What is glycolysis? What are its steps?

SouravAugust 18, 2024

Answer

Glycolysis is a fundamental metabolic pathway that breaks down glucose (a six-carbon sugar) into two molecules of pyruvate (a three-carbon compound) while producing ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide). It occurs in the cytoplasm of cells and is the first step in both aerobic and anaerobic respiration.

Here’s a summary of the steps involved in glycolysis:

1. Phosphorylation of Glucose: Glucose is phosphorylated to form glucose-6-phosphate (G6P). This step is catalyzed by the enzyme hexokinase (or glucokinase in the liver) and uses one molecule of ATP.
2. Isomerization of G6P: Glucose-6-phosphate is converted to fructose-6-phosphate (F6P) by the enzyme phosphoglucose isomerase.
3. Second Phosphorylation: Fructose-6-phosphate is phosphorylated to form fructose-1,6-bisphosphate (F1,6BP). This step is catalyzed by phosphofructokinase-1 (PFK-1) and also uses one molecule of ATP.
4. Cleavage of F1,6BP: Fructose-1,6-bisphosphate is split into two three-carbon molecules: dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P). This step is catalyzed by aldolase.
5. Isomerization of DHAP: Dihydroxyacetone phosphate is converted to glyceraldehyde-3-phosphate, so there are now two molecules of G3P.
6. Oxidation and Phosphorylation: Each G3P is oxidized to 1,3-bisphosphoglycerate (1,3-BPG) by the enzyme glyceraldehyde-3-phosphate dehydrogenase, producing one NADH per molecule of G3P.
7. First ATP Formation: 1,3-Bisphosphoglycerate is converted to 3-phosphoglycerate (3-PG) with the production of one ATP per molecule of 1,3-BPG. This step is catalyzed by phosphoglycerate kinase.
8. Conversion of 3-PG to 2-PG: 3-Phosphoglycerate is converted to 2-phosphoglycerate (2-PG) by the enzyme phosphoglycerate mutase.
9. Dehydration of 2-PG: 2-Phosphoglycerate is dehydrated to form phosphoenolpyruvate (PEP) by the enzyme enolase.
10. Second ATP Formation and Pyruvate Production: Phosphoenolpyruvate is converted to pyruvate with the production of one ATP per molecule of PEP. This step is catalyzed by pyruvate kinase.