Control of Pathways Flashcards
What are instant reserves of ATP and how long can this supply energy for?
The pool of compounds able to do substrate-level phosphorylation. Only seconds of supply.
Where is the energy released from in ATP?
When any of the terminal phosphates are hydrolysed.
What is the role of adenylate kinase?
Catalyses the reaction of 2ADP together to give ATP and AMP. Holds 3 nucleotides in equilibrium. The ratio of the three gives energy charge (level of energy in the cell).
What determines whether the energy charge will be high or low?
AMP levels.
Why are ATP:ADP:AMP ratios set at the level they are at? What is this ratio?
ATP>ADP»AMP. This is because key enzymes re very sensitive to AMP, somewhat to ADP and not much to ATP, so there can be higher levels of it.
How do enzymes in a pathway regulate the flow?
The slowest enzyme in the pathway determines the overall speed - Rate-limiting step and flux generating step.
What happens to the rate of a reaction if you double or halve the concentration of substrate in a reaction when substrate concentration is high?
Nothing, at high substrate levels minor changes in the substrate will not affect the rate of reaction.
What are the properties of the rate-limiting step of a reaction?
Irreversible: Need alternative enzymes to go back Saturated with substrate: Low Km or [S]>>Km Working at Vmax.
What are the three major ways to regulate Flux?
Change the intrinsic activity of the step
Make more gates open
Make and destroy gates according to need
Where are RLS located in catabolism/ by which mechanisms do they work?
Usually in transport areas or trapping reactions (trap them in a certain place) or require substrate in short supply or switched on and off.
What is PFK?
First enzyme of glycolysis.
How is PFK involved in a rate-limiting step? Give 2 examples.
Allosterically - the molecule has bound to the enzyme at a site that changes the shape of the site and makes it behave differently. E.g binds AMP and changes way PFK responds to ATP and binds to citrate which inhibits itself (PFK).
What is hexokinase and how does it work as an RLS?
Initial glucose trapping reaction. Inhibition by its product, G6P, which prevents excessive trapping. Prevents the waste of ATP and allows glucose to go back out of the cell.
What happens to glucose if G6P is not being used?
It is not trapped in the cell.
What pathways allow glycolysis to speed up during exercise?
Release of high energy charge inhibition, the release of negative feedback etc.. stops inhibition/ reduces RLS.
