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Molecular Basis of Biological Processes

Introduction to Biomacromolecules

Introduction

All living organisms depend on large, complex molecules that perform and regulate nearly every biological process within the cell. These molecules are known as biomacromolecules, “bio” referring to their biological origin and “macromolecule” indicating their large molecular size. They are essential for life because they form the structural framework of cells, store and transfer information, and participate in countless chemical reactions that sustain growth, reproduction, and metabolism.

Although diverse in structure and function, biomacromolecules can be grouped into four main classes: carbohydrates, lipids, proteins, and nucleic acids. Each class has unique building blocks, specific roles, and characteristic chemical properties that together make life possible.

Carbohydrates (Polysaccharides)

Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, usually in the ratio Cₙ(H₂O)ₙ. They are the most abundant biomolecules on Earth and serve as both energy sources and structural materials in living organisms.

Their simplest units are monosaccharides, or simple sugars, such as glucose and fructose. These can join to form disaccharides (e.g., sucrose) and long chains called polysaccharides, such as starch, glycogen, and cellulose.

  • In animals, carbohydrates mainly function as quick sources of energy, as seen with glucose metabolism.
  • In plants, polysaccharides such as cellulose provide mechanical strength to cell walls, giving rigidity and protection.

Thus, carbohydrates play dual roles, fueling biological activity and supporting structural integrity of organisms.

Lipids

Lipids are a broad group of hydrophobic molecules that include fats, oils, waxes, phospholipids, and steroids. They consist mainly of carbon and hydrogen atoms, which makes them insoluble in water but soluble in nonpolar solvents.

Lipids serve several vital functions:

  • Energy storage: Fats store more than twice as much energy per gram as carbohydrates.
  • Structural components: Phospholipids are key constituents of cell membranes, forming a bilayer that separates and protects the cell interior.
  • Signaling and regulation: Steroid molecules, such as cholesterol, testosterone, and estrogen, act as hormones that regulate metabolism and reproduction.

Because of their diverse structures and functions, lipids contribute not only to cellular energy balance but also to membrane dynamics and chemical communication within the body.

Proteins

Proteins are the most functionally diverse biomacromolecules in living organisms. They are polymers of amino acids linked by peptide bonds, forming long chains that fold into specific three-dimensional shapes. The shape of a protein determines its function.

Proteins carry out nearly all cellular activities:

  • Enzymatic function: Enzymes catalyze biochemical reactions, speeding them up while remaining unchanged.
  • Structural support: Proteins such as collagen (in connective tissues) and keratin (in hair and nails) give strength and stability to body structures.
  • Transport: Hemoglobin carries oxygen in the blood, while membrane proteins transport ions and molecules across cell membranes.
  • Defense and regulation: Antibodies protect against pathogens, and hormonal proteins like insulin help regulate metabolism.

Without proteins, the cell could neither maintain its structure nor perform the complex reactions necessary for life.

Nucleic Acids

Nucleic acids, DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), are the molecules responsible for storing, transmitting, and expressing genetic information.

Each nucleic acid is built from repeating units called nucleotides, which consist of a sugar, a phosphate group, and a nitrogenous base.

  • DNA contains the hereditary instructions that determine an organism’s traits and directs protein synthesis.
  • RNA acts as a messenger, carrying the genetic code from DNA and translating it into functional proteins during protein synthesis.

Together, DNA and RNA ensure the continuity of life by passing genetic information from one generation to the next and directing cellular functions.

Summary

In summary, biomacromolecules form the foundation of all biological systems.

  • Carbohydrates provide energy and structure.
  • Lipids ensure membrane integrity and energy storage.
  • Proteins perform catalytic, structural, transport, and regulatory roles.
  • Nucleic acids store and transmit genetic information.

The interplay of these four classes of macromolecules underlies every aspect of life, from metabolism and growth to reproduction and evolution.