LECTURE 3 - CARBOHYDRATES Flashcards
how is PFK1 allosterically modulated?
AMP is an allosteric activator
ATP is an allosteric inhibitor
F2,6P is an allosteric activator
transition from the T state (ATP bound) to the R state (AMP bound) activates PFK1
how are PFK and FBPase in a substrate cycle at rest?
how are PFK and FBPase in a substrate cycle during exercise?
what reaction does PFK2/FBPase catalyse?
F6P–> F2,6P
FBPase does the reverse (removes a phosphate)
what is the function of F2,6P?
NOT an intermediate in glycolysis
a strong modulator of PFK1 (activates)
compare PFK1 and PFK2 in these characteristics:
how does the enzyme work
catalysed reaction
role in glycolysis
activity
modulators
what is the hormonal regulation of PFK2 in the liver isozyme?
happens during fast or prolonged exercise
blood glucose level is low
glucagon increases, goes to the liver, which increases cAMP, which activates PKA, which phosphorylates PFK2, and that inhibits PFK2
the kinase activity is lower than the phosphatase activity, which means that there is less F2,6P, this shuts off PFK1
you get gluconeogenesis
what is the hormonal regulation of PFK2 in the heart muscle isozyme?
this works opposite to the liver isozyme
happens during stress
epinephrine increases, binds to receptors on heart muscle surface, which increases cAMP, which increases PKA, which phosphorylates PFK2, but this will increase its activity
more phosphatase than kinase, more F2,6P, which means more PFK1 so you get glycolysis
what does aldolase do?
splits on 6 carbon sugar in two 3 carbon intermediates
this reaction is close to equilibrium
makes GAP and DHAP at equal concentrations from FBP
what does triose phosphate isomerase do?
converts GAP and DHAP one from the other
GAP is now the substrate for glycolysis
in cells, there is more DHAP than GAP because GAP is being siphoned off to be used in glycolysis
TIM converts DHAP to GAP to maintain equilibrium
how many GAP are generated per glucose?
2
what are the GAPDH and phosphoglycerate kinase reactions?
GAP is turned by GAPDH into a high energy intermediate which is rapidly converted to 3PG by phosphoglycerate kinase
the two reactions are thermodynamically coupled
the high energy intermediate has a very short life span, passed between the two enzymes which are close to each other, doesn’t accumulate
what does the GAPDH and phosphoglycerate kinase reactions produce per glucose?
2 NADH and 2 ATP
what does mutase do?
transfers phosphate from position 3 to position 2
what does enolase do?
dehydrates 2-phosphoglycerate to phosphoenolpyruvate (PEP)
PEP is a high energy intermediate
