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B1: Biological Molecules and Enzyme Kinetics

Year 1 / ASYear 2 / A-Level All Boards (AQA, Edexcel, OCR, WJEC, CCEA) AQA

Carbohydrates, lipids, proteins, nucleic acids, ATP, enzyme kinetics, competitive and non-competitive inhibition.

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πŸ“‹ Key Definitions and Core Concepts

Induced Fit Model: Substrate binding causes conformational change in enzyme's active site, lowering activation energy.
Primary Structure: Unique sequence of amino acids linked by covalent peptide bonds in a polypeptide.

πŸ” Key Principles & Specification Requirements

  • Condensation joins monomers releasing Hβ‚‚O; hydrolysis breaks bonds using Hβ‚‚O.
  • Starch (amylose/amylopectin) and glycogen store glucose in compact, insoluble granules.
  • Competitive inhibitors increase K_m without changing V_max; non-competitive inhibitors reduce V_max.

πŸ’‘ Worked Example Question

Exam-Style Question

Question:

Explain how glycogen structure relates to its storage function in animal liver and muscle cells.

Model Solution & Mark Scheme:

1. Ξ±-glucose polymer: easily hydrolysed to release glucose for respiration.
2. Highly branched (1,6-glycosidic bonds): multiple terminal ends for rapid simultaneous enzymatic cleavage.
3. Insoluble: does not alter cellular osmotic potential.
4. Compact helical structure: maximizes energy storage density.

❓ Practice Questions & Mark Schemes

Q1: Describe the non-reducing sugar biochemical test.

Show Model Answer

Answer: Boil sample with dilute HCl to hydrolyse glycosidic bonds, neutralise with NaHCO₃, re-test with Benedict's reagent; brick-red precipitate indicates positive result.

Q2: Contrast competitive and non-competitive enzyme inhibitors.

Show Model Answer

Answer: Competitive bind active site reversibly (overcome by high [S]); non-competitive bind allosteric site altering 3D conformation (lowers V_max).

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