Enzymes

You will be able to

• Explain the mode of action of an enzyme in terms of its active site, the enzyme–substrate complex, the lowering of activation energy and specificity.
• Compare the lock-and-key and induced-fit hypotheses, and predict whether a molecule of a given shape will react.
• State that enzymes are globular proteins that act inside cells (intracellular) or are secreted to act outside them (extracellular).

You will be able to

• Describe how to follow an enzyme reaction by the rate of formation of a product (catalase) and the rate of disappearance of a substrate (amylase), including with a colorimeter.
• Determine an initial rate from the gradient of a tangent at t = 0, and calculate a mean from repeats.
• Explain the effects of temperature, pH and enzyme concentration on the rate, distinguishing denaturation from inactivity at low temperature and rate from final yield.

You will be able to

• Explain the effect of substrate and enzyme concentration on the rate in terms of active sites becoming saturated.
• Determine Vmax and Km from a graph of rate against substrate concentration, and use Km to compare the affinity of enzymes for their substrates.
• Explain how reversible competitive and non-competitive inhibitors reduce enzyme activity, and predict whether extra substrate overcomes each.

You will be able to

• Compare the activity of an enzyme immobilised in alginate with the same enzyme free in solution, and explain why the immobilised enzyme is slower at first.
• Explain the effect of bead size on the rate in terms of surface area to volume ratio and diffusion distance.
• State the advantages of immobilised enzymes: easy separation, a product free of enzyme, reuse and often greater stability.