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

What effect does pH have on enzymes?

1. Extreme pH levels can denature enzymes by altering their shape

2. Enzymes are not affected by pH changes

3. pH only affects enzyme activity at very high concentrations

4. All enzymes function optimally at a pH of 7

The correct answer is: Extreme pH levels can denature enzymes by altering their shape

Enzymes are biological catalysts that speed up chemical reactions in living organisms, and their activity is highly sensitive to changes in pH. The correct answer states that extreme pH levels can denature enzymes by altering their shape. This is accurate because enzymes have an optimal pH range in which they function effectively. When the pH falls outside this range, the hydrogen and hydroxide ions in the solution can disrupt the hydrogen bonds and ionic bonds that maintain the enzyme's three-dimensional structure. This disruption alters the shape of the enzyme, particularly at the active site where substrate molecules bind, which impairs its ability to catalyze reactions. In contrast, the other choices are inconsistent with our understanding of enzymatic function. Enzymes are indeed affected by pH changes; pH does not exclusively impact enzyme activity at very high concentrations; and while many enzymes do have an optimal activity at around pH 7, this is not true for all enzymes, as each enzyme has a specific pH at which it works best depending on its environment and function.