Outcomes of Glycolysis


OpenStax Biology 2e

Glycolysis begins with glucose and produces two pyruvate molecules, four new ATP molecules, and two molecules of NADH. (Note: two ATP molecules are used in the first half of the pathway to prepare the six-carbon ring for cleavage, so the cell has a net gain of two ATP molecules and two NADH molecules for its use). If the cell cannot catabolize the pyruvate molecules further, it will harvest only two ATP molecules from one molecule of glucose. Mature mammalian red blood cells do not have mitochondria and thus are not capable of aerobic respiration—the process in which organisms convert energy in the presence of oxygen—and glycolysis is their sole source of ATP. If glycolysis is interrupted, these cells lose their ability to maintain their sodium-potassium pumps, and eventually, they die.

– Where does glycolysis mostly occur?

The last step in glycolysis will not occur if pyruvate kinase, the enzyme that catalyzes the formation of pyruvate, is not available in sufficient quantities. In this situation, the entire glycolysis pathway will proceed, but only two ATP molecules will be made in the second half. Thus, pyruvate kinase is a rate-limiting enzyme for glycolysis.

Many enzymes are involved in the glycolytic pathway by converting one intermediate to another. Control of these enzymes, such as hexokinase, phosphofructokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase can regulate glycolysis by. The amount of oxygen available can also regulate glycolysis. The “Pasteur Effect” describes how the availability of oxygen diminishes the effect of glycolysis, and decreased availability leads to an acceleration of glycolysis, at least initially. The mechanisms responsible for this effect include the involvement of allosteric regulators of glycolysis (enzymes such as hexokinase). The “Pasteur Effect” appears to mostly occur in tissue with high mitochondrial capacities, such as myocytes or hepatocytes, but this effect is not universal in oxidative tissue, such as pancreatic cells.


Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/biology-2e



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