what two steps are undertaken to bypass irreversible pyruvate kinase
Pyruvate is carboxylated to oxaloacetate via pyruvate carboxylase; in mitochondria
The 1st step requires 1 molecule of ATP.
Pyruvate carboxylase is stimulated by high amounts of acetyl-CoA and inhibited by ADP and glucose
.
Oxaloacetate is decarboxylated and phosphorylated to phosphoenolpyruvate via
phosphoenolpyruvate carboxykinase (PEPCK).
PEPCK requires 1 molecule of guanosine triphosphate (GTP).
what reaction occurs to bypass phosphofructokinase
fructose-1,6- bisphosphate is hydrolyzed to fructose-6-phosphate by the enzyme fructose-1,6-bisphosphatase (FBPase) as follows:
Fructose-1-6-bisphophate + H2O -> Fructose-6-phosphate + Pi
(cytoplasm)
what reaction occurs to bypass the hexokinase reaction
once glucose-6P is formed, it can be converted to glucose by the enzyme glucose-6-phosphatase - occuring in the endoplasmic reticulum
step 1
- pyruvate enter the mitochondrion where it is carbodylated to oxaloacetate
- essential enzyme: Pyruvate carboxylase
- requires 1 ATP
step 2
- oxaloacetate cannot leave the mitochondrion
- it is reduced to malate
- malate moved back to the cytoplasm and is not then oxidized back to oxaloacetate
- requires 1 NADH which regenerates
step 3
- oxaloacetate is decarboxlylated andphosphorylated to phosphoenolpyruvate
- essential enzyme: phosphoenolpyruvate carboxykinase
- requires 1 GTP
step 4
- phosphoenolpyruvate is converted to 2 phosphoglycerate direct reversal of glycolysis
- uses enolase
step 5
- the phosphate group is transferred to a different carbon
- 2- phosphoglycerate is converted to 3- phosphoglycerate
- Direct reversal of glycolysis
- Uses enzyme phosphoglyceromutase
step 6
- 3- phosphglycerate is phosphorylated to 1,3-biphosphoglycerate
- Direct reversal of glycolysis
- Requires 1 ATP
- Phosphoglycerate kinase
step 7
- 1, 3-biphosphoglycerate is reduced and dephophorylated to glyceraldehyde-3-phosphate
- Direct reversal of glycolysis
- Requires 1NADH
- Glyceraldehyde-3-phosphate dehydrogenase
step 8
- Next step requires both glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
- So G3P is isomerised to DHAP
- Direct reversal of glycolysis
- Triose phosphate isomerase
step 9
- glyceraldehyde-3-phosphate and dihydroxyacetone phosphate are combined to form fructose-1,6-bisphosphate
- Direct reversal of glycolysis
- aldolase
*steps 1-8 have to be done twice to generate 2x 3C molecules to generate 1 x 6C molecules at step 9
step 10
Fructose-1,6-bisphosphate is dephosphorylated to fructose-6-phosphate
* Essential enzyme: fructose-1,6-bisphophatase
* As it does not directly reverse glycolysis, ATP is not generated at this step
step 11
fructose-6-phosphate is isomerised to glucose6-phosphate
* Direct reversal of glycolysis
- Phosphoglucoisomerase
step 12
Glucose-6-phosphate is dephosphorylated to
glucose
* Essential enzyme: glucose-6-phosphatase
* As it does not directly reverse glycolysis, ATP is
not generated at this step
