Energy Production In Carbohydrates 3 Flashcards
What is allostery?
Activator/inhibitor binds at another site on enzyme
Metabolic pathway regulation
Irreversible steps can cause regulation
Reducing level of products, less substrate can get through pathways
Flux through pathways is regulated in response to need
Why are reversible steps not regulated?
Even when inhibited, reactions still come to an equilibrium so levels of product are unaffected
How does product inhibition work?
As pathway intermediates build so flux pathway will slow
Can block first enzyme in pathway, reduces entry of substrate and build up of intermediates in pathway - feedback inhibition
What does inhibiting the committing step do?
Allows substrate to be diverted into other pathways
Regulation of key enzymes
Can be inhibitory or stimulatory
E.g. catabolic pathways inhibited by high energy signals, activated by low energy signals
How does hormonal regulation work?
Hormone receptor binding
Activates signalling pathway
Protein kinase or protein phosphatase activated
Dephosphorylation/phosphorylation of target enzyme
Alters protein conformation/activity positively or negatively depending on target enzyme
What is feeding forward?
Early pathway substrate provides positive allosteric signal to stimulate a later enzyme to activate pathway
An example of phosphoregulation - adrenaline
Activates protein kinase A
Phosphorylation activates phosphorylase kinase
Phosphorylation of glycogen phosphorylase - stimulates glycogen breakdown
An example of phosphoregulation - insulin
Activates phosphatase 1
Dephosphorylaes/activates pyruvate dehydrogenase - stimulates glucose utilisation
Dephosphorylates glycogen phosphorylase
How does phosphofructokinase-1 regulate glycolysis?
Fructose-6-phosphate -> fructose-1,6-bisphosphate using phosphofructokinase-1, converting ATP to ADP
Allosteric regulation of phsophofructokinase-1 by ATP:AMP ratio
Allosteric regulation in muscle
Inhibited at high ATP
Stimulated at high AMP
Hormonal regulation in liver
Stimulated by insulin using protein phosphatase 1
Inhibited by glucagon using protein kinase A
What happens if there is a high NADH concentration in step 6 of glycolysis?
High energy levels
Causes product inhibition
Inhibition of glycolysis
Allosteric regulation of hexokinase by glucose-6-phosphate
Inhibition at step 6, high NADH=high energy level
Inhibition at step 4, PFK in response to high energy signals
Prevents metabolism of F1, 6-BP, backs up glycolytic intermediates, increased G-6-P
G-6-P negative regulator of hexokinase
