Module 3- gluconeogensis shares some reactions with glycolysis Flashcards
in glycogenesis how is the irriverible reaction of pyruvate to phosphoenolpyruvate possible
this process starts in the mitochondria with the carboxylation of pyruvate to form 4 carbon molecule called oxaloacetate
what is the reaction to get pyruvate to oxaloacetate
pyruvate+CO2+ATP+H2O<–pyruvate carboxylase–>oxaloacetate+ADP+Pi+2H+
what things does the enzyme pyruvate carboxylase require
-a covalently bound prothetic group called biotin (VB7 derivative) that carries the CO2 in a manner that facilitates its reactivity with pyruvate
-acetyl CoA which is bound to the enzyme in order to catalyze carboxylation with out it this step wouldnt occur
why is acetyl CoA called the obligate allostatic activator
acetyl CoA is bound to pyruvate carboxylase in order to catalyze carboxylation
with out it carboxylation wouldnt occur
what happens after oxaloacetate has been formed
-it needs to be transported into the cystosol in order for it to be converted to phoshoenolpyruvate
-there is no transporter for oxaloacetate so its stuck in the mitochondria
how does oxaloacetate get out of the mitochondria
-oxaloacetate is converted to malate (by malate dehydrogenase) which can leave the mitochondria
-once in the cytosol malate is converted back to oxaloacetate by the same enzyme
what happens after the oxaloacetate is in the cytosol
the final step of pyruvate to phosphoenolpyruvate can occur since the enzyme that catalyzes this (phosphoenolpyruvate carboxykinase) is found in this cellular compartment
what is the reaction from oxaloacetate to phosphoenolpyruvate
oxaloacetate+GTP<–phosphoenolpyruvate carboxykinase–>phosphoenolpyruvate+GDP+CO2
what happens once phosphoenolpyruvate is formed
its metabolized by the enzymes of glycolysis to fructose 1,6-bisP. this is possible because the reactions are all closed to eq at intracellular conditons and therefore reversible
how do we get form fructose 1,6 phosphate to fructose 6-phosphate if the reaction going the other way in glycolysis is irreversible
-it needs a different mechanism
-the enzyme used is fructose 1,6-bisphosphate, a hydrolase which cleaves off the P group using water from carbon 1 on fructose
how is fructose 6-phosphate turned into glucose 6-phosphate
it is very easily converted since the reaction catalyzed by phosphoglucose isomerase (seen in glycolysis is reversible
how does the last step of gluceogenesis work to make free glucose
-form glucose 6-P free glucose is then produced by the hydrolytic removal of the phosphate group by glucose 6-phosphatase
-the enzyme resides in the lumen (inside) of the ER
-requiring the glu 6-P produced in cytosol be shuttled into the ER
-products, Pi and glucose, are transported back to cytosol
-allowing glucose to be transp out of cell into blood
what is the overall stoichiometry of gluconeogenesis
2pyruvate+4ATP+2GTP+2NADH+2H+6H2O—>glucose+4ADP+2GDP+6Pi+2NAD+
-delta G=-38 kj
is the synthesis of glucose form pyruvate fav or unfav?
it is unfavourable except for the fact that it is coupled with reactions that release energy, such as hydrolysis of ATP and GTP
