3.1

Question 1

How do enzymes speed up reactions?

Answer 1

Enzyme speed up reactions by lowering the activation energy, without being used up in the process

Question 2

What is the activation energy?

Answer 2

The energy needed to start a reaction

Question 3

How is an enzyme-substrate complex made? 2 points

Answer 3

1)An enzyme and substrate/reactant bind together at the active site to form an enzyme-substrate complex.

2)The substrate molecule is held within the active site by bonds that temporarily form between certain amino acids of the active site and groups on the substrate molecule.

Question 4

Lock and key analogy?

Answer 4

The shape of the substrate (key) will only fit into the active site of a specific enzyme (lock). The substrate and active site match each other – they are complementary:
1. Structurally – the 3D structure of the active site is specific to the substrate
2. Chemically – substances that are not chemically attracted to the active site wont react

Question 5

Limitation of lock and key model?

Answer 5

Other molecules could bind to enzymes at sites other than the active site so this altered the activity of the enzyme

Question 6

The induced fit model?

Answer 6

The IF model suggests that the enzyme changes shape slightly to fit the substrate; the enzyme is flexible and moulds itself around the substrate
• As the enzyme changes its shape, it puts a strain on the substrate molecule
• This strain distorts a particular bond which lowers the activation energy needed to break
the bond

Question 7

Why is the induced fit model a better observation of how enzymes work?

Answer 7

Because it explains how other molecules can affect enzyme activity and how the activation energy is lowered