Scheme of Work Cambridge International as & a level

Extension activity: Provide an opportunity for learners to suggest why certain factors affect enzyme activity, and examples of enzymes that have unusual optimum values (e.g. Taq DNA polymerase and human pepsin). An accessible research article is at:
www.nature.com/news/1998/980917/full/news980917-7.html

3.2.2 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. 3.2.3 Explain the effects of reversible inhibitors, both competitive and non-competitive, on enzyme activity.

Host a class discussion to explain the concept of enzyme affinity, and how this can be quantified by reference to the Michaelis–Menten constant (Km). To extend their understanding, learners construct Venn diagrams to summarise the differences between inhibitors. To do this, learners draw a circle labelled ‘competitive inhibitors’ overlapping with another circle labelled ‘non-competitive inhibitors’. Properties that they have in common (e.g. both reduce the ability for an enzyme to bind to its substrate) can be listed in the overlapping area. Properties that are unique (e.g. effect on Km) can be listed separately. (I) Learners can carry out practical activities that focus on enzyme inhibition. However, the results are usually quite unreliable. One exception is the effect of phosphate on phosphatase: www.saps.org.uk/attachments/article/106/SAPS%20-%20Enzyme%20inhibition%20-%20the%20effect%20of%20phosphate%20on%20phosphatase%20-%20Student%20Guide.doc Extension activity: Learners carry out research to list medicinal drugs that rely on enzyme inhibition.

3.2.4 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.

Resource Plus Carry out the Immobilising enzymes experiment referring to the Teaching Pack for lesson plans and resources. In this task, learners encapsulate the enzyme lactase in alginate beads and show that its ability to hydrolyse its substrate, lactose, is not affected by immobilisation. As part of the task, learners are challenged to suggest how the equipment is used to investigate the effect of changing an independent variable and are introduced to statistical tests and the idea of a hypothesis. Learners write the shortest paragraph possible using the following key terms: immobilised, affinity, continuous, yield. This is a good way to focus learners on developing their higher-order thinking skills to make sense of the meaning of these terms, rather than simply recall them. (F)