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

Why do different enzymes produce different shapes on a reaction rate graph?

1. They react to different temperatures

2. They have different structures and functions

3. They are affected by different pH levels

4. They work at varying concentrations

The correct answer is: They have different structures and functions

Different enzymes produce different shapes on a reaction rate graph primarily because they have different structures and functions. Each enzyme is a unique protein with a specific active site that is complementary to its substrate. The variation in the structure of enzymes leads to differences in how they facilitate reactions, including their efficiency and the conditions under which they operate optimally. For instance, the shape of the graph can reflect how quickly the enzyme converts substrate to product, which can differ based on the enzyme's intrinsic properties, such as how tightly substrates bind to the active site or how the enzyme changes its shape during the reaction (a process known as induced fit). These structural differences determine not only the rate at which reactions occur but also how enzymes respond to changes in factors like temperature and pH, ultimately shaping the resulting graph for the reaction rate. Other choices may reference important factors that do affect enzyme activity, such as temperature and pH levels. However, the underlying reason for the differences in graphs primarily stems from the inherent structural variations among different enzymes and their corresponding functions in catalyzing specific reactions.