Question

1. Briefly explain the regulation of gluconeogenesis and glycolysis by fructose 2,6-bisphosphate (F-2,6-BP) and how its concentration ismediated by insulin and glucagon.

Answer 1

Enzymes that catalyse metabolic pathways are potential sites for the regulatory control.

The most reactions of glycolysis are reversible but three are exergonic and are physically

irreversible.

Glucose – 6-phosphate is not solely a reaction intermediate. Glucose-6-phosphate can be

converted into glycogen or it can be oxidosed by the pentose phosphate to form NADPH.

The first irreversible reaction unique to the glycolytic pathway is the phosphorylation of

fructose-6-phosphate to fructose-1,6-bisphosphate. Hence phosphofructokinase could be

the primary control site in glycolysis.

In liver what happens is that the fructose-6-phosphate concentration rises when the blood

glucose concentration is high, and the abundance of the fructose-6-phosphate initiates the

synthesis of the F-2,6-BP. Hence the high fructose -6-phosphate leads to the higher

concentration of F-2,6-BP and in turn initiates the phosphofructokinase.