Glycolysis

Glycolysis is a key chemical reaction that occurs in both aerobic and anaerobic respiration, but does not require oxygen. In this reaction, glucose is converted into two molecules of pyruvic acid and four adenosine triphosphate molecules. These ATP molecules contain energy. Since this process uses two ATPs, the cell gains a total of two ATP molecules during glycolysis. Glycolysis consists of nine steps. First, a phosphate group is added to the glucose molecule using an enzyme called hexokinase to form glucose-6-phosphate. In the second step, the enzyme phosphoglucose isomerase reorganizes the molecule and changes its structure from a six-membered ring to a five-membered ring. Next, the molecule, now fructose-6-phosphate gains another phosphate group with the help of phosphofructokinase, creating fructose- 1,6-bisphosphate. During the fourth step of glycolysis, another enzyme, aldolase, breaks the fructose- 1,6-biphosphate into two carbon-3 molecules.

In the next step of glycolysis, the carbon-3 molecules are oxidized by an NAD molecule, which takes a hydrogen atom from the carbon-3. In addition, the carbon-3 molecules receive another phosphate group with glyceraldehyde-3-phosphate dehydrogenase serving as a catalyst, resulting in 1,3 bisphoglycerate. After this the enzyme phosphoglycerate kinase is involved in a reaction in which an ADP molecule receives a phosphate group from each 1,3 bisphoglycerate molecule, forming two ATPs and two 3 phosphoglycerate molecules. An enzyme called phosphoglycerate mutase then rearranges the placement of the phosphates on the 3 phosphoglycerate to make 2 phosphoglycerate. Next, enolase takes a water molecule from the 2 phosphoglycerate and forms the product phosphoenolpyruvate. Finally, the enzyme pyruvate kinase catalyzes a reaction that moves a phosphate group from the phosphoenolpyruvate molecules to ADP molecules, creating two more ATPs and pyruvic acid, the final products of glycolysis.