Biomolecules – Study Notes for NEET (Medical)
1. Simple Explanation
Biomolecules are the building blocks of life. They are organic molecules that perform structural, storage, transport, catalytic, and regulatory roles in living organisms. In biology, the four main classes are:
| Class | Key Functions | Representative Molecules |
|---|---|---|
| Carbohydrates | Energy source & structural support | Glucose, starch, cellulose |
| Lipids | Energy storage, membrane structure, signalling | Triglycerides, phospholipids, cholesterol |
| Proteins | Enzymes, structure, transport, defence, signalling | Hemoglobin, collagen, antibodies |
| Nucleic Acids | Store & transfer genetic information | DNA, RNA |
2. Key Points
2.1 Carbohydrates
| Feature | Detail |
|---|---|
| Monosaccharides | Simple sugars (glucose, fructose, galactose). |
| Disaccharides | Glucose + galactose = lactose. |
| Polysaccharides | Storage (starch, glycogen) & structural (cellulose, chitin). |
| Functional groups | Aldoses (–CHO at C-1) vs ketoses (C=O at C-2). |
| Energy yield | 1 Glucose → 30–38 ATP (via glycolysis, TCA, OXPHOS). |
| Important pathways | Glycolysis, gluconeogenesis, glycogenolysis. |
2.2 Lipids
| Sub‑class | Structure | Function |
|---|---|---|
| Fatty Acids | Hydrocarbon chain + carboxyl group | Energy storage, precursors to signalling molecules |
| Triglycerides | 3 fatty acids + glycerol | Long‑term energy storage |
| Phospholipids | 2 fatty acids + glycerol + phosphate + head group | Bilayer formation (cell membranes) |
| Steroids | Four‑ring core (cholesterol) | Hormones, membrane fluidity |
| Eicosanoids | Derived from arachidonic acid | Inflammation, platelet aggregation |
2.3 Proteins
| Level | Description |
|---|---|
| Primary structure | Linear sequence of amino acids (20 standard). |
| Secondary structure | α‑helix & β‑sheet via hydrogen bonds. |
| Tertiary structure | 3‑D folding driven by hydrophobic, ionic, hydrogen interactions. |
| Quaternary structure | Assembly of multiple polypeptide chains. |
Functional properties
- Enzymes: Catalysis, active site specificity.
- Structural: Collagen, keratin.
- Transport: Hemoglobin, albumin.
- Immune: Antibodies, cytokines.
- Signalling: Hormones (insulin, growth hormone).
Post‑translational modifications – phosphorylation, glycosylation, ubiquitination.
2.4 Nucleic Acids
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Nitrogenous bases | A, T, G, C | A, U, G, C |
| Strand | Double helix (antiparallel) | Single strand (mRNA, tRNA, rRNA) |
| Functions | Store hereditary information | Gene expression, catalysis (ribozyme), regulation |
Key processes
- Replication – Semi‑conservative; DNA polymerases.
- Transcription – RNA polymerase synthesises mRNA.
- Translation – Ribosomes decode mRNA into polypeptide.
2.5 Vitamins & Cofactors
- Fat‑soluble: A, D, E, K – stored in liver/adipose; involved in vision, bone health, antioxidant, clotting.
- Water‑soluble: B‑complex (coenzymes for metabolism), C – antioxidant.
2.6 Hormones (Biomolecule‑based signalling)
- Water‑soluble: Peptide (insulin), catecholamines (adrenaline).
- Lipid‑soluble: Steroids (cortisol), thyroid hormones (T₃/T₄).
3. Worked Example – Glycolysis (Glucose → Pyruvate)
| Step | Substrate | Enzyme | Product | ATP/NAD⁺ Change |
|---|---|---|---|---|
| 1 | Glucose | Hexokinase | Glucose‑6‑P | -1 ATP |
| 2 | Glucose‑6‑P | Phosphoglucose isomerase | Fructose‑6‑P | |
| 3 | Fructose‑6‑P | Phosphofructokinase‑1 | Fructose‑1,6‑BP | -1 ATP |
| 4 | Fructose‑1,6‑BP | Aldolase | Glyceraldehyde‑3‑P + DHAP | |
| 5 | DHAP | Triose phosphate isomerase | Glyceraldehyde‑3‑P |