Introduction
During glycolysis each molecule of glucose is converted into two molecules of pyruvate, a net gain of two ATP, and two NADH, while releasing energy that powers cellular processes. This ten‑step pathway, occurring in the cytoplasm of most cells, breaks down a six‑carbon sugar into two three‑carbon compounds, extracting chemical energy and preparing the cell for subsequent aerobic or anaerobic metabolism.
Steps
The glycolytic pathway can be divided into three phases, each containing specific reactions that are catalyzed by distinct enzymes. Below is a concise list of the ten reactions, presented in the order they occur:
- Glucose phosphorylation – Hexokinase (or glucokinase in the liver) transfers a phosphate from ATP to glucose, forming glucose‑6‑phosphate.
- Isomerization – Phosphoglucose isomerase converts glucose‑6‑phosphate into fructose‑6‑phosphate, enabling the next phosphorylation.
- Second phosphorylation – Phosphofructokinase‑1 (PFK‑1) adds another phosphate from ATP to fructose‑6‑phosphate, producing fructose‑1,6‑bisphosphate.
- Cleavage – Aldolase splits fructose‑1,6‑bisphosphate into two three‑carbon sugars: dihydroxyacetone phosphate (DHAP) and glyceraldehyde‑3‑phosphate (G3P).
- Isomerization of DHAP – Triose phosphate isomerase interconverts DHAP and G3P, ensuring that all carbon atoms enter the next steps as G3P.
- Oxidation and phosphorylation – Glyceraldehyde‑3‑phosphate dehydrogenase catalyzes the oxidation of G3P, reducing NAD⁺ to NADH and attaching inorganic phosphate to form 1,3‑bisphosphoglycerate.
- First substrate‑level phosphorylation – Phosphoglycerate kinase transfers a phosphate from 1,3‑bisphosphoglycerate to ADP, generating ATP and producing 3‑phosphoglycerate.
- Second substrate‑level phosphorylation – Phosphoglycerate mutase rearranges 3‑phosphoglycerate into 2‑phosphoglycerate, which is then converted to phosphoenolpyruvate (PEP) by enolase, releasing water.
- Final phosphorylation – Pyruvate
