Explain the lock and key model of enzyme action, including how they are denatured. [6 marks]

The first step is to read the question and ensure that the student understands all of the terminology. For example, make sure the student knows what is meant by ‘explain’, ‘enzyme’, and ‘denatured’. Then the general concept of the lock and key model should be explained, to ensure that the student understands.Then the answer to the question should be written, taking into account the number of marks that is available, as this indicates how long the answer should be.ANSWER:In this model, the key represents the enzyme and the lock represents the substrateThe lock and key are specific for each other, and will only work together if the shapes are complementary. This applies to enzymes and substratesExtreme changes in pH or temperature denature enzymesWhen an enzyme is denatured it alters the shape of the active siteTherefore the active site is no longer complementary to the shape of the substrateSo the lock and key no longer fit together