Glycolysis

Glycolysis

Glycolysis is the breakdown of hexose sugar, usually glucose, into two molecules of the 3-carbon compound pyruvate (pyruvic acid). It occurs in all cells, and in anaerobic organisms it is the only stage of respiration. Initially the glucose is insufficiently reactive and so it is phosphorylated first to split into two triose sugar molecules.

1. The glucose molecule is phosphorylated to make it more reactive. The phosphate molecule comes from the conversion of ATP to ADP.

2. The glucose molecule is reorganized into its isomer fructose phosphate.

3. The fructose phosphate is further activated by the donation of a second phosphate group by an ATP molecule to make it more reactive.

4. The 6-carbon fructose diphosphate is split into two 3-carbon triose phosphate molecules.

5. A phosphate molecule is lost and ATP is regenerated.

6. A phosphate molecule is lost and ATP is formed. A water molecule is also lost for each triose phosphate.

7. Each glucose molecule produces two molecules of glycerate 3-phosphate — a pair for every glucose molecule.

The energy yield is a net gain of two molecules of ATP.

The total yield of energy is therefore two molecules of ATP directly and six molecules of ATP produced from the two reduced NAD molecules. A total of eight ATP molecules.