation occurs when the enzyme RNA polymerase binds to the promoter, a region of a gene. As a result, the DNA unwinds so the enzyme can ‘‘read’’ the bases in the template strand. This is one of the 2 strands of DNA.
2. Elongation is the part where the mRNA strand gets added with nucleotides. The enzyme RNA polymerase will then read the uncoiled strand of DNA. It then proceeds to create the messenger RNA (mRNA) using complementary base pairs.
The resulting mRNA strand is almost identical to the non-template strand. They differ in that RNA has Uracil instead of Thymine in its nucleotide sequence.
3. Termination is the last stage of transcription. It occurs when the RNA polymerase crosses a stop sequence in the gene. As the mRNA strand is complete, it detaches from DNA.
In eukaryotes, there are extra steps such as end modifications and splicing. End modifications increase the stability while splicing provides the correct sequence.
In transcription, the single-stranded genetic material made is mRNA. Its name describes its function. It delivers the message from the DNA in the nucleus into the cytoplasm.
Translation occurs in the cytoplasm. The mRNA exits the nucleus through its membrane’s pores and connects to the ribosome. Each codon or sequence of 3 nucleotides codes for an amino acid, the building block of protein.
Another RNA comes into the picture, and it is the transfer RNA (tRNA). The tRNA recognizes a complementary mRNA calling for its amino acid.
It then binds its anticodon to the codon. An anticodon is a trinucleotide sequence that complements the codon. The usual start codon which begins translation is the AUG sequence.
As the ribosome moves along the mRNA, the growing protein chain gets 1 new amino acid. Each time, this is accompanied by the release of the tRNA into the cytoplasm. This assembly of protein continues till the organelle meets a stop codon. It can be either of the 3 sequences: UAG, UAA, or UGA.
To aid in understanding this whole process, you can view the figure below.
Do ribosomes make DNA?
You have learned that ribosomes make protein. But what other substances do ribosomes make? Does it produce DNA? The answer to this question is “No.” The ribosomes do not make deoxyribonucleic acid.
Ribosomes make a protein or amino acid chains. The building blocks of DNA are nucleotides which make up nucleic acids. Although both amino acids and nucleic acids have “acid” in their names, they are not the same. They are different in structure and function.
Amino acids consist of carboxyl and amino groups. Nucleic acids have sugar, nitrogenous base, and a phosphate group. Amino acids form protein while nucleic acids are genetic material.
Because there is no protein in DNA, you can conclude that ribosomes do not make DNA.
If they do not make DNA, what does?
In DNA synthesis or replication, DNA copies itself. Rather than being “produced,” it is replicated. This is important as the new cell needs to be an accurate and precise replica. Otherwise, it might malfunction.
DNA replication for eukaryotes takes place in the nucleus. It occurs during the Synthesis (S) phase before mitosis and cell division. It is a set of very complex mechanisms.
This process requires enzymes like DNA polymerase, primase, helicase, and topoisomerase.
Recalling what you have read before, ribosomes make proteins. Enzymes are proteins. Thus, you can say that ribosomes are indirectly involved in DNA synthesis.
Do ribosomes make lipids?
Ribosomes do not make DNA. But do they make lipids? The answer to this is the same as the former question. No. They do not make lipids.
To reiterate, they make proteins. Moreover, proteins and lipids are also different in both structure and function. So, what organelle makes lipids?
It is the smooth endoplasmic reticulum (ER). It plays a big role in the synthesis of lipids using enzymes. It produces phospholipids and cholesterol that form the membranes.
The smooth ER also plays a role in steroid hormone production and detoxification.
Are ribosomes eukaryotic or prokaryotic?
Eukaryotes and Prokaryotes have characteristics that make them unique from each other. Are ribosomes found only in prokaryotes or eukaryotes? Both of these types of cells contain ribosomes!
This organelle is in both prokaryotes and eukaryotes. This affirms that the ribosome is a characteristic that evolved early on. It is most likely present in the common progenitor of both cell types.
Although the organelle is present in both, they have their fair share of differences.
By this time, you know that the nucleolus is the site for eukaryotic ribosome biogenesis. In the case of prokaryotes, biogenesis takes place in the cytoplasm.
Prokaryotes have 70S ribosomes while eukaryotes have larger 80S ones. The S refers to the Svedberg unit, a unit for sedimentation rate. This rate is a measure of the time it will take for a particle to sediment from a solution when centrifuged.
Do viruses have ribosomes?
You can find ribosomes in the cells of living organisms. A virus is something that is not alive. It does not have a cell. Thus, it having those organelles would be unlikely. Viruses do not have ribosomes.
Due to their abnormal reproduction capabilities, you may think they are alive. But they are not. They are parasites in the sense that they hijack cells for reproduction.
Without a host cell, they cannot reproduce. Because they lack ribosomes, they cannot make proteins. Hence, they must use the ribosomes of their host cell to translate viral mRNA into viral proteins.
Despite being alive, it is interesting to note that they contain nucleic acids. This may either be DNA or RNA. Nucleic acids, if you recall, are genetic material found in the cell.
Many speculate that viruses are a form of proto life–that they preceded cellular life. But their inability to survive without a host makes it very unlikely to be the case. Some scientists say that viruses began as segments that became parasitic.
9.3 transcription – concepts of biology. OpenStax. (n.d.). Retrieved March 20, 2022.
Craig Freudenrich, P. D. (2020, October 8). How DNA works. HowStuffWorks Science. Retrieved March 20, 2022.
Davidson, M. W. (n.d.). Virus Structure. Molecular expressions cell biology: Virus structure. Retrieved March 20, 2022.
Encyclopædia Britannica, inc. (n.d.). Ribosome. Encyclopædia Britannica. Retrieved March 20, 2022.
Endoplasmic Reticulum (rough and smooth). British Society for Cell Biology. (n.d.). Retrieved March 20, 2022, from https://bscb.org/learning-resources/softcell-e-learning/endoplasmic-reticulum-rough-and-smooth/
Foundation, C. K.-12. (n.d.). 12 foundation. CK. Retrieved March 20, 2022, from https://flexbooks.ck12.org/cbook/ck-12-middle-school-life-science-2.0/section/3.5/primary/lesson/dna-structure-and-replication-ms-ls/
Gray, Carolyn. (2022, March 24). What Are the Benefits of Ribosomes?. sciencing.com. Retrieved from https://sciencing.com/what-are-the-benefits-of-ribosomes-13656686.html
Henderson James (Jim) CleavesII, & author, H. J. J. C. I. I. E. (1970, January 1). Svedberg unit. SpringerLink. Retrieved March 20, 2022, from https://link.springer.com/referenceworkentry/10.1007/978-3-662-44185-5_5249
Khan Academy. (n.d.). Molecular mechanism of DNA replication (article). Khan Academy. Retrieved March 20, 2022, from https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/replication/a/molecular-mechanism-of-dna-replication#:~:text=DNA%20replication%20requires%20other%20enzymes,%2C%20DNA%20ligase%2C%20and%20topoisomerase.
Khan Academy. (n.d.). Nucleus and ribosomes (article). Khan Academy. Retrieved March 20, 2022, from https://www.khanacademy.org/science/biology/structure-of-a-cell/prokaryotic-and-eukaryotic-cells/a/nucleus-and-ribosomes
Khan Academy. (n.d.). Transcription: An overview of DNA transcription (article). Khan Academy. Retrieved March 20, 2022, from https://www.khanacademy.org/science/ap-biology/gene-expression-and-regulation/transcription-and-rna-processing/a/overview-of-transcription
Kumar, V. (2021). Introduction to ribosome factory, origin, and evolution of translation. Emerging Concepts in Ribosome Structure, Biogenesis, and Function, 1–13. https://doi.org/10.1016/b978-0-12-816364-1.00002-0
Libretexts. (2021, February 28). 9.2: Transcription. Biology LibreTexts. Retrieved March 20, 2022, from https://bio.libretexts.org/Courses/Lumen_Learning/Book%3A_Biology_for_Non-Majors_I_(Lumen)/09%3A_DNA_Transcription_and_Translation/9.02%3A_Transcription
Libretexts. (2021, January 3). 4.6A: Ribosomes. Biology LibreTexts. Retrieved March 20, 2022, from https://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Boundless)/4%3A_Cell_Structure_of_Bacteria_Archaea_and_Eukaryotes/4.6%3A_Specialized_Internal_Structures_of_Prokaryotes/4.6A%3A_Ribosomes
Lu, J., Wu, T., Zhang, B., Liu, S., Song, W., Qiao, J., & Ruan, H. (2021). Types of nuclear localization signals and mechanisms of protein import into the nucleus. Cell Communication and Signaling, 19(1). https://doi.org/10.1186/s12964-021-00741-y
Marieb, E. N., & Keller, S. M. (2018). Essentials of human anatomy & physiology. Pearson.
Molecular expressions cell biology: Ribosomes. (n.d.). Retrieved March 20, 2022.
Nave, R. (n.d.). Endoplasmic Reticulum. Retrieved March 20, 2022.
Sturm, N. (n.d.). DNA Synthesis. DNA synthesis. Retrieved March 20, 2022.
U.S. National Library of Medicine. (2021, March 26). How do genes direct the production of proteins?: Medlineplus Genetics. MedlinePlus. Retrieved March 20, 2022.
Walle, G. V. D. (2018, June 20). 9 important functions of protein in your body. Healthline. Retrieved March 20, 2022.
YouTube. (2013). Ribosome biogenesis. YouTube. Retrieved March 20, 2022.
Written by Jay Ryan L. Jacutin
Chromosomes are one feature of the eukaryotic cell residing within the nucleus. Its DNA in plants and animal cells is a thread-like structure compacted in a tight manner. The DNA floats in a freeway across the cell in respect of bacteria.
They comprise DNA wherein its structural support called histones coils the chromosomes. The derivation of the term chromosomes comes from the Greek word chroma (color) and soma (body). It is due to the staining of cell structures with colorful dyes in research.
The binding of the chromosomes and histones yields nucleosomes, aiding gene regulation. Moreover, the nucleosomes coiled up to form chromatin loops, making complete chromosomes.
A chromosome contains 2 short arms, 2 long arms, and a centromere. The short arm’s denotation is ‘p’ while ‘q’ for long arms. The entirety of the structures holds or maintains themselves at the center.
The DNA encompasses the chromosomes has thousands of genes. They served as the basic physical and functional unit of heredity. They develop and maintain cells and carry the genetic information to offspring.
Humans get 2 copies of each, inherited from both parents. Most genes are the same to humanity, but only a few variations. The gene’s variation contributes to distinguishing a person’s physical features.
What are the 23 chromosome pairs?
From a diploid perspective, there are 46 in total in counting chromosomes. From a haploid viewpoint, there are only 23.
For a fact, 22 out of 23 are autosomes, and the remaining pair are sex chromosomes (X and Y). As stated, both parents contribute to one chromosome of each pair for offspring. Female obtains 2 X chromosomes while males have a single X and Y chromosomes.
The genes within are vital for the body’s development, growth, and chemical reactions. Otherwise, abnormalities persist either due to deficiency or excess. Rearrangement of its structure may also be a contributing factor:
Deletions. Missing or deleted segment; deficiency.
Duplications. Duplicated or copied component; excess.
Translocations. Either segment from 2 different or the entire chromosomes attached to another centromere.
Inversions. Discontinuity of the bonded chromosomes turned upside down, inverted. Rings. Discontinuity chromosomes formed circles with or without genetic material loss. Chromosomal abnormalities often occur in cell division:
Mitosis yields to duplication of 2 cells from the original cell. It means a cell containing 46 chromosomes divides and produces 2 identical cells. It happens throughout the body, excluding the reproductive organs.
Meiosis resulted in half number of the chromosomes only instead of the usual total of 46. Unlike mitosis, it occurs now in the reproductive organs creating egg and sperm cells.
Other contributing factors increasing the risk of abnormalities are as follows:
Maternal Age. Aging women have a higher risk of giving birth to babies with abnormal chromosomes.
Environment. No conclusive study shows the specific factors that provoke the said abnormality. There is still a possibility that they play—a role in the occurrence of erroneous processes.
What is the smallest chromosome?
Chromosome 21 is the smallest and has an approximate number of 48 million bonded bases. They represent 1.5 to 2 percent of the DNA’s entirety.
In 2000, Genome Project discovered Chromosome 21 as the second human sequenced pair. It contains 200 to 300 genes that aid in the production of proteins and have various roles in the body.
Chromosomal conditions associated with changes in the structure may yield the following:
Down Syndrome is often caused by trisomy 21, having three copies instead of 2. The extra copy disrupts the normal development of the individual. It also increases the risk of developing seizures, endocrine problems, or Alzheimer’s disease.
Core binding factor acute myeloid leukemia is due to translocation written as t(8:21). The denotation of genetic changes is somatic mutation meaning it is not inherited. Tolerating the production of abnormal leukocytes develops cancerous leukemia cells.
Other Chromosomal Conditions. Any changes in the smallest chromosomes may affect one’s health and development. It may cause intellectual disability, delayed development, and distinctive facial features. Some cases show symptoms incongruent with Down Syndrome.
What is the largest chromosome?
Meanwhile, the largest one is Chromosome 1, with an estimation of 249 million DNA bonded bases. They represent 8 percent of the entire partition of the cell’s DNA. It contains 2,000 to 2,100 genes that aid in the production of proteins and have various roles in the body.
Sudden changes in its structure may lead to chromosomal conditions:
1p36 deletion syndrome occurs when deleted genetic material happens in the ‘p’ arm. The size of the deletion varies to the affected individuals. Signs and symptoms include intellectual disability or distinctive facial features.
1q21.1 microdeletion arises from a deletion part of each cell’s ‘q’ arm. Once affected, individuals are missing with 1.35 million DNA building blocks. Individuals may have delayed development, intellectual disability, and neurological problems.
1q21.1 microduplication is a copied segment on the 2 copies of chromosome 1 in each cell. It involves approximately 1.35 million missing two bond chemical bases. Apart from developmental delays, they may encounter psychiatric disorders such as schizophrenia.
Neuroblastoma is a cancerous tumor and an associated disease due to 1p36 deletion. At present, researchers are still studying how it aids in neuroblastoma development.
Thrombocytopenia Absent Radius Syndrome caused by the deletion of 1.q21.1. It eliminates at least 200,000 DNA building blocks from the ‘q’ arm. TAR’s denotation is by the absence of radius in each forearm and platelet shortage.
Other cancers due to chromosomal changes are somatic. ‘p’ arm deletion implies a tumor in the brain and kidneys. Meanwhile, duplication in the ‘q’ arm suggests blood and bone marrow disease.
Are males XY or YY?
Male has an XY pair as they inherited the X chromosome from the mother and Y from the father.
Dissecting the difference, males have an XY pairing during XX for females. In other words, fathers can contribute X or Y while mothers always contribute an X.
In the aspect of its size, Y chromosomes are only one-third of the X size. Meanwhile, Y- carries 55 basic units of hereditary while X- contains 900.
The XY served as a sex-determination system in humans, reptiles, and plants. For a fact, the expression of Y-linked genes is only for males. The other term for the male determining gene of Y is the SRY gene.
Why do we have 2 of every chromosome?
Chromosomes are in pairs because each parent contributes one of its own. Otherwise stated, one chromosomal pair is being inherited from their biological parents. One set for the mother and the other for the father.
If there are 23 chromosomal pairs, there will be 23 from the mother and another 23 for the father. The chromosome sets may inherit the copy of each gene to their children. Hence, 22 of the said bonded chemical bases are autosomes, and the remaining is a sex chromosome.
In maintaining the exact number of chromosomes, they must undergo mitosis. The process involves the division of DNA, yielding 2 identical cells. It ensures the old and new cells have similar genetic makeup and contain the same parent cell number.
Mitosis occurs in non-reproductive somatic cells. In comparison with meiosis, it occurs in sexual reproduction.
For reproduction to come to happen, it creates 4 new daughter cells. It creates 4 new daughter cells with slight distinctive genetic make ensuring diversity. They ended as haploid, meaning they contained half the number of chromosomes.
In contrast, mitosis only splits once since they only create 2 daughter cells. No pairing of homologous chromosomes, unlike meiosis. Thus, the cells produced are identical and end as a diploid with the same number of chromosomes.
How many genes does a chromosome have?
The Human Genome Project was an international collaborative effort in studying human genes.
Based on their findings, the human genome comprises about 3 billion bonded bases. They situate themselves in the chromosomes bond chemical bases within the nucleus.
Furthermore, it specifies the estimation of genes present for about 30,000. The following are the estimation of chromosome pairs according to their number/letter:
- About 3,000 basic units of inheritance with an estimation of 240 million base pairs. The determination of two bonded chemical bases is approx 90%.
- An estimation of 1900 genes with 200 million base pairs. The determination of two bonded chemical bases is appro 95%.
- More or less 1900 basic units of inheritance with 200 million base pairs. The determination of two bonded chemical bases is approx 95%.
- Around 1600 genes with 190 million base pairs. The determination of two bonded chemical bases is approx 95%.
- About 1700 basic units of inheritance with 180 million base pairs. The determination of two bonded chemical bases is approx 95%.
- More or Less 1900 genes with 170 million base pairs. Determination of pairs is approx 95%.
- An estimation of 1800 basic units of inheritance with 150 million base pairs. The determination of two bonded chemical bases is approx 95%.
- About 1400 genes with 140 million base pairs. The determination of two bonded chemical bases is approx 95%.
- Around 1400 basic units of inheritance with 130 million base pairs. The determination of two bonded chemical bases is approx 85%.
- More or Less 1400 genes with 130 million base pairs. The determination of two bonded chemical bases is approx 95%.
- About 2000 basic units of inheritance with 130 million base pairs. The determination of two bonded chemical bases is approx 95%.
- Around 1600 genes with 130 million base pairs. The determination of two bonded chemical bases is approx 95%.
- More or Less 800 basic units of inheritance with 110 million base pairs. The determination of two bonded chemical bases is approx 80%.
- About 1200 basic units of inheritance with 100 million base pairs. The determination of two bonded chemical bases is approx 80%.
- Around 1200 basic units of inheritance with 100 million base pairs. The determination of two bonded chemical bases is approx 80%.
- About 1300 genes with 90 million pairs. The determination of two bonded chemical bases is approx 85%.
- More or Less 1600 basic units of inheritance with 80 million base pairs. The determination of two bonded chemical bases is approx 95%.
- About 600 genes with 70 million base pairs. The determination of two bonded chemical bases is approx 95%.
- More or less 1700 basic units of inheritance with 60 million base pairs. The determination of two bonded chemical bases is approx 85%.
- Around 900 genes with 60 million base pairs. The determination of two bonded chemical bases is approx 90%.
- More or less 400 basic units of inheritance with 40 million base pairs. The determination of two bonded chemical bases is approx 70%.
- About 800 genes with 40 million base pairs. The determination of two bonded chemical bases is approx 70%.
X. Around 1400 basic units of inheritance with 150 million base pairs. The determination of two bonded chemical bases is approx 95%.
Y. More or Less 200 genes with 50 million base pairs. The determination of two bonded chemical bases is approx 50%.
The project does not only quantify genes but to get a complete mapping and understanding. HGP optimized the data analysis to 99.99% accuracy and sequenced the entire genome. Genome refers to genes in general or the organism’s complete set of DNA.
HGP revolutionizes the diagnosis and treatment of many illnesses. It benefited both medical science and impacts on drug discovery.
Collins, F.S. & McKusick, V.A. (2001). Implications of the Human Genome Project for Medical Science. National Library of Medicine. https://pubmed.ncbi.nlm.nih.gov/11176855/
Germanna Community College (n.d.). Mitosis vs. meiosis.content/uploads/tutoring/handouts/Mitosis-vs-Meiosis.pdf
Medline Plus (2022). Chromosome 1. National Library of Medicine. https://medlineplus.gov/genetics/chromosome/1/#resources
Medline Plus (2022). Chromosome 21. National Library of Medicine. https://medlineplus.gov/genetics/chromosome/21/#conditions
Medline Plus (2022). How many chromosomes do people have? National Library of Medicine. https://medlineplus.gov/genetics/understanding/basics/howmanychromosomes/\
Medline Plus (2022). What is a. chromosome? National Library of Medicine. https://medlineplus.gov/genetics/understanding/basics/chromosome/
National Human Genome Research Institute (2022). Chromosome abnormalities fact sheet. https://www.genome.gov/about-genomics/fact-sheets/Chromosome-Abnormalities-Fact- Sheet
National Center for Biotechnology Information (1998). Chromosome map.
National Center for Biotechnology Information (2009). Appendix F chromosomal abnormalities.
National Human Genome Research Institute (2022). Human genome project FAQ.
National Human Genome Research Institute (2022). Y chromosome infographic.
Szalay, J. & Dobrijevic, D. (2022). Chromosomes: Facts about our genetic storerooms. Live Science.
Your Genome (2022). What is chromosome?
Written by Ysandra Prille A. Tabilon
Ribonucleic acid is one of the major biological macromolecules essential to life. It is a nucleic acid that is present in the majority of living organisms and viruses. It is famous for its role in synthesizing proteins in your body. It also replaces deoxyribonucleic acid as a carrier of genetic code in many viruses.
A central dogma of molecular biology asserts that genetic code flows from DNA to RNA to proteins. It is Deoxyribonucleic acid that makes RNA, and RNA makes the proteins needed for your body. In this role, it is Ribonucleic acid that plays the “DNA photocopy” of the cell.
Basic Structure and Composition of RNA
Nucleotides are the nucleic acid’s basic building blocks. Ribonucleic acid, together with DNA, is a polymer made of long chains of nucleotides. A nucleotide of an RNA consists of a sugar molecule called ribose. This sugar attaches itself to a phosphate group and a nitrogen-containing base.
RNA’s nitrogen bases include adenine, guanine, uracil, and cytosine. They consist of a long, single-stranded chain. But, there are some special RNA viruses that are double-stranded. The molecule can have a variety of lengths and structures.
Types of Ribonucleic Acid
There are various types of Ribonucleic Acid. But, the most well-known and studied in the human body are the following:
Messenger RNA (mRNA). It is a molecule produced as a result of transcription. It carries the genetic code from the nucleus to the ribosomes for protein synthesis. It then transmits instructions on the type of proteins your body cells need.
Transfer RNA (tRNA). It is a molecule that transfers amino acids to the ribosomes for protein synthesis. It also assists in the translation of an mRNA sequence to proteins. It does this by forming base pairs with its complementary sequence on the mRNA.
Ribosomal RNA (rRNA). It is the ribosome’s most essential and prevalent structural component for all organisms. This molecule is necessary for the synthesis and translation of mRNA into proteins.
Functions of Ribonucleic Acid
One of the main functions of RNA is to help in the translation of DNA into protein. When your cells need a certain protein, they activate the gene that codes for that protein. It then generates several copies of that genetic information in the form of mRNA.
The mRNA copies are then used to translate the genetic information to protein. It accomplishes this action via the ribosomes, the cell’s protein production machinery. Thus, it increases the quantity of a protein produced by a single gene. Also, it acts as a control point for determining the time and amount of protein produced.
Ribonucleic acid depending on its type, has a variety of functions within the cell. They act as structural molecules within the organelles of cells. They also have a role in the catalysis of biological reactions. Other functions of Ribonucleic Acid are the following:
- Carrier of genetic information all living cells
- In protein synthesis, it serves as an adapter molecule
- Intermediary between Deoxyribonucleic acid and ribosomes
- Assists the ribosomes in choosing the appropriate amino acid needed for protein synthesis.
- Act as enzymes (ribozymes) to speed chemical reactions
How is RNA created? What is RNA and what is its function?
Transcription is a process that converts DNA into Ribonucleic acid. It entails copying the gene sequence to create an RNA molecule. The primary enzymes involved in transcription are RNA polymerases. This enzyme synthesizes a complementary strand of RNA from a single-stranded gene template.
3 Stages of Transcription
Initiation. An RNA polymerase enzyme binds to a segment of DNA called the promoter. After binding, the double helix of DNA unwinds into a template strand and a non-coding strand. The single-stranded template is the one needed for transcription.
Elongation. The RNA polymerase reads the template strand in the 3′ to 5′ direction during this stage. Each nucleotide can synthesize a 5′-3′ RNA strand with complementary nucleotides. The newly synthesized RNA strand is almost identical to the non-coding strand. But, it contains the base uracil (U) instead of thymine (T).
Termination. RNA synthesis will continue until it comes across a signal instructing it to stop. Terminators are the sequences that signal that the transcript is complete. Once transcribed, they cause the RNA polymerase to release the transcript.
What came first protein or RNA?
The conflict between RNA and protein over who came first is analogous to the chicken or egg problem. Many people believe it is the RNA, while others believe it is the protein.
But if you consider the central dogma, it states that DNA generates RNA, which in turn makes proteins. So that implies that Ribonucleic Acid came first than proteins.
The dogma states that DNA contains the information needed to make your proteins. Ribonucleic acid serves as a messenger, conveying this information to the ribosomes. Translation refers to the process of converting ribonucleic acid to proteins.
According to the RNA world hypothesis, life on Earth evolved from a single RNA molecule. In this hypothesis, it says that this molecule evolved before DNA and proteins. It also says that it is capable of self-replication without the help of other molecules.
The general order has to be Ribonucleic acid first, then proteins, then DNA. Ribonucleic acid is like the ancestral molecule of life. Like deoxyribonucleic acid, RNA is capable of storing and replicating genetic information. Also, it can catalyze chemical reactions necessary for life, like protein.
Additionally, the well-known Urey-Miller experiment may reveal that proteins came first. Amino acids, the building blocks of protein, appeared to have formed during the early Earth’s formation.
The RNA-First scenario is quite popular among scientists studying the origins of life. But, there is insufficient evidence to explain what hypothesis is actually true.
What is the difference between RNA and DNA?
Deoxyribonucleic acid and Ribonucleic acid are nucleic acids. They both contain monomers called nucleotides. But, they, too, perform different functions and have distinct characteristics between them.
DNA has a role in the storage and transmission of genetic code needed for the formation of your other cells. While Ribonucleic acid transmits these codes to the ribosomes to synthesize proteins.
The location of DNA is in the nucleus, while some are present in the mitochondria. It is self-replicating and cannot leave its location. Meanwhile, RNA forms in the nucleolus and moves to the cytosol and ribosomes. Also, it gets synthesized from deoxyribonucleic acids.
DNA contains deoxyribose sugar, which is why it’s referred to as deoxyribonucleic acid. It also has two strands that twist to form a double helix. Meanwhile, RNA has ribose sugar hence the name ribonucleic acid. It only has a single strand of nucleotide, forming a helix.
They also differ in their sizes and helix geometry. DNA is way larger than RNA since it has millions of long-chain nucleotides that shape into a B-form helix. This increases the susceptibility of it to UV damage.
By contrast, Ribonucleic acid is much smaller. It has hundreds of shorter nucleotide chains that form into an A-helix. It also has a higher UV resistance than deoxyribonucleic acid.
Moreover, Ribonucleic Acid’s chemical structure is quite like that in DNA. Yet, both of them have some distinctions. DNA contains a sugar group with a 2′ hydrogen, while RNA contains a 2′ hydroxyl group.
DNA is stable under alkaline conditions due to its C-H bonds. While the O-H bond in RNA’s ribose makes it more reactive. That is why it is not stable under alkaline conditions. Also, due to the large grooves on its molecule, it is prone to enzyme attack compared to DNA’s smaller grooves.
Another key difference is their pyrimidine base and base pairing. They both contain four nitrogenous bases. But, deoxyribonucleic acid contains thymine that pairs with adenine. While Ribonucleic acid has the nucleobase uracil to pair with adenine.
Can RNA turn into DNA?
Ribonucleic acid can convert into deoxyribonucleic acid through a process called reverse transcription. This process is in contrast to the central dogma’s DNA-to-RNA flow. It is the reverse process of normal cellular respiration.
Reverse transcriptase is the enzyme that generates complementary DNA from an RNA template. This process is more prevalent and essential for retroviruses to be infectious. Reverse transcriptase was first discovered in retroviruses. But, new studies reveal that it is present in viruses, bacteria, animals, and plants.
An example of a retrovirus that uses reverse transcription is HIV. It can insert its genetic code into the genomes of infected cells. It replicates the HIV RNA and converts it to double-stranded DNA. It then incorporates itself into the cell’s DNA and orders the cell to replicate the virus.
Moreover, Thomas Jefferson University scientists were able to make history. They were the first to prove that mammalian cells can revert RNA segments to DNA. These findings could challenge the central dogma and have wide implications. This could imply that RNA messages can serve as templates for gene repair or rewriting.
Is RNA self replicating?
The replication of the genome is necessary for life to continue. One of the characteristics of living things is their potential for reproduction. You might be aware that Deoxyribonucleic acid is self-replicating, but what about RNAs?
According to the RNA world hypothesis, RNAs may be the first discovered molecule. This molecule has diverse functions like those of Deoxyribonucleic Acid. Ribozymes are small RNA structures that carry out chemical reactions necessary for life. Besides that, this enzyme might be able to replicate Ribonucleic acids.
Scientists have been attempting to recreate a self-replicating RNA to test this theory. So far, they only developed ribozymes capable of replicating only the straight strands. But, when folded, it is incapable of self-replication.
Yet, eventually, self-replication became possible. James Attwater has developed a ribozyme capable of replicating folded RNA strands. James isolated these ribozymes capable of replicating small segments of folded RNA. He then engineered the best version to replicate and create new full synthetic copies. This is the molecule’s first instance of self-replication.
For years, researchers have speculated that there might be a simpler way to copy RNA from DNA itself. Yet, now they have finally synthesized RNA enzymes capable of self-replication. Even in the absence of proteins or other components, these molecules can replicate.
Ribozymes are the ones that are self-replicating. Although, not all RNAs are self-replicating.
Can RNA exist without DNA? What is RNA and what is its function?
Deoxyribonucleic acid is the genome of all self-replicating cellular organisms studied thus far. Also, they perform all biological functions under the central dogma. As a result of this fact, almost all biologists must believe that no organism exists without DNA.
But, some scientists still believe that an organism devoid of DNA could exist on Earth. This type of organism may exist in the world of microorganisms. It is an area of enormous biological diversity. The majority of microorganisms still remain unidentified. If you think about it, anything is possible.
Scientists have devised experimental methods to identify organisms that lack DNA. They employed techniques that inhibit DNA replication or expression. They conducted it on 100 microbial samples collected from a variety of water sources. They were able to discover colonies and cells that appeared to be DNA-free. But, it turns out they were DNA-positive.
So far, no microorganism without Deoxyribonucleic acid has been identified. The findings reveal that there may be no such organisms or that they exist on Earth but are very difficult to find. Nonetheless, some scientists believe that these types of organisms exist in our environment.
So, to answer your question on the existence of RNA without DNA, there have been no findings of such organisms yet. The discovery of RNA organisms could alter our understanding of evolution and biology. It is likely to be an organism that has developed alone and is distinct from DNA organisms.
Brennan, J. (2017, April 25) Did Protein, DNA or RNA Come First? Sciencing. https://sciencing.com/did-protein-dna-rna-come-first-2237.html
BYJUS (n.d.) Structure of RNA. https://byjus.com/biology/structure-of-rna/
Helminstine, A.M. (2020, February 2) The Differences Between DNA and RNA. ThoughtCo. https://www.thoughtco.com/dna-versus-rna-608191
Hiyoshi, A. et al. (2011, November 17) Does a DNA-less cellular organism exist on Earth?
Wiley Online Library. https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2443.2011.01558.x
India Today (2018, November 16) Major differences between DNA and RNA. India Today. https://www.indiatoday.in/education-today/gk-current-affairs/story/differences-between-dna-and-rna-1389884-2018-11-16
Khan Academy (n.d.) Overview of transcription.
MC Laboratory of Molecular Biology (2018, May 16) How the earliest life on Earth may have replicated itself.
https://www2.mrc-lmb.cam.ac.uk/how-the-earliest-life-on-earth-may-have-replicated-itself/ RNA Society (n.d.) What is RNA. https://www.rnasociety.org/what-is-rna
ThermoFisher Scientific (n.d.) Reverse Transcription—A Brief Introduction. ThermoFisher. https://www.thermofisher.com/ph/en/home/life-science/cloning/cloning-learning-center/invitroge n-school-of-molecular-biology/rt-education/reverse-transcription-basics.html
Thomas Jefferson University (2021, June 12) New Discovery Shows Human Cells Can Write RNA Sequences Into DNA – Challenges Central Principle in Biology. SciTechDaily. https://scitechdaily.com/new-discovery-shows-human-cells-can-write-rna-sequences-into-dna-ch allenges-central-principle-in-biology/amp/
Scripps Research Institute (2009, January 10) How Did Life Begin? RNA That Replicates Itself Indefinitely Developed For First Time. ScienceDaily. https://www.sciencedaily.com/releases/2009/01/090109173205.htm
Wang, D. & Farhana, A. (2021, May 9) Biochemistry, RNA Structure. NCBI. https://www.ncbi.nlm.nih.gov/books/NBK558999/#:~:text=The%20primary%20function%20of%20RNA,RNA%20involved%20in%20protein%20synthesis
Written by Elijah Dave M. Cordova
Histology is a fascinating field of study. It helps you understand how normal tissues appear. It teaches you how they function. It helps confirm the presence of several diseases. Histology allows you to trace the causes of diseases. It can also teach you how to treat them.
The term “histology” comes from two Greek words. “Histos” means tissue, and “-logos” is a field of study. Hence, it deals with the study of the tissues in the body. It studies how they constitute the different body organs. It focuses on how cells’ order and structure optimize the organs’ functions.
Recall the different levels of organization in organisms.
- Cells are the most basic structures that constitute life.
- Tissues comprise cells similar in function and form. They work together to perform the same functions.
- Organs are tissues that work together to do specific activities.
- Organ systems are many organs that work together to perform needed roles. These functions benefit the organism in normal conditions.
The interconnectedness of histology to other study fields is obvious here. Among these fields are the following:
Histology grants a microlevel perspective on these subjects and more. Many students who prefer more generalized and applicable studies might find it boring. Yet, without it, these other studies would fail to make sense.
Through this article, you will get to learn more about histology. You will discover its main goals and concepts. You will appreciate its relationship with other fields in medicine. Moreover, you will realize the privilege that is the chance to learn this subject.
What are the basic concepts of histology?
Now that you know its importance, you might wonder how to start studying histology. It begins by learning what makes up tissues. Next, you will learn how to prepare tissue sections for examination. What follows is a discussion on the different microscopes you can use.
Cells and the extracellular matrix (ECM) make up tissues. Several macromolecules form the ECM. Among them are collagen fibrils which are the building blocks of tendons.
The ECM aids the cell and contains the fluid that serves three purposes.
- It transports nutrients to the cells;
- It provides mechanical support for the cells; and
- It transports cell wastes and other secretory products.
Cells produce ECM components. These components, in turn, influence cells. This relationship causes intense interactions between these two components. These interactions create different types of tissues, each having unique features.
The minute size of the cells and ECM elicits the need for microscopes. Hence, the most common procedure in histology is the preparation of tissue sections. These are thin and translucent organ slices. The basic steps to prepare tissues for examination under light microscopy are here:
- Fixation is placing tissue sections in fixatives. These are solutions with cross-link proteins that inactivate degradative enzymes. Hence, they preserve the tissue structures.
A buffered isotonic solution of 37% formaldehyde is a usual light microscopy fixative. Meanwhile, glutaraldehyde is a prevalent electron microscope fixative.
2. Dehydration is placing the sections through increasing concentrations of alcohol solutions. The final solution is 100% alcohol.
3. Clearing is removing the alcohol in the samples through organic solvents. These solvents are miscible in alcohol and embedding mediums. Common embedding mediums are paraffin and xylene.
4. Infiltration is placing the sample in melted paraffin. You perform this at 52°- 60°C.
5. Embedding is placing the paraffin-infiltrated tissue in a mold. It allows your samples to harden. It is often done at room temperature.
6. Trimming is slicing or sectioning the hardened sample. It does this through an instrument called a microtome. This microtome creates 3-10 μm thick tissue sections for light microscopy.
7. Staining (dyeing) makes tissues distinguishable from one another. Its necessity is due to most cells and ECM components being colorless.
Cell components with an anionic (negative) charge react well with basic dyes or stains. These components are basophilic. Examples include DNA and RNA.
Cationic (positive) substances react with acidic dyes. These substances are acidophilic. Examples are collagen and several cytoplasmic proteins.
Hematoxylin and eosin (H&E) are the most common staining dyes. The former is a basic dye, and the latter is acidic.
8. Mounting a glass coverslip on the slide is the last step. The coverslip must have a clear adhesive.
Slide preparation (steps 1 through 8) takes around 12 hours to 2½ days. Its duration depends on tissue size, staining method, and embedding medium.
There are two types of microscopes you can use in histology. They are as follows:
- Light microscopy uses the interaction of light with tissue components.
- Bright-field microscopy identifies tissues through colors caused by staining. Students and pathologists use this the most.
- Fluorescence microscopy uses UV light to visualize fluorescent molecules alone. It allows fluorescent probe localization that is more specific than routine stains.
- Phase-contrast microscopy produces stain-less images. Hence, it allows you to observe living cells. It does this through refractive index differences among tissue components.
- Confocal microscopy scans samples at successive focal planes to generate images. It often uses a laser. Confocal microscopy produces a 3D reconstruction with the image.
- Electron microscopy uses the interaction of electron beams with tissue components.
- Transmission electron microscopy (TEM) permits resolutions around 3 nm. It allows up to 400,000x magnification. You can add compounds with heavy metal ions to the fixatives here to improve resolution. You can also perform cryofracture and freeze etching. Here, you freeze the specimen in liquid nitrogen before cutting it.
- Scanning electron microscopy (SEM) produces black-and-white images. It presents a 3D view of the specimen.
Other ways of studying histology samples are the following:
- Autoradiography uses radioactive precursors to localized synthesized cell components.
- Cell and tissue culture is growing cells in vitro. You will often use the phase-contrast microscope here.
- Enzyme histochemistry (cytochemistry) uses specific enzyme activities in samples. It yields visible products in specific enzyme locations. You will often use a cryostat here.
- Immunohistochemistry visualizes specific molecules in samples. It uses antigen-antibody reactions with visible markers.
- Hybridization techniques localize DNA sequences on chromosomes. They also detect specific RNA targets in cells. In situ hybridization (ISH) is a common hybridization technique.
What are the four types of tissue? Describe each.
You now know the basic concepts in histology. You may next wonder what kinds of tissues there are in our bodies. The epithelium and connective tissue are among them. The muscle and nervous tissues complete this list.
The epithelial cells (epithelium) have the following functions:
- Absorption. It includes the gut (intestinal lining) and the stomach.
- Filtration. An example is a kidney.
- Protection. It involves the skin that protects us from the outside world.
- Secretion. It includes the different glands in our bodies.
They have the following characteristics:
- A free (apical) surface open to outside the body. It can also be in internal organ cavities in the body.
- A fixed (basal) area connected to underlying connective tissue
- Can have several nerves in them (innervated)
- Excellent regeneration as seen in sunburn
- Forms a protective barrier through close attachment to each other
- No blood vessels
They, too, have the following classifications:
- By cell arrangement.
a. Simple. They are single-cell layers often used for absorption and filtration.
b. Stratified. They have several layers often used for protection.
2. By shape.
a. Columnar. These are column-shaped and tall.
b. Cuboidal. These take the form of a cube.
c. Squamous. These are scale-like and flat.
Meanwhile, connective tissues have the following functions, elements, and classifications.
- Cushioning and internal support for organs.
2. Protects and attaches body parts. Examples include tendons and ligaments.
3. Stores nutrients.
4. Strengthens the skin.
2. Fibers provide elasticity, support, and strength.
3. Ground substance is a gel around the cells and fibers.
- Loose connective.
- Adipose. These have blood vessels and cells. They also store nutrients.
- Areolar connective. These are a loose arrangement of cells and fibers. They provide cushions to organs
- Reticular connective. These are delicate fiber-cell networks. They provide internal support to organs.
- Dense connective
Dense regular connective. These include tendons and ligaments. They often have fibers and provide strength.
Dense irregular connective. These include the skin and organ capsules. They often have fibers going in all directions.
Next are the jobs and elements of nervous tissues.
- Conducts impulses to and from organs through neurons.
Last are the jobs and types of muscle tissues.
- In charge of body movement.
2. Transports waste, food, and blood through the body organs.
3. Responsible for mechanical digestion.
- Cardiac muscle. It is the muscles that make up the heart. These muscles are involuntary and striated. They have intercalated discs that cause synchronous heart contractions.
2. Skeletal muscle. It includes all the body muscles. They are voluntary and striated. They connect to bones to aid movement. They, too, come in bundles.
3. Smooth muscle. It includes all blood vessels and organ walls. These muscles are involuntary and spindle-shaped. They push materials through organs.
What is the difference between histology and biopsy?
You now know the basic types of tissues. Let us now discuss the terms associated with histology. The first is a biopsy. A biopsy is a procedure of taking small tissue samples. It also refers to the tissue sample itself. Meanwhile, histology is a study field that uses biopsies in diagnosing diseases.
Biopsies often diagnose or rule out the following diseases:
- Peptic ulcers.
- Kidney diseases.
Also, among the types of biopsies are as follows:
- Endoscopic biopsy. You can use it during an endoscopy which visualizes the upper GI tract. It uses an endoscope to remove tissues.
2. Excisional biopsy. You can use this in surgery to remove larger tissue sections.
3. Needle biopsy. It uses a hollow needle to get organ or skin tissue sections.
What is the difference between histology and pathology?
Next to a biopsy is pathology. Pathology is a branch in the field of medicine. It studies the nature and causes of diseases. It, too, investigates their development and effects. Histology has roots in biology. It involves the small tissue structures and their composition.
Histology can benefit the study of pathology. It helps explain how and why certain diseases afflict humans. Pathology can also benefit histology. Its study provides applications of what histologists identify under their microscopes.
What is the difference between biopsy and histopathology?
Last is the term histopathology. It combines histology and pathology. Histology studies tissues, and pathology studies diseases. Hence, histopathology studies tissues related to disease. A biopsy is the removal of tissue samples for clinical examination. It also refers to the actual tissue samples.
Biopsies are crucial to the field of histopathology. They help in diagnosing diseases from tissue samples.
Why should I study histology?
Histology is interesting. It allows you to see and appreciate the world in a different way. It gives you a thorough understanding of the microstructures that make you, you. Histology also sits at the crossroads of anatomy, pathology, and physiology.
Aside from this, there are other applications for histology:
- Autopsies. Studying tissues from a deceased human or animal can help determine the cause of death.
2. Forensic investigations. Tissue sample studies can clarify several forensic issues. Hence, they can help solve crimes.
3. Veterinary diagnosis. Animal samples can suggest ways to treat and manage their conditions.
Ali, R. (n.d.). Introduction to Basic Histology. UO Babylon. Retrieved February 20, 2022 from uobabylon
Brown, R. (2021). What is a biopsy? Rcpath.org. pathology/news/fact-sheets/what-is-a-biopsy.html#:~:text=Histopathologists%20examine%20biopsies%20(tissue%20or,more% 20detail%20under%20the%20microscope.
Exploring Nature. (n.d.). from exploring nature. The 4 Basic Tissue Types in the Human Body
Histology vs. Pathology – What’s the difference? | Ask Difference. (2018). Askdifference.com.
Introduction to Histology – Applications & Importance – Anatomy Notes. (2020, January 14). Anatomy Notes. https://anatomynotes.org/histology/introduction-to-histology- applications-importance/
Mescher, A. (2018). Junqueira’s basic histology : text and atlas (15th ed.). Mcgraw Hill Education.
Thompson, V. (2014). Why Is the Study of Histology Important in Your Overall Understanding of Anatomy & Physiology? Education – Seattle PI. https://education.seattlepi.com/study- histology-important-overall-understanding-anatomy-physiology-5337.html
Written by Kheizaya Methuzela G. Aguirre
Histology includes studying tissues and cells under a microscope. Histologists perform this to diagnose and research disorders of the tissues. They make tissue diagnostics and assist doctors in patient care management.
People study histology to:
- Examine the contents of the tissue.
- In agriculture, they seek what chemicals are present in the soil.
- Perform autopsies in this field. It is to comprehend better some inexplicable deaths during autopsy and forensic investigations. Microscopic tissue analysis may reveal a cause of death in some circumstances.
Why is it called histology?
Histology is a study that deals with cell and tissue structure at the microscopic level.
Its name comes from the Greek term “histos,” which means tissue or columns. The other is “logia,” which refers to “study.”
Histology first appeared in a book written by Karl Meyer in 1819. It was where he combined the two Greek words. And it was then traced back to the 17th century by Marcello Malpighi.
He experimented with insects, botany, and embryology as a scientist. He was the first to use the silkworm as a model to study insect respiration.
He also further investigated the development of chick embryos than anybody else. His experiments are what made him a pioneer in the science of embryology.
But it was his delineation of pulmonary capillaries and alveoli that made him famous. Using only a single magnifying lens, Malpighi saw pulmonary capillaries in the frog.
He termed these capillaries as “nature’s microscope.” It allowed him to see things that are not present in big animals.
Although he uses these single lenses in most of his findings, he also utilized a new microscope. This new type is the compound microscope, which arose at the end of the 16th century. It allowed him to see chick embryo development.
Here are some human body structures named after Malpighi:
- Malpighian corpuscles
- Malpighian layer in the skin
- Malpighian tubules of the insect’s excretory system
How is tissue classified?
Tissues refer to a collection of cells with similar structures and play a specific role. Histology focuses on tissues’ appearance, structure, and function under a microscope.
Below are the classifications of tissues based on their structural and functional similarity:
- Neurological systems
The fundamental tissue collaborates to assist the human body’s general health and maintenance. As a result, any change in tissue structure might result in harm or illness.
Epithelial tissue is the body’s outer cover, lines interior cavities, and forms glands. As its name indicates, connective tissue ties the body’s cells and organs together.
When the body stimulates muscle tissue, it contracts, allowing mobility. Nervous tissue is also reactive. It enables electrochemical signals to generate and propagate into nerve impulses. When this happens, it communicates to the different parts of the body.
What are examples of tissues?
In histology, we all know that there are four types of tissues:
- Each of these tissues has examples of their structure and biological function. Under the epithelial tissue, you have the following:
- Simple Squamous
- Simple Cuboidal
- Simple Columnar
- Stratified Squamous
- Stratified Cuboidal
- Stratified Columnar
- Pseudostratified Columnar
The simple squamous allows items to flow through diffusion and filtration. It also emits lubricating substances. It resides on the lining of the heart, blood vessels, and lymphatic vessels, as well as the air sacs of the lungs.
Simple cuboidal epithelium ingests and secretes. It is in ducts and secretory parts of tiny glands and kidney tubules.
Simple columnar consumes and releases mucus and enzymes. They are on ciliated tissues like lungs, uterine tubes, and uterus. The digestive tract bladder also contains smooth (nonciliated tissues).
Transitional epithelium allows for the expansion and stretching of the urinary organs. The bladder, urethra, and ureters are all lined with it.
Stratified squamous epithelial tissue is the skin protector against abrasion. The esophagus, mouth, and vaginal canal are all lined with this substance.
Stratified cuboidal is present in sweat, salivary, and mammary glands. All these mentioned glands have a protective epithelial layer.
The stratified columnar epithelium is an uncommon kind of epithelial tissue. It has quite a few layers of column-shaped cells. The conjunctiva, throat, anus, and male urethra are some places where it situates. It also occupies the embryo.
Pseudostratified columnar epithelia are tissues that constitute a single layer of cells. But, they appear to look like they are of many layers when seen in cross-section. These epithelial cells’ nuclei are at various levels, giving the appearance of stratification.
- Connective tissue is another type of tissue that functions as a linking role in the body. It works to support and bind other tissues.
Examples of specialized connective tissues are:
Adipose tissue is a fat-storing connective tissue. It protects organs and insulates the body from heat loss by lining organs and cavities in the body. Hormones produced by this affect blood coagulation, insulin sensitivity, and fat accumulation.
Cartilage is a tissue composed of packed collagenous fibers encased in chondrin. This chondrin is a rubbery and gelatinous material. Sharks and human embryos have cartilage in their bones. It offers flexible support for tissues such as the nose, trachea, and ears in mature humans.
Collagen and calcium phosphate, a mineral crystal, are all seen in bone tissue. It is a mineralized connective tissue made up of calcium phosphate for hardness.
Scientists classify blood as a form of connective tissue. It originates from the mesoderm, the central germ layer of growing embryos. The blood also functions to connect different organ systems. It carries signal molecules between cells to supply them with nutrients.
Another form of fluid connective tissue is lymph. Blood plasma exits blood vessels at capillary beds, resulting in this transparent fluid. It contains immune system cells that defend the body from infections.
- And for the muscle tissues, below are the examples that you must know about it:
- Smooth muscle
- Skeletal muscle
- Cardiac muscle
Smooth muscle is present in the intestines, blood vessels, urinary and reproductive systems. It contracts, causing peristaltic movement and blood vessel obstruction in the alimentary canal.
From the word “skeleton,” skeletal muscle links to the bones of our arms and legs. Voluntary motions involve the skeleton. To move bones, they contract and relax.
Cardiac muscle is a kind of muscle found in the heart. It settles in the heart’s walls where its cardiac muscle tissues are. They contract to pump blood to every region of the body.
- Nerve cells and their associated neuroglia cells make up nervous tissue. These cells receive and send nerve impulses or action potentials from one nerve cell to the next.
Dendrites and axons are two types of cellular projections found in nerve cells. The electrochemical signals are all received by the dendrites (from another nerve cell). The action potential will then forward to the next nerve cell via the axons.
The axon terminal is a bulb-like terminus to the axon. This axon terminal releases neurotransmitters that go to the next nerve cell of the body. It is to finally pass the nerve impulse from one nerve cell to another.
Neuroglia cells lie in the nervous tissue like the nerve cells. These cells assist in the protection and nourishment of nerve cells. They also aid in the maintenance of homeostasis and the formation of myelin.
The nervous system comprises nervous tissue. Nervous tissue comes in a variety of forms. Grey matter and white matter exist in the central nervous system. There are ganglion tissues and nerve tissues in the peripheral nervous system.
Where are the 4 tissues located?
Tissues are a bunch of cells with the same shapes and functions. Different organs contain different types of tissues. Listed below are the following four fundamental kinds of tissues found in humans.
- Nerve tissue
Within each of the primary tissues, there may be many sub-tissues. Each of them has its designated place in the human body where it operates. that you should know about.
Most inner cavities line epithelial tissue, covering the body’s exterior. The roles of epithelial tissue incorporate protection, secretion, absorption, and filtration.
An example of this is the skin protecting the body from dirt, germs, and other hazardous organisms. These tissue cells come in various forms – thin, flat, cubic, or elongated cells are all possible.
Connective tissues locate between other tissues everywhere in the body. They help bind structures to form frameworks and support organs. They store fat, carry chemicals, and guard against disease throughout the body. Additionally, they also help rectify tissue impairment.
Your muscle tissues are on your body’s muscles. These shorten or contract to produce motion of your body parts. The tissue is cellular and well-furnished with blood.
The nervous tissues in our body are all found in the brain, spinal cord, and nerves. They are in charge of supporting the nervous system in handling many functions.
How long does it take to become a histologist?
A histologist is someone who prepares tissue samples for examination by a pathologist. Its job is to cut tissue samples from organs or tissues and stain them with dyes. You use dyes to enhance the visualization of tissues for microscopic tissue examination.
There are times that you are also tasked to complete these activities immediately. Activities like taking a sample of tissue from a patient during surgery. You will also work on this when doing rapid laboratory analysis.
Becoming a histologist is quite long and requires patience. You must have either an associate or bachelor’s degree and a license to practice in the state where you work.
You may also need to earn certification from ASCP. Yet, this depends on your employer’s recommended job qualities.
This sector requires two years of laboratory experience. Thus, it necessitates meticulous attention to detail and knowledge of the equipment needed. Training in the handling of valuables is also part of the profession.
Students wishing to pursue this field must:
- Get a high school diploma and two years of histopathological clinical laboratory experience.
- Get an associate or bachelor’s degree in histotechnology.
- Finish at least a year of clinical lab experience in histotechnology.
- Get a license by passing the national examination.
Is histology a hard class?
Histology is beneficial to medical students in a variety of ways. It aids them in comprehending the typical organ system’s cell and tissue architecture. Furthermore, it links structure to function by tying tissue structure to operate.
Histology is somehow complex because it needs excellent memorization and understanding skills. But at the same time, it is a fascinating field of study. It’s amazing how intricate the tissues are while still being so similar.
You will still find the fascinating aspect of it. There is no single branch of biology that is very easy, with all honesty.
All fields need a thorough understanding because the scientific world is expansive. Yet, you won’t regret learning new things because uncommon ones are always interesting.
Anatomy and Physiology: Four Types of Tissues. (n.d). https://open.oregonstate.education/aandp/chapter/4-1-types-of- tissues/#:~:text=Tissues%20are%20organized%20into%20four,maintenance%20of%20th e%20human%20body.
Classification of Tissues. (n.d). https://www.vedantu.com/biology/classification-tissue Goldberg, Alexander. 2018, December 18. A Brief History of Histology.
Helmenstine, Anne Marie. 2019, March 24. What Histology Is and How It’s Used. thoughtco/histology
Stoppler, Melissa Conrad. 2021, March 29. Medical Definition of Histology. Medicinenet/histology
ZipRecruiter Marketplace Research Team. (n.d). What Is A Histologist and How to Become One. Ziprecruiter/histology