LECTURE 5 - GLUCONEOGENESIS + CORI CYCLE Flashcards
a dysregulation of which enzymes would cause a fructose intolerance?
fructokinase
fructose-1-phosphate aldolase
what are all the options that G6P can become?
- can be converted back to glucose
- can be made into glycogen
- can be made into Ribose-5-phosphate through the PPP
- can be made into pyruvate to then into glycolysis
why is glutathione reductase important and what does it rely on?
is the enzyme in the salvaging reaction which converts GSSH to GSH
this enzyme depends on NADPH, which is why NADPH is needed by every cell to prevent damage by oxidation
what is gluconeogenesis?
biosynthesis of new glucose from non carbohydrate sources
when is gluconeogenesis needed?
dietary glucose is not available
exhaustion of intracellular glucose
glycogen pool in liver is depleted
blood glucose levels are about to below normal
where does gluconeogenesis occur?
in the liver (major) and in the kidney (minor)
what are the substrates of gluconeogenesis?
lactate
pyruvate
intermediates from the CAC
amino acids (muscle)
NOT from fatty acids (but their breakdown generates ATP)
what is the starting point of gluconeogenesis?
oxaloacetate (an intermediate of CAC)
what steps does gluconeogenesis share with glycolysis?
the two processes share their reversible steps
what enzymes are required by the irreversible steps of gluconeogenesis?
pyruvate carboxylase
PEPCK
FBPase
glucose-6-phosphatase
where is glucose-6-phophatase found?
in the liver only
what does gluconeogenesis consume/require?
requires NADH and requires ATP/GTP
(makes sense, its the reverse of glycolysis)
what does PEPCK stand for?
phosphoenolpyruvate carboxykinase
what are the pyruvate carboxylase and PEPCK reactions?
make phosphoenolpyruvate (PEP)
pyruvate carboxylase: carboxylation
PEPCK: decarboxylation
what do pyruvate carboxylase and PEPCK require?
pyruvate (from amino acid catabolism)
energy, ATP (from catabolism of fatty acids)
acetyl-CoA (from catabolism of fatty acids), which is an allosteric activator!!
how are the enzyme reactions of pyruvate carboxylase and PEPCK coupled?
pyruvate carboxylase uses ATP to make a high energy intermediate from pyruvate: oxaloacetate
the exergonic decarboxylation of oxaloacetate provides the energy for making PEP
when does the cori cycle happen?
happens in absence of O2 and abundance of lactate, because in anaerobic conditions glucose becomes lactate
what does the cori cycle regenerate?
regenerates NAD+ which is needed for glycolysis
where does the cori cycle happen
muscle, liver (and most cells)
what happens to pyruvate and NADH in no oxygen conditions?
pyruvate and NADH in the muscle become L-Lactate and NAD+
what then happens to the L-lactate and the NAD+?
transporters efflux L-lactate into the bloodstream, and NAD+ replenishes the NAD+ pool to continue glycolysis
so what is the cori cycle
lactate goes from the muscle to the liver, through the bloodstream
in the liver lactate is converted back into glucose, and glycolysis can continue
pathways of glucose
how would these pathways be different in the presence of oxygen?
how would these pathways be different in the absence of oxygen?
how would these pathways be different in cell division?
how would these pathways be different in low blood sugar conditions?
what is the enzyme responsible for the reversible reaction of pyruvate to lactate or vice versa?
lactate dehydrogenase
