Introduction to enzymes

Question 1

What are enzymes (2)

Answer 1

1. Globular proteins that catalyse reactions of ‘substrates’
2. Required for almost all biochemical reactions within cells

Question 2

What do enzymes have (5)

Answer 2

1. An active site that binds the substrate, prior to the reaction
2. High efficiency
3. High chemical and stereo-specificity
4. pH optima
5. Temperature optima

Question 3

What is the mechanism of action of enzymes ()

Answer 3

1. Enzyme + substrate + ES
2. ES → EP
3. EP → E + P

Question 4

What is Ks (4)

Answer 4

1. The dissociation constant of ES
2. Ks = [E][S]/[ES]
3. Same units as concentration (mM)
4. Strong binding = High (ES) and low Ks

Question 5

What happens when a substrate binds to the active site (5)

Answer 5

1. Substrate converted to product by chemical change
2. No covalent bonding between enzyme and substrate
3. No covalent bond with enzyme means no chemical change to the enzyme
4. Intermolecular forces between enzyme and substrate
5. Substrate changes form whilst connected to enzyme then there is a dissociation

Question 6

What happens to the equilibrium position with catalysts (3)

Answer 6

1. Position (left/right) is not affected by enzyme
2. Reduced time to reach equilibrium position with enzyme
3. Both forward and backwards reaction rates are increased.

Question 7

What are the classifications of enzymes (6)

Answer 7

1. Oxidoreductase - oxidation/reduction
2. Transferase
3. Hydrolases - hydrolysis
4. Lyases - Split molecules
5. Isomerases
6. Ligases - Join molecules

Question 8

What are co-factors (2)

Answer 8

1. non-proteins that many enzymes require in order to work and allow organisms to regulate enzymatic action.
2. Some cofactors are small organic molecules called coenzymes (ATP, Vit B1, Vit C)

Question 9

How can bonds between enzyme and substrate be described

Answer 9

Not always covalent - e.g. H-bonds

Question 10

What are electrostatic reactions (3)

Answer 10

1. Between positive and negative charges.
2. Charges can be full (+/-) or partial (d+/ d-).
3. Hydrophobic bonds
   occur between non-polar regions (e.g. hydrocarbons).