Carbohydrate Energy Production 3 Flashcards
What is Allostery?
When an activator or inhibitor binds at another site
What is covalent modification? Give an example of this
- Phosphorylation or Dephosphorylation
- Alters structure and activity
- Protein Kinase transfers phosphate group from ATP to the protein
What is the difference between Irreversible and Reversible steps in Metabolic Pathways?
Irreversible - Potential sites of regulation
Reversible - Not regulated
- Even when inhibited equilibrium maintains balance
Name 3 characteristics of product inhibition of B in the reaction B C
- Reversible
- Reduces binding rate of B to active site
- Reduces rate of catalysis of B to C
- Inhibits pathway flow
What is Feedback Inhibition and at which stage is it most efficient?
- Often Allosteric inhibition by the final product on the first enzyme
- Most efficient at the point of regulation
What is Commiting Step inhibition?
Inhibition that allows substrate to be diverted and be available for other reactions
Describe the effect of key enzyme regulation on Catabolic Pathways
- Catabolic pathways are inhibited by high energy signals
- Catabolic pathways are activated by low energy signals
What can regulation of key enzymes predict?
Signal pathways
Give 2 examples of high and low energy signals
High Energy - ATP, NADH, FAD2H
Low Energy - ADP, AMP, NAD+, FAD
What is the effect of hormonal regulation?
Stimulates phosphorylation control of the target enzyme and activates the signalling pathway
Give an example of an enzyme that phosphorylates and one that dephosphorylates
Phosphorylation- Protein Kinase
Dephosphorylation - Protein Phosphatase
What does phosphorylation/dephosphorylation alter?
Protein conformation/activity depending on the enzyme
What is Feed Forward Regulation?
When an early pathway substrate provides a positive allosteric signal stimulating a later enzyme to activate the pathway
Give an example of a Feed Forward substrate in Glycolysis
Fructose 2,6 Biphosphate
Describe the phosphoregulation of Adrenaline
- Adrenaline activates PKA
2. Phosphorylation of enzymes stimulates glycogen breakdown
Describe the phosphoregulation of Insulin
- Insulin activates Protein Phosphotase
2. Glucose utilised and glycogen breakdown inhibited by dephosphorylation
What is the key regulator of Glycolysis and what is special about this step?
- Phosphofructokinase-1 (PFK)
- Step 3 is the committing step of Glycolysis
What is Metabolic Regulation? Give an example of this in Glycolysis
- 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
How can Glycolysis be Allosterically Regulated?
By the ATP:AMP ratio’s effect on Phosphofructokinase
What acts as a positive allosteric regulator of Glycolysis?
- High levels of AMP
- Fructose 2,6 Biphosphate
Name 3 negative allosteric regulators of Glycolysis
- High ATP levels
- Citrate (in Krebs cycle)
- H+ (acidity inhibits enzyme)
- PEP (substrate for last enzyme)
How can phosphoregulation of PFK react to glucose levels?
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
What other enzyme in Glycolysis can be phosphoregulated?
Pyruvate Kinase
How does Glucose-6-Phosphate allosterically regulate Hexokinase?
- G-6-P is a negative regulator of its own enzyme
- Product inhibition of G-6-P
- Prevents inappropriate use of glucose
- Metabolic regulation
