MB - Metabolic Control via Enzyme Regulation I

Question 1

What is a metabolic pathway?

Answer 1

The enzymatic route that a metabolite molecule takes

Question 2

What are the rate-limiting steps of a metabolic pathway?

Answer 2

1. Slowest reaction in the pathway
2. Usually the first unique enzyme in a pathway

Question 3

What are 3 ways to identify the RLS?

Answer 3

1) Measure Vmax for enzymes in a pathway
* Lowest- RLS

2) Compare Keq and mass action ratios
* MAR is usually 100-1000 times < Keq for RLS

3) Test if step is at crossover point

Question 4

What 2 enzymes are of regulatory importance in glycolysis?

Answer 4

1. Hexokinase
2. Phosphofructokinase-1

Question 5

What is the need for metabolic control? (3)

Answer 5

• Ensures a given metabolic pathway is active when its product is needed
• Ensures competing pathways aren’t simultaneously active
• Ensures co-ordinated activity in multiple related pathways

Question 6

What are the 3 types of enzyme regulation?

Answer 6

1) Intrinsic control by metabolites- Allosterism/Inhibitors

2) Fast extrinsic control via hormones- Covalent modification (phosphorylation)

3) Slow extrinsic control via hormones- Gene expression

Question 7

What is product inhibition?

Answer 7

The product acts to inhibit the enzyme making it
* e.g G-6-P inhibits its own production in glycolysis (Hexokinase)

Question 8

What is allosterism?

Answer 8

The interaction between molecules influences the binding of another
* e.g F-2,6-P2 increases PFK-1 activity
* e.g F-2,6-P2 inhibits FBPase-1 activity

Question 9

What do hormones alter in relation to enzymes?

Answer 9

Activity of enzymes
* Rapid, via phosphorylation
* Short-lived effect

Number of enzymes
* Slow, via gene expression changes
* Longer-lived effect

Question 10

How does phosphorylation alter the activity of enzymes?

Answer 10

Phosphorylation –> Conformational change
–> Activation or Inactivation