Enzymes

Learning objectives

Classify enzymes as intracellular or extracellular globular proteins, and explain catalysis using the active site, enzyme–substrate complex, lowered activation energy, specificity, and the lock-and-key and induced-fit hypotheses.

Describe how to follow an enzyme-catalysed reaction by measuring product formed (oxygen released by catalase) or substrate remaining (starch digested by amylase, tested with iodine), and outline how a colorimeter tracks reactions that change colour.

Plan and explain experiments that vary temperature, pH (held with buffers), enzyme concentration, substrate concentration or inhibitor concentration and measure the initial rate, including the shapes of the resulting graphs.

Explain how Vmax and the Michaelis–Menten constant (Km) are obtained from a graph of rate against substrate concentration, and use Km to compare how strongly different enzymes bind their substrates (lower Km, higher affinity).

Explain how reversible competitive inhibitors, which compete for the active site, and non-competitive inhibitors, which bind elsewhere and change its shape, reduce enzyme activity, and whether adding more substrate overcomes each.

Compare the activity of an enzyme trapped in alginate beads with the same enzyme in free solution, and state why industry uses immobilised enzymes (reuse, easy separation from the product, greater stability).