In the Cori cycle, when glucose is degraded by glycolysis to lactate in muscle, the lactate is excreted into the blood and returns to the liver. In the liver, lactate is converted back into glucose by gluconeogenesis. For each given enzyme, identify whether it is involved in the glycolysis pathyway, gluconeogenesis pathway, both pathways, or neither pathway. 1. glyceraldehyde 3-phosphate dehydrogenase
a. glycolysis
b. gluconeogenesis
c. both
d. neither
2. glucose-6-phosphatase
a. glycolysis
b. gluconeogenesis
c. both
d. neither
3. alcohol dehydrogenase
a. glycolysis
b. gluconeogenesis
c. both
d. neither
4. phosphoenolpyruvate carboxykinase
a. glycolysis
b. gluconeogenesis
c. both
5. phosphofructokinase-1
a. glycolysis
b. gluconeogenesis
c. both
d. neither
6. phosphoglycerate mutase
a. glycolysis
b. gluconeogenesis
c. both
d. neither
7. hexokinase
a. glycolysis
b. gluconeogenesis
c. both
d. neither
8. pyruvate dehydrogenase
a. glycolysis
b. gluconeogenesis
c. both
d. neither

The correct answer is -

1. c. both

2. b. gluconeogenesis

3. d. neither

4. b. gluconeogenesis

5. a. glycolysis

6. c. both

7. a. glycolysis

8. d. neither

Explanation:

Gluconeogenesis is the formation or synthesis of glucose while glycolysis is the conversion of glucose into pyruvate. Gluconeogenesis requires an enzyme for a non-reversal reaction which is not required in glycolysis.

Glyceraldehyde 3-phosphate dehydrogenase is an enzyme present in glycolysis that converts glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate. It is a reversible reaction, this enzyme also present during gluconeogenesis converts 1,3-bisphosphoglycerate to glyceraldehyde 3-phosphate.

Glucose 6-phosphate to glucose during gluconeogenesis by glucose-6-phosphatase. Alcohol dehydrogenase is used for the conversion of ethanol into acetaldehyde and neither present in glyconeogenesis nor glycolysis. Oxaloacetate converts to phosphoenol pyruvate during gluconeogenesis by Phosphoenol pyruvate carboxykinase.

Fructose 6-phosphate changes into fructose 1,6-bisphosphate by Phosphofructokinase-1 during glycolysis.

Phosphoglycerate mutase is present in both pathways during glycolysis and during gluconeogenesis. This enzyme converts 3-phosphoglycerate to 2-phosphoglycerate and also converts 2-phosphoglycerate to 3-phosphoglycerate in glycolysis and gluconeogenesis respectively.

Hexokinase converts glucose to glucose 6-phosphate during glycolysis. However, Pyruvate dehydrogenase neither present in glycolysis nor gluconeogenesis.

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