Question

What is the purpose of each step in glycolysis? (This does not mean what are the products formed in each step, although it is for a select few). Which steps are key steps? Why?

Answer 1

Glycolysis is a series of biochemical reactions that derive energy from glucose by splitting it into two three-carbon molecules called pyruvate. Glycolysis has 10 steps (when the starting molecule is Glucose 6 phosphate) which are classified into two phases:

1. Preperatory /energy requiring phase

2. Pay off/Energy releasing phase.

> In the preperatory phase, Glucose 6 phosphate a six carbon compound, is converted to its isomer Fructose-6-phosphate and then phosphorylated to Fructose 1,6 bisphosphate, a relatively less stable compound and is cleaved enzymatically by aldolase to Glyceraldehyde-3 phosphate / GAP (a 3 carbon compound) and Dihyroxyacetone phosphate/ DHAP (another 3 carbon compound).

The purpose of these steps is to convert the Glucose 6 phosphate molecule to its isomer Fructose-6-phosphate , prime the Fructose 6 phosphate molecule with phosphate so that two high energy 3C molecule can be derived from it.

DHAP may go to other anabolic cycles or may be isomerised to GAP and continue in the glycolytic cycle.

>In pay off phase the GAP(3C) is dephosphorylated to release energy as atp and NADH2 molecule and gets converted to Pyruvate(3C).

The key regulatory steps of glycolysis are the reactions catalyzed by hexokinase, phosphofructokinase, and pyruvate kinase as they are virtually irreversible so these enzymes are expected to have regulatory and catalytic roles.