Glycolysis Process Overview

Glycolysis is a process that occurs in the cytoplasm of cells and involves the breakdown of one molecule of glucose into two molecules of pyruvate. This process is anaerobic, meaning it does not require oxygen, and is the first stage of cellular respiration. Glycolysis consists of two main phases: an investment phase and a payoff phase. The investment phase involves the oxidation of glucose to form two molecules of fructose-1,6-bisphosphate, which requires the consumption of two ATP molecules. The payoff phase involves the conversion of fructose-1,6-bisphosphate to two molecules of pyruvate, which releases two ATP molecules.

The steps of glycolysis include the following:

1. Glucose phosphorylation: Glucose is phosphorylated by hexokinase, forming glucose-6-phosphate. This step requires one molecule of ATP.
2. Hexose monophosphate isomerization: Glucose-6-phosphate is isomerized by phosphoglucose isomerase to form fructose-6-phosphate.
3. Phosphofructokinase: Fructose-6-phosphate is phosphorylated by phosphofructokinase to form fructose-1,6-bisphosphate. This step requires one molecule of ATP.
4. Aldolase: Fructose-1,6-bisphosphate is split into two separate sugar molecules, dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, by aldolase.
5. Triosephosphate isomerization: The molecule of dihydroxyacetone phosphate is isomerized by triosephosphate isomerase to form a second glyceraldehyde-3-phosphate.
6. Phosphoglycerate kinase: Glyceraldehyde-3-phosphate is phosphorylated by glyceraldehyde-3-phosphate dehydrogenase to form 1,3-bisphosphoglycerate. This step requires NAD+ as a cofactor.
7. Phosphoglycerate mutase: 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate by phosphoglycerate kinase. This step involves the transfer of a phosphate molecule to ADP to form 1 molecule of ATP.
8. Phosphoglycerate mutase: 3-phosphoglycerate rearranges to form 2-phosphoglycerate by the enzyme phosphoglycerate mutase.
9. Enolase: 2-phosphoglycerate is dehydrated to produce phosphoenolpyruvate by the enzyme enolase.
10. Pyruvate kinase: Phosphoenolpyruvate is converted to pyruvate by pyruvate kinase. This step involves the transfer of a phosphate molecule to ADP to form 1 molecule of ATP.

In addition to the steps above, glycolysis also involves the production of two NADH molecules, which can be used in subsequent metabolic pathways. The pyruvate molecules produced can enter the citric acid cycle or be used as a precursor for other reactions.

Glycolysis is regulated by the availability of glucose, as well as by the enzymes involved in the pathway. The breakdown of glycogen, a storage form of glucose, can also regulate glycolysis. The amount of oxygen available can also regulate glycolysis, with increased oxygen availability decreasing the rate of glycolysis.