Class 12 Chemistry Chapter 10 Biomolecules – Revision Notes

Quick revision notes for Class 12 Chemistry Chapter 10 – Biomolecules, covering carbohydrates, proteins, enzymes, vitamins, nucleic acids and hormones. Ideal for last-minute board exam revision.

Last Updated: September 23, 2026

Carbohydrates

Carbohydrates are optically active polyhydroxy aldehydes (aldoses) or polyhydroxy ketones (ketoses), and their derivatives. Classified by hydrolysis behaviour: monosaccharides (cannot be hydrolysed further, e.g. glucose, fructose, ribose), oligosaccharides (hydrolyse to 2–10 monosaccharide units — disaccharides, e.g. sucrose, maltose, lactose, are the most common case), and polysaccharides (hydrolyse to many monosaccharide units, e.g. starch, cellulose, glycogen). Glucose exists mainly as a six-membered pyranose ring formed by cyclisation at C5, giving α and β anomers that interconvert via mutarotation (equilibrium rotation +52.5°). Fructose forms a five-membered furanose ring. Sucrose hydrolyses to glucose+fructose (non-reducing; hydrolysis product is called invert sugar); maltose hydrolyses to glucose+glucose (reducing, α-1,4 link); lactose hydrolyses to glucose+galactose (reducing, β-1,4 link). Starch = amylose (unbranched, α-1,4, helical, blue with iodine)+amylopectin (branched, α-1,6 branch points); cellulose is an unbranched β-1,4-glucose polymer (structural, non-digestible by humans); glycogen is the animal storage polysaccharide, more highly branched than amylopectin.

Proteins

Proteins are polymers of α-amino acids joined by peptide linkages (–CO–NH–). Amino acids are classified as essential (must come from diet, e.g. valine, leucine) or non-essential (body can synthesise, e.g. glycine, alanine), and exist as zwitterions in solution, giving them amphoteric behaviour. Protein structure has four levels: primary (amino acid sequence), secondary (α-helix or β-pleated sheet, stabilised by hydrogen bonding between peptide linkages), tertiary (overall 3-D folding, stabilised by hydrogen bonds, disulphide bonds, van der Waals forces and electrostatic interactions), and quaternary (assembly of multiple polypeptide subunits, e.g. haemoglobin). Fibrous proteins (parallel chains, water-insoluble, e.g. keratin, myosin) differ from globular proteins (coiled/folded, water-soluble, e.g. insulin, albumin). Denaturation destroys secondary/tertiary structure and biological activity (heat, pH change) while leaving the primary structure intact — e.g. coagulation of egg white, curdling of milk.

Enzymes

Enzymes are biological catalysts, almost always globular proteins, that catalyse biochemical reactions with high specificity under mild physiological conditions.

Vitamins

Classified by solubility into fat-soluble (A, D, E, K — stored in liver/adipose tissue) and water-soluble (B-complex and C — not stored, except B₁₂). Key deficiency diseases: Vitamin A→night blindness; B₁ (thiamine)→beriberi; B₂ (riboflavin)→cheilosis; B₆ (pyridoxine, old name adermin)→convulsions; B₁₂ (cobalamin)→pernicious anaemia; C (ascorbic acid)→scurvy; D (calciferol)→rickets (children)/osteomalacia (adults); E (tocopherol)→increased RBC fragility, muscular weakness; K (phylloquinone)→increased blood-clotting time.

Nucleic Acids

Nucleic acids are biopolymers of nucleotides (nitrogenous base+pentose sugar+phosphate group); a nucleoside is just base+sugar. DNA: sugar is β-D-2-deoxyribose; bases are adenine, guanine, cytosine, thymine; usually a double helix of two complementary, antiparallel strands held by base pairing (adenine–thymine via 2 H-bonds, guanine–cytosine via 3 H-bonds); carries and transmits hereditary information and can self-replicate. RNA: sugar is β-D-ribose; bases are adenine, guanine, cytosine, uracil (in place of thymine); usually single-stranded; directs protein synthesis via three types — m-RNA (carries the genetic code from DNA to the ribosome), t-RNA (carries specific amino acids to the ribosome), and r-RNA (structural/catalytic component of the ribosome).

Hormones

Hormones are chemical messengers secreted by endocrine glands that regulate the body’s metabolic activities. They fall into three broad chemical classes: steroid hormones (e.g. estrogen, progesterone, testosterone), polypeptide hormones (e.g. insulin), and amino-acid-derivative hormones (e.g. epinephrine/adrenaline, thyroxine). Insulin, secreted by the pancreas, regulates blood glucose levels; its deficiency causes diabetes.

Written by Satish

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