Glycolysis is the splitting or lysis of glucose. It is a multi-step reaction requiring ATP for the first steps but producing a net gain of two ATP molecules for each glucose molecule entering it. Glucose takes place in the cytoplasm of a cell.

1. During phosphorylation, glucose is phosphorylated using two ATP molecules first to hexose phosphate and then to hexose bisphosphate.

2. The hexose bisphosphate is broken down (lysis) to two molecules of triose phosphate.

3. Hydrogen is then removed from the triose phosphate and transferred to the carrier molecule NAD (nicotinamide adenine dinucleotide) and the reduced NAD (NADH2) is used during oxidative phosphorylation.

4. The oxidised triose phosphate is converted to pyruvate releasing two ATP per molecule.