Enzymes

Question 1

How do enzymes specify a chemical reaction?

Answer 1

1. Site of occurrence - location (intracellular/extracellular)
2. Rate of reaction - amount of active enzyme present
3. Reaction time - state (active/inactive)

Question 2

What are the 2 enzymes responsible for synthesis and degradation of acetylcholine?

Answer 2

ChAT: for synthesis (acetyl CoA +Choline -> Ach + CoA)
AChE: for degradation (Ach + H2O -> Choline + acetic acid)

Question 3

Sites present on an enzyme

Answer 3

1. Active site - binding of substrate
2. Binding site - for coenzyme/cofactor
3. Regulatory site - for activator/inhibitor
4. Catalytic site - provide chemical environment

Question 4

2 ways for an enzyme to function as a catalyst

Answer 4

1. Provide alternative pathway with lower activation energy
2. Mechanical straining of molecule in catalytic site
   - > change shape to facilitate change of structure
   - > accounts for the specificity of enzyme

Question 5

Ways of changing accessibility of enzyme

Answer 5

Introduce small structural changes
1. Phosphorylation - fast, reversible
2. Cleavage of peptide bond - fast, irreversible
3. Activating/Inactivating enzyme - by activator/inhibitor
Adjust total amount of enzyme
4. Change rate of synthesis and degradation - slow, irreversible (long-term regulation)`

Question 6

What is positive influence? When does it occur? What curve would it demonstrate on graph?

Answer 6

Occurs on oligomeric enzyme with multiple subunits

• > bound subunit can exert positive influence on neighbouring subunits to increase the affinity of substrate
• Sigmoidal curve*

Question 7

What do allosteric regulators do?

Answer 7

+ allosteric regulators:
put oligomeric enzyme in active site -> demonstrate more sigmoidal curve
- allosteric regulators:
less sigmoidal curve, lengthens initial phase