3. Enzymes

3.1 Mode of action of enzymes

There are many different enzymes, each one specific to a particular reaction. This specificity is the key to understanding the efficient functioning of cells and living organisms.

  1. state that enzymes are globular proteins that catalyse reactions inside cells (intracellular enzymes) or are secreted to catalyse reactions outside cells (extracellular enzymes)

  2. explain the mode of action of enzymes in terms of an active site, enzyme–substrate complex, lowering of activation energy and enzyme specificity, including the lock-and-key hypothesis and the induced-fit hypothesis

  3. investigate the progress of enzyme-catalysed reactions by measuring rates of formation of products using catalase and rates of disappearance of substrate using amylase

  4. outline the use of a colorimeter for measuring the progress of enzyme-catalysed reactions that involve colour changes

Introduction to A Level Enzymes

3.1 Enzyme structure and mode of action

Mechanisms of enzyne reactions

3.2 Factors that affect enzyme action

  1. investigate and explain the effects of the following factors on the rate of enzyme-catalysed reactions:

• temperature

• pH (using buffer solutions)

• enzyme concentration

• substrate concentration

• inhibitor concentration

  1. explain that the maximum rate of reaction (Vmax) is used to derive the Michaelis–Menten constant (Km), which is used to compare the affinity of different enzymes for their substrates

  2. explain the effects of reversible inhibitors, both competitive and non-competitive, on enzyme activity

  3. investigate the difference in activity between an enzyme immobilised in alginate and the same enzyme free in solution, and state the advantages of using immobilised enzymes

3.2 Factors affecting enzyme action

Enzyme inhibitors

Enzymes Study Club

Enzyme past paper questions explained

Immobolised enzymes