Introduction to Biomolecules

Biochemistry is the branch of biology that studies the chemical composition of living cells and the chemical reactions and molecular changes that occur in plants, animals and micro-organisms. It gives us the molecular basis for cell communication, and for the chemistry of inheritance and of disease.

Every living cell is built from a protoplasm packed with chemical substances called biomolecules. When the tissue of any living organism is chemically analysed, only a handful of elements turn up again and again — carbon, hydrogen, nitrogen, oxygen, sulphur, calcium, phosphorus, magnesium and a few others — each present in a characteristic proportion per unit mass of tissue. These are grouped as:

• Prime elements (drawn mainly from air and water): Carbon (C), Hydrogen (H), Oxygen (O)
• Macro elements (needed in comparatively larger amounts): Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulfur (S)
• Trace elements (needed only in minute amounts): Boron (B), Chlorine (Cl), Zinc (Zn), Copper (Cu), Iron (Fe), Sodium (Na), Molybdenum (Mo), Nickel (Ni), Silicon (Si), Cobalt (Co)

Chemically, every living organism is built around three basic types of macromolecules, each a polymer made by joining together many small subunits called monomers:

• Polysaccharides (carbohydrates) — polymers of monosaccharides
• Polypeptides (proteins) — polymers of amino acids
• Polynucleotides (nucleic acids) — polymers of nucleotides

Alongside these macromolecules, the cell also contains lipids — water-insoluble compounds of comparatively small molecular weight — and secondary metabolites (alkaloids, phenolics, terpenoids, essential oils, toxins, lectins, etc.), which are not required for basic growth but serve specialised roles, particularly in plants. Biomolecules are broadly classed as organic (carbon-based: macromolecules and micromolecules) or inorganic (the mineral elements listed above).