Lecture 10: Enzyme introduction

Question 1

How do enzymes increase the rate of reaction?

Answer 1

• by lowering the activation energy

- by increasing the frequency of which molecule come close together in the right orientation

Question 2

What are the two models of enzyme substrate binding?

Which model is considered correct?

Answer 2

• The lock and key model
• The induced fit model
• The induced fit model is accepted as the change in shape allows bonds to be broken and formed

Question 3

What happens to the enzyme in the lock and key model?

Answer 3

The enzyme doesn’t move and substrate molecule fits perfectly into the active site of the enzyme

Question 4

What happens to the enzyme in the induced fit model?

How does this lead to an enzyme conformation change ?

Answer 4

The enzyme moves to make the substrate fit in its active site

• Interaction btw enzyme and substrate leads to a conformation change - enzyme changes shape
• Conformation change generates complementary fit btw enzyme and substrate; enzyme wraps around substrate and you get an induced perfect fit

Question 5

How does an enzyme and substrate interact?

Answer 5

• Substrate binds to the active site through non-covalent interactions
• interactions are specific
• Binding leads to the formation of a transition state (T)
• Formation of (T) requires less energy, reducing the activation energy to allow the reaction to go faster

Question 6

What are the major catalytic mechanisms?

Answer 6

1. Acid-base catalysis
2. Covalent catalysis
3. Metal ion cataylsis

Question 7

What is acid-base catalysis?

Answer 7

It involves the transfer H+

- Side chains at the active site may be ionisable, which allows them to take up or donate protons

Question 8

What is covalent catalysis?

Answer 8

It involves the formation of a highly reactive short-lived intermediate which is COVALENTLY attached to the enzyme

Question 9

What is metal ion catalysis?

Answer 9

This is where the reaction centre has a metal ion - metal ions are COFACTORES
1/3 of enzymes require metal ions for catalytic activity as metal ions provide:
- Substrate orientation
- Binding energy
- Sites for oxidation-reduction reactions

Question 10

What are cofactors?

What are coenzymes

Answer 10

Cofactors
- are inorganic molecules which aid in the reaction and are unchanged e.g metal ion

Coenzymes
- Are small organic molecules which are derived from vitamins. They function as carries and are changed during the reaction