During glycolysis, a series of enzymatic reactions take place in the cytoplasm, breaking down glucose into two molecules of pyruvic acid. This process occurs in several stages:
1. Phosphorylation: Glucose is phosphorylated twice, forming glucose-6-phosphate and fructose-1,6-bisphosphate.
2. Cleavage: Fructose-1,6-bisphosphate is cleaved into two three-carbon molecules: glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP).
3. Isomerization: DHAP is converted into GAP.
4. Oxidation: GAP is oxidized and phosphorylated to form 1,3-bisphosphoglycerate (1,3-BPG). This step involves the removal of hydrogen atoms from GAP and the transfer of these electrons to NAD+, reducing it to NADH.
5. ATP synthesis: 1,3-BPG is converted into 3-phosphoglycerate (3-PG), generating a molecule of ATP through substrate-level phosphorylation.
6. Further oxidation: 3-PG is oxidized to 2-phosphoglycerate (2-PG), and another molecule of NADH is produced.
7. Phosphoglycerate Mutase Reaction: 2-phosphoglycerate is converted to phosphoenolpyruvate (PEP).
8. Second ATP synthesis: PEP is converted into pyruvate, generating a second molecule of ATP through substrate-level phosphorylation.
9. Pyruvate Formation: The loss of a water molecule from PEP results in the formation of pyruvate. This marks the end of glycolysis.
So, glycolysis is the process that refers to the oxidation of glucose to pyruvate, yielding a net gain of 2 molecules of ATP, 2 molecules of NADH, and 2 molecules of pyruvate. These products serve as vital intermediates for further metabolic pathways, such as the citric acid cycle (Krebs cycle), where the pyruvate molecules undergo further oxidation and energy extraction to generate ATP.
