1.4Unit 1 — Cell Biology
Proteins and Enzymes — SQA National 5 Biology — SQA National 5 Biology Revision Notes & Topical Questions
5 min read 2 parts Lesson 4 of 6
Section 1 of 2Functions of proteins (SHARE)
| Protein Function | Description | Specific Examples |
|---|---|---|
| S — Structural | Provide physical support and strength to cells and tissues | Collagen (skin, bone), Keratin (hair, nails) |
| H — Hormones | Chemical messengers transported in blood to target organs | Insulin (regulates blood glucose), Glucagon |
| A — Antibodies | Y-shaped defence proteins produced by white blood cells (B-lymphocytes) | Immunoglobulins binding to specific pathogen antigens |
| R — Receptors | Membrane proteins receiving external chemical signals | Hormone receptors, neurotransmitter receptors on synapses |
| E — Enzymes | Biological catalysts that speed up biochemical reactions in cells | Amylase, Catalase, Pepsin, DNA polymerase |
Section 2 of 2Enzyme action and specificity
1Biological catalysts2 points
:
- Speed up chemical reactions in living cells while remaining chemically unchanged.
- Each enzyme is specific to one substrate because its active site has a complementary shape to that substrate ("Lock and Key" hypothesis).
2Types of enzyme reactions2 points
:
- Degradation (breakdown)Large complex molecule broken into smaller products. Example: Hydrogen peroxide → (Catalase) → Oxygen + Water (HPCOW); Starch → (Amylase) → Maltose (SAM).
- Synthesis (build up)Small molecules joined together into a larger product. Example: Glucose-1-phosphate → (Phosphorylase) → Starch (G-1-P P Starch).
3Factors affecting enzyme activity2 points
:
- Optimum conditionsThe temperature and pH at which an enzyme is most active (highest reaction rate). Human enzymes typically have an optimum temperature of ~37 °C.
- DenaturationAt temperatures well above the optimum (e.g. > 50 °C) or extreme pH levels, the delicate bonds maintaining the enzyme's 3D structure break.
- The active site permanently changes shape; the substrate can no longer fit, and catalytic activity is irreversibly lost.
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