Question

Gluconeogenesis is generally the reverse of the glycolytic pathway, producing glucose from pyruvate. Some tissues cannot survive without a source of glucose, and this is a way to produce glucose from other food molecules.

(A) 7 reactions in glycolysis are used in the reverse direction in gluconeogenesis. How can this be?

Answer 1

Glycolysis is composed of 10 reactions out of which 7 reaction steps in reverse direction occurs in gluconeogenesis but three steps of glycolysis cannot be reversed. The 7 reactions of glycolysis is reversible and thus they can alternate between products and reactants. But three steps of glycolysis is irreversible. .These three reaction are occur by different enzymes in gluconeogenesis.

1. Glucose is converted to glucose 6-phosphate by the enzyme Hexokinase in glycolysis

  Glucose 6 phosphate is converted to glucose by the enzyme Glucose 6-phosphatase in gluconeogenesis.

2. Fructose 6 phosphate is converted to Fructose 1-6 bisphosphate by the enzyme phsphofructokinase in glycolysis.

Fructose 1-6 bisphosphate is converted to Fructose 6 phosphate by the enzyme Fructose 1-6 bisphosphatase in gluconeogenesis

3. Phosphoenol pyruvate is converted to pyruvate by the enzyme Pyruvate kinase in glycolysis

Pyruvate is converted to Phosphoenol pyruvate through oxaloacetate intermediate by two enzymes pyruvate carboxylase and Phosphoenolpyruvate carboxykinase. in gluconeogenesis.

All the other 7 reactions of gluconeogenesis is mediated by the same enzyme used in glycolysis but in reverse direction.