Chemical Constituents of Living Cells: Biomolecules

Life is a complex series of chemical reactions, and biomolecules are the dancers. Biomolecules are organic compounds present in living organisms that are necessary for cellular metabolism, growth, and maintenance of the life lottery. The focus of this guide is to outline the four basic forms of biomolecules: carbohydrates, proteins, lipids, and nucleic acids, along with their important biological functions.

1.0Introduction

• Biomolecules are complex organic molecules composed of simpler, repeating units known as monomers. When extensive groups of monomers join together, they generate a polymer. 
• The process of polymerization is essential for the structure and function of all the major biomolecules. 
• Although there are countless organic molecules, the biomolecules that are necessary for life are classified into four types.

2.0Carbohydrates: The Energy Providers 

• Carbohydrates are Earth's most abundant organic compounds, including carbon, hydrogen, and oxygen, usually in a 1:2:1 ratio. 
• Their main purpose is to offer fast energy for cellular processes. They also can be used as structural components.
• Monosaccharides: These are the simplest sugars and the building blocks of all carbohydrates. Examples include glucose (the primary energy source for cells), fructose (found in fruits), and galactose.
• Disaccharides: Formed when two monosaccharides are linked together. Common examples are sucrose (table sugar, made of glucose and fructose) and lactose (milk sugar, made of glucose and galactose).
• Polysaccharides: Long chains of monosaccharides. They can be for energy storage or structural support.
• Starch: The primary energy storage polysaccharide in plants.
• Glycogen: The energy storage polysaccharide in animals, stored mainly in the liver and muscles.
• Cellulose: A major structural component of plant cell walls. It provides rigidity and is indigestible by most animals.

3.0Proteins: The Workhorses of the Cell 

Proteins are the most versatile biomolecules. They are polymers of amino acids linked by peptide bonds. There are 20 different common amino acids, and the sequence in which they are arranged determines the protein's unique 3D structure and function.

Proteins perform a vast array of functions:

• Enzymes: Act as biological catalysts, speeding up chemical reactions without being consumed.
• Structural proteins: Provide support, like collagen in skin and keratin in hair and nails.
• Transport proteins: Carry molecules, such as haemoglobin, which transports oxygen in the blood.
• Hormones: Act as chemical messengers, like insulin, which regulates blood sugar.
• Antibodies: Part of the immune system, they fight off infections.

4.0Lipids: The Energy Stores and More 

• Lipids are a diverse group of biomolecules that are insoluble in water. 
• They are primarily composed of carbon and hydrogen. 
• Their main functions include long-term energy storage, insulation, and the formation of cell membranes.
• Fats and Oils: Composed of a glycerol molecule and three fatty acid chains. Fats are solid at room temperature (e.g., butter), while oils are liquid (e.g., olive oil). They are a highly efficient form of energy storage.
• Phospholipids: Key components of the cell membrane. They have a hydrophilic (water-loving) head and two hydrophobic (water-fearing) tails, allowing them to form a bilayer that separates the cell's interior from the external environment.
• Steroids: Lipids with a four-ring structure. Examples include cholesterol, which is crucial for membrane fluidity and a precursor to hormones such as testosterone and estrogen.

5.0Nucleic Acids: The Genetic Blueprint 

• Nucleic acids are the information-carrying biomolecules of the cell. 
• They are polymers of nucleotides. Each nucleotide consists of a phosphate group, a five-carbon sugar, and a nitrogenous base.

The two main types are:

• Deoxyribonucleic acid (DNA): The genetic material in most organisms. It contains the instructions for making proteins and is responsible for heredity. DNA forms a characteristic double helix structure.
• Ribonucleic acid (RNA): Plays a crucial role in translating the genetic information from DNA into proteins. Different types of RNA (mRNA, tRNA, rRNA) are involved in this process.