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

What term describes the ability of certain substrates to fit only with specific enzymes?

1. Specificity

2. Substrate affinity

3. Enzyme concentration

4. Reaction rate

The correct answer is: Specificity

The term that describes the ability of certain substrates to fit only with specific enzymes is specificity. In biochemistry, enzymes are highly selective catalysts, meaning they interact with specific substrates that match their active site. This matching is essential for the enzyme's function because it ensures that only the desired reaction occurs. Each enzyme has a unique shape and property that corresponds to a particular substrate, enhancing the efficiency of biochemical reactions within the organism. Substrate affinity refers to how tightly an enzyme binds to its substrate, which plays a role in the rate of reaction but does not define the selectivity process itself. Enzyme concentration measures the amount of enzyme present, affecting reaction rates but not the relationship between specific substrates and enzymes. Reaction rate describes how quickly a reaction proceeds and is influenced by various factors, including enzyme concentration and substrate availability, rather than the selectivity of enzyme-substrate interactions. Thus, specificity is the most accurate term to describe the unique fit between certain substrates and their corresponding enzymes.