Carbohydrate Energy Production 3

Question 1

What is Allostery?

Answer 1

When an activator or inhibitor binds at another site

Question 2

What is covalent modification? Give an example of this

Answer 2

• Phosphorylation or Dephosphorylation
• Alters structure and activity
• Protein Kinase transfers phosphate group from ATP to the protein

Question 3

What is the difference between Irreversible and Reversible steps in Metabolic Pathways?

Answer 3

Irreversible - Potential sites of regulation
Reversible - Not regulated
- Even when inhibited equilibrium maintains balance

Question 4

Name 3 characteristics of product inhibition of B in the reaction B C

Answer 4

• Reversible
• Reduces binding rate of B to active site
• Reduces rate of catalysis of B to C
• Inhibits pathway flow

Question 5

What is Feedback Inhibition and at which stage is it most efficient?

Answer 5

• Often Allosteric inhibition by the final product on the first enzyme
• Most efficient at the point of regulation

Question 6

What is Commiting Step inhibition?

Answer 6

Inhibition that allows substrate to be diverted and be available for other reactions

Question 7

Describe the effect of key enzyme regulation on Catabolic Pathways

Answer 7

• Catabolic pathways are inhibited by high energy signals

- Catabolic pathways are activated by low energy signals

Question 8

What can regulation of key enzymes predict?

Answer 8

Signal pathways

Question 9

Give 2 examples of high and low energy signals

Answer 9

High Energy - ATP, NADH, FAD2H

Low Energy - ADP, AMP, NAD+, FAD

Question 10

What is the effect of hormonal regulation?

Answer 10

Stimulates phosphorylation control of the target enzyme and activates the signalling pathway

Question 11

Give an example of an enzyme that phosphorylates and one that dephosphorylates

Answer 11

Phosphorylation- Protein Kinase

Dephosphorylation - Protein Phosphatase

Question 12

What does phosphorylation/dephosphorylation alter?

Answer 12

Protein conformation/activity depending on the enzyme

Question 13

What is Feed Forward Regulation?

Answer 13

When an early pathway substrate provides a positive allosteric signal stimulating a later enzyme to activate the pathway

Question 14

Give an example of a Feed Forward substrate in Glycolysis

Answer 14

Fructose 2,6 Biphosphate

Question 15

Describe the phosphoregulation of Adrenaline

Answer 15

1. Adrenaline activates PKA

2. Phosphorylation of enzymes stimulates glycogen breakdown

Question 16

Describe the phosphoregulation of Insulin

Answer 16

1. Insulin activates Protein Phosphotase

2. Glucose utilised and glycogen breakdown inhibited by dephosphorylation

Question 17

What is the key regulator of Glycolysis and what is special about this step?

Answer 17

• Phosphofructokinase-1 (PFK)

- Step 3 is the committing step of Glycolysis

Question 18

What is Metabolic Regulation? Give an example of this in Glycolysis

Answer 18

• Product inhibition of the next step due to high energy levels
• In glycolysis when there is high NADH and NAD+
• NADH stored or used in other pathways > Glycolysis Inhibited

Question 19

How can Glycolysis be Allosterically Regulated?

Answer 19

By the ATP:AMP ratio’s effect on Phosphofructokinase

Question 20

What acts as a positive allosteric regulator of Glycolysis?

Answer 20

• High levels of AMP

- Fructose 2,6 Biphosphate

Question 21

Name 3 negative allosteric regulators of Glycolysis

Answer 21

• High ATP levels
• Citrate (in Krebs cycle)
• H+ (acidity inhibits enzyme)
• PEP (substrate for last enzyme)

Question 22

How can phosphoregulation of PFK react to glucose levels?

Answer 22

High glucose > insulin > dephosphorylation of Protein Phosphotase 1 > PFK activates and uses excess glucose

Low glucose > glucagon > phosphorylation of Protein Kinase A > PFK inhibited and glucose is spared

Question 23

What other enzyme in Glycolysis can be phosphoregulated?

Answer 23

Pyruvate Kinase

Question 24

How does Glucose-6-Phosphate allosterically regulate Hexokinase?

Answer 24

• G-6-P is a negative regulator of its own enzyme
• Product inhibition of G-6-P
• Prevents inappropriate use of glucose
• Metabolic regulation