Activation energy and models of enzyme action

Overview

Term activation energy, lock and key hypothesis of enzyme action and induced fit hypothesis of enzyme action.

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 term activation energy.

   Model answer

   Activation energy is the minimum energy that reacting molecules must possess before a reaction can take place.

2. 2

   How does an enzyme increase the rate of a reaction?

   Model answer

   It provides an alternative route with a lower activation energy, so a much greater proportion of molecules have enough energy to react.

3. 3

   Explain why lowering the activation energy allows reactions to run at body temperature.

   Model answer

   With a lower energy barrier, enough molecules reach the required energy at 37 °C, so heating the cell is unnecessary.

4. 4

   Describe how forming an enzyme–substrate complex helps break a bond in the substrate.

   Model answer

   Binding holds the substrate in a strained position that distorts and weakens the bond, so less energy is needed to break it.

5. 5

   How does an enzyme help two substrate molecules to join?

   Model answer

   The active site holds both substrates close together in the correct orientation, so they no longer have to collide by chance at the right angle.

6. 6

   Does an enzyme change the overall energy released by a reaction?

   Model answer

   No, the enzyme changes only the activation energy, so the energy difference between reactants and products is unaffected.

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