gluconeigensis

Question 1

what two steps are undertaken to bypass irreversible pyruvate kinase

Answer 1

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).

Question 2

what reaction occurs to bypass phosphofructokinase

Answer 2

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)

Question 3

what reaction occurs to bypass the hexokinase reaction

Answer 3

once glucose-6P is formed, it can be converted to glucose by the enzyme glucose-6-phosphatase - occuring in the endoplasmic reticulum

Question 4

step 1

Answer 4

• pyruvate enter the mitochondrion where it is carbodylated to oxaloacetate
• essential enzyme: Pyruvate carboxylase
• requires 1 ATP

Question 5

step 2

Answer 5

• 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

Question 6

step 3

Answer 6

• oxaloacetate is decarboxlylated andphosphorylated to phosphoenolpyruvate
• essential enzyme: phosphoenolpyruvate carboxykinase
• requires 1 GTP

Question 7

step 4

Answer 7

• phosphoenolpyruvate is converted to 2 phosphoglycerate direct reversal of glycolysis
• uses enolase

Question 8

step 5

Answer 8

• the phosphate group is transferred to a different carbon
• 2- phosphoglycerate is converted to 3- phosphoglycerate
• Direct reversal of glycolysis
• Uses enzyme phosphoglyceromutase

Question 9

step 6

Answer 9

• 3- phosphglycerate is phosphorylated to 1,3-biphosphoglycerate
• Direct reversal of glycolysis
• Requires 1 ATP
• Phosphoglycerate kinase

Question 10

step 7

Answer 10

• 1, 3-biphosphoglycerate is reduced and dephophorylated to glyceraldehyde-3-phosphate
• Direct reversal of glycolysis
• Requires 1NADH
• Glyceraldehyde-3-phosphate dehydrogenase

Question 11

step 8

Answer 11

• Next step requires both glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
• So G3P is isomerised to DHAP
• Direct reversal of glycolysis
• Triose phosphate isomerase

Question 12

step 9

Answer 12

• 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

Question 13

step 10

Answer 13

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

Question 14

step 11

Answer 14

fructose-6-phosphate is isomerised to glucose6-phosphate
* Direct reversal of glycolysis
- Phosphoglucoisomerase

Question 15

step 12

Answer 15

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