Glycolysis

Glycolysis, or the Embden-Meyerhof pathway, is the first step in glucose catabolism and is universal across most organisms.

This pathway consists of two stages. In the preparatory stage, glucose is phosphorylated using one ATP molecule to form glucose-6-phosphate.

This intermediate is then isomerized into fructose-6-phosphate, which undergoes phosphorylation using another ATP to produce fructose-1,6-bisphosphate.

Finally, fructose-1,6-bisphosphate is split into two three-carbon intermediates: glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, which isomerize to yield two identical molecules of glyceraldehyde-3-phosphate.

In the energy-conserving stage, each glyceraldehyde-3-phosphate molecule is oxidized to pyruvate, producing 2 NADH and 4 ATP molecules via substrate-level phosphorylation.

The net energy yield of glycolysis is two ATP molecules and two NADH molecules per molecule of glucose.

The final product of glycolysis is two molecules of pyruvate, which can enter aerobic or anaerobic pathways depending on cellular conditions.