Rates of reaction, Vmax and Core Practical 4

Overview

Recall questions on measuring initial rate, the effect of enzyme and substrate concentration, Vmax, and the controls in Core Practical 4.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Define the initial rate of reaction.

   Model answer

   The initial rate of reaction is the rate measured at the very start of a reaction when substrate concentration is at its highest and product concentration is negligible.

2. 2

   Why is the initial rate of reaction measured at the very start of a reaction?

   Model answer

   Because substrate concentration is at its highest and product concentration is negligible, giving the most accurate measure of enzyme activity.

3. 3

   What effect does increasing enzyme concentration have on the initial rate of reaction when substrate is in excess?

   Model answer

   The initial rate of reaction increases proportionally with enzyme concentration.

4. 4

   Why does increasing enzyme concentration increase the initial rate of reaction?

   Model answer

   More enzyme molecules mean more active sites are available to form enzyme-substrate complexes per unit time, provided substrate is in excess.

5. 5

   Describe what happens to the initial rate of reaction as substrate concentration increases.

   Model answer

   The initial rate of reaction increases until all enzyme active sites are saturated, after which the rate plateaus.

6. 6

   Why does the rate of reaction plateau at high substrate concentrations?

   Model answer

   Because all enzyme active sites become saturated with substrate molecules, so adding more substrate cannot increase the rate further.

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