Written by Alexa Mae C. Niez

Edited and Reviewed by Reuben J C. Los Baños, Ph.D.

Ever wonder what you are made of? What components underlie your body? Well, you’re in luck, as we will tackle these topics, specifically Cells. As stated in the cell theory, these are present all over your body as this is an essential functional unit of all living organisms.

Cells are microscopic, surrounded by a membrane which encloses the cytoplasm within. As we go through this article, we will learn more about these tiny units that comprise your whole being.

Molecularly speaking, cells are made up of carbon-containing (organic) molecules, inorganic ions, and water. Structurally, it is divided into three parts–cellular membrane, nucleus, and cytoplasm. These can be unicellular or multicellular.

Molecular Components

Organic Molecules

Cells are made from the same significant classes of organic molecules: carbohydrates, lipids, nucleic acids, and proteins. These are unique components of the cells. Additionally, its structure and function can be understood by these materials.

Carbohydrates

These are the cells’ significant nutrients, including simple sugars and polysaccharides. This undergoes a process of breaking down that contributes to cellular respiration.

• Simple sugars – Also known as monosaccharides, they comprise single sugar molecules. These can join together to form oligosaccharides (few conjoint sugars) or polysaccharides through dehydration reactions.
• Common simple sugars are glucose, galactose, and fructose.
• Polysaccharides – Composed of many bonded sugar molecules. Also, the majority of the natural carbohydrates take this form. The connection between molecules can be separated through the hydrolysis reaction.
• Common polysaccharides are glycogen and starch.

Lipids

Contributes to energy storage, the formation of cellular membranes, and cell signaling. Its simplest form is the fatty acids, which comprise a carboxyl group at the end of lengthy hydrocarbon chains, usually up to 16-18 carbon atoms.

• Unsaturated Fatty Acids – Double bonds are present between carbon atoms.
• Saturated Fatty Acids – All carbon atoms bond with the maximum quantity of hydrogen atoms.

Since this has one nonpolar hydrocarbon bond, its hydrophobic characteristics enable it to be the main component for creating cellular membranes.

• Phospholipids – The main component of cell membranes is a combination of two fatty acids connected to a polar head. This has a hydrophobic tail containing two hydrocarbon chains and hydrophilic heads.
• Other common lipids are triglycerides and cholesterol.

Nucleic acids

They comprise nucleotides, building blocks that play a significant role in cell processes. DNA and RNA are nucleic acids, the cell’s main informational molecules.

• Deoxyribonucleic Acid (DNA) – Located in the nucleus of eukaryotic cells, it has a unique role as its genetic material.
• Ribonucleic Acid (RNA) – Produces proteins using amino acids and is responsible for numerous cellular activities. It has different types that have different purposes.
  • Messenger RNA (mRNA) – Helps in carrying information from the DNA to the ribosomes, hence its name.
  • Transfer RNA (tRNA) – This has a cloverleaf structure and consists of molecules that translate the mRNA into proteins.
  • Ribosomal RNA (rRNA) – Forms the ribosomes, essential for protein synthesis.

Proteins

It comprises amino acids, which are its building blocks. Derived from the Greek word proteios, which means “of the first rank,” it is the most crucial molecule in biological chemistry.

There are three types of amino acids: (Humans only use 20)

• Non-essential (5) – Can be obtained from food or in the body.Alanine, Asparagine, Aspartic acid, and Glutamic acid.

• Conditionally Essential (6) – Healthy bodies can be created under normal physiologic conditions. Critical for cases such as starvation or inborn errors of Metabolism.
  • Arginine, Cysteine, Glutamine, Glycine, Proline, and Tyrosine.

• Essential (9) – Cannot be generated from the body. These are from dietary proteins that make important molecules and specific hormones.
  • Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine, Tryptophan, and Valine.

Proteins execute tasks using information carried by genetic material. These are diverse and different proteins with several functions in each cell containing them.

Also, it serves as the structural component of cells and tissues, stores and transports small molecules, transmits information between cells, and defends against infections.

Its integral property is that it can act as an enzyme to catalyze almost all chemical reactions.

• There are four levels of structure: primary, secondary, tertiary, and quaternary.
• Primary – Amino acid sequence in polypeptide chains.
• Secondary – Regular assembly of amino acids in regions of polypeptides. Commonly, these can be α helix and β sheet.
• Tertiary – Folding of polypeptide chains due to interactions between amino acid side chains throughout various primary sequence regions.
• Quaternary – relationships between various polypeptide chains in proteins comprising many polypeptides. An example is the hemoglobin, the protein that brings color to our blood.

Inorganic Ions

The ions that are present in the cell and comprise 1% or less of the mass include sodium (Na⁺), potassium (K⁺), and magnesium (Mg²⁺). Calcium (Ca²⁺), phosphate (HPO42-), chloride (Cl^–), and bicarbonate (HCO3-). These ions participate in cell metabolism, which plays a critical role in its function.

• Sodium is an electrolyte cation that helps maintain homeostasis through osmoregulation, blood and body fluid volume, and pH regulation.
• Potassium ions help move nutrients inside the cell and excrete waste products.
• Magnesium ions function in enzymatic reactions, transferring, storing, and using energy.
• Calcium ions regulate enzymatic activities and cellular events such as muscle contraction, secretion, and cell division.
• Phosphate ions are responsible for enzymatic reactions such as glycolysis and ammoniagenesis and help form the phospholipid layer of cell membranes, DNA, RNA, and proteins.
• Chloride ions help regulate the extracellular compartment’s water, osmotic pressure, pH, and ion balance.
• Bicarbonate ions help with the pH homeostasis and transport of ions and organic substrates through cellular membranes.

Water (H2O)

Water is the most abundant component, accounting for 70% or more of its total mass. The interaction between the H2O in the cell is significant in its interaction with the other elements, specifically in biological chemistry.

Structural Components

Cell Membrane, also known as plasma membrane, is the cell covering that separates its interior from the surrounding environment. It consists of a semipermeable lipid bilayer, essential for transporting nutrients, ions, and substances in and out of the cell.

Cytoplasm is the thick-fluid content of the plasma membrane, which mainly comprises water, salts, and proteins. This houses the organelles and is the site of many cellular processes.

Organelles are “Small Organs,” which are subcellular structures that have specific functions in the cell.

• The nucleus is found in all eukaryotic cells and is double-membraned (porous) in structure. This is the largest organelle and the information repository. Additionally, this is the cell’s control center or mainly its brain.
  • This houses the nucleolus covered by the nuclear envelope and contains the chromosomes, thread-like structures that carry genes.
• The Endoplasmic Reticulum is a network of membranous canals filled with fluid. They help transport materials throughout the cell.
• The rough Endoplasmic Reticulum is involved in protein synthesis and comprises cisternae, tubules, and vesicles found all over the cell. Its rough name came from the ribosomes attached to its membrane surface.
• Smooth Endoplasmic Reticulum is the storage organelle and is the site for lipid synthesis, which also functions as the detoxifier of the cell.
• Mitochondria is known as the “powerhouse of the cell” because it produces adenosine triphosphate (ATP).
• Plastids (Present only in plant cells) are large membrane-bound organelles that contain pigments. Depending on their pigments, there are three types of plastids: Chloroplasts, Chromoplasts, and Leucoplasts.
• Ribosomes are the site for protein synthesis and are cytoplasmic organelles found near or attached to the rough endoplasmic reticulum.
• Golgi Apparatus, or the Golgi Complex, is a flattened membrane-bound organelle with stacked pounces called cisternae. This transports, modifies, and packages proteins to specific destinations.
• The cytoskeleton is the continuous network of structures present throughout the cytoplasm. This comprises different proteins, actin, and tubulin, to provide shape and mechanical resistance.
• Cilia and Flagella are hair-like structures outside the cell. This helps in the movement of the cell.
• The centrosome is composed of centrioles, which form spindle fibers during cell division and also form the bases of the cilia and flagella.
• Vacuoles are storage bubbles filled with fluid enclosed by a membrane found in the cell. This stores food and nutrients that the cell needs.

What is a human cell?

A Human Cell is the smallest functional unit of life. It comprises the tissues, organs, the organ system, and the human organism. Each of these cells contains genetic material that can replicate itself. They provide structure, take in nutrients, and transform them into energy, enabling our body to function.

The body comprises trillions of cells, each with a different function. The following are the various types of cells:

• Stem Cells are special cells that can turn into any cell.
• Bone cells form our bones and are of at least three main types: osteoclasts, osteoblasts, and osteocytes.
• Blood Cells transport nutrients and oxygen throughout the body. There are three types: red blood cells, white blood cells, and platelets.
• Female egg cells are the largest human cells essential for reproduction.
• Sperm Cells fertilize the ovum and are the smallest cells in the human body.
• Fat Cells, also known as adipocytes, are fats the body uses for energy.
• Muscle Cells, also called myocytes, are long tubular cells essential for movement, support, and internal functions.
• Nerve Cells, also known as neurons, are the body’s communication system, comprising two parts: the cell body and nerve processes–axons and dendrites.

How do cells work?

Cells metabolize food to energy and divide to produce more.

Cellular Metabolism consists of controlled biochemical reactions in a cell to maintain homeostasis. These processes are essential for organisms to grow and produce. It is divided into two processes: anabolic and catabolic.

• Anabolic Metabolism uses energy to form molecules like nucleic acids and enzymes to perform specific functions. There are three stages: production of precursors, activation into reactive forms, and assembly of precursors.
• Catabolic Metabolism is the breaking down of complex molecules. This serves as the source of energy and components to form anabolic reactions. This process is usually exothermic.

Cell Division is the formation of new cells from parent cells. The cell undergoes two types of cell division:

• Mitosis replicates one parent cell to two daughter cells, essential for growth and repair.
• Meiosis divides a parent cell into four genetically different daughter cells, which is significant in human reproduction.

Why do cells need water?

Water, the universal solvent, is essential for your body, especially your cells, to function correctly. Humans are composed of 70% water, which is a crucial component.

• It facilitates the transportation of nutrients inside the cell and the excretion of waste products outside through the osmosis process from low to high concentrations.
• Additionally, water is a small and fast molecule, so it acts as a lubricant when large-scale motions are needed to move large molecules.

Are all cells alive?

Being alive, by definition, is anything that grows, moves, reproduces, and respires are considered to be living. A cell functions the same way. As cells are the smallest fundamental life unit, all cells are considered alive.

All living organisms are made from cells, from the only unicellular organisms to the trillions of multicellular beings.

How long do cells live?

The majority of the cells eventually die, but not all. On average, cells in your body live up to 7 to 10 years. The lifespan of cells differs depending on the type of cell.

Commonly known cells’ lifespans:

• Nerve cells stay alive for the rest of a person’s life.
• Heart muscle cells live up to forty years, regenerating in limited amounts.
• White blood cells live for around two weeks.
• Red blood cells live for about four months.
• Liver Cells can live up to eighteen months.
• Epidermal Cells live up to two weeks.
• Fat Cells live around eight years.
• Egg Cells up to fifty years.

What happens when a cell dies?

Cell death happens when cells in your body stop working and die. As cells perish because of cell division, they are recycled to produce new, efficient ones. It is already established that each cell has its lifespan. Thus, natural cell death is essential for keeping your body healthy.

There are three types of cell death:

• Apoptosis happens naturally when a cell needs to self-destruct or die. This usually occurs when maximum cell division is achieved.
• Autophagy is another form of programmed cell death, which occurs when your body is experiencing stress or hunger. It reuses old cell parts to make new ones.
• Necrosis is an unexpected death due to the lack of blood flow, leading to tissue death. This also happens when people are deceased.

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