The ATP produced during glycolysis is generated by a process known as substrate-level phosphorylation. This process occurs when a phosphate group is directly transferred from a substrate molecule to ADP, forming ATP.
During glycolysis, which takes place in the cytoplasm of the cell, glucose is broken down into two molecules of pyruvate. In the process, several key reactions occur where energy-rich intermediates are formed. Specifically, there are two main points in glycolysis where ATP is produced directly:
- In the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, a phosphate group is transferred to ADP, generating one ATP molecule.
- In the conversion of phosphoenolpyruvate (PEP) to pyruvate, another ATP molecule is formed in a similar manner.
Overall, glycolysis net produces two ATP molecules per glucose molecule, despite an initial investment of two ATP molecules in the early stages. The process is vital for cellular respiration, as it allows the cell to harness energy quickly, even in the absence of oxygen.