OCR General Certificate of Secondary Education (GCSE) Biology Practice Exam

In the lock and key model, what happens in stage one?

1. An enzyme-substrate complex is formed

2. Enzyme and substrate come into contact

3. The substrate is converted to product

4. The enzyme is released

The correct answer is: Enzyme and substrate come into contact

In the lock and key model of enzyme action, the first stage involves the enzyme and substrate coming into contact with one another. This initial interaction is crucial because it sets the stage for the subsequent steps in the reaction process. In this model, the substrate fits perfectly into the active site of the enzyme, much like a key fits into a lock. This correct fit is essential for the formation of the enzyme-substrate complex, which will lead to the further transformation of the substrate into product, as described in later stages of the process. Understanding this stage helps illustrate how enzymes specifically recognize their substrates, highlighting the enzyme’s specificity and the importance of molecular interactions in biological reactions.