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Glycolytic Enzymes |
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INTRODUCTIONGlycolysis is an almost universal pathway for extraction of the energy available from carbohydrates, shared among prokaryotes and eukaryotes, aerobes and anaerobes alike. In anaerobes, glycolysis is the only significant source of energy from carbohydrates. In aerobic organisms, considerably more energy can be harvested downstream from glycolysis in the citric acid cycle. Glycolysis produces energy in the form of ATP and NADH. The glycolytic pathway consists of 10 enzyme-catalyzed steps. During glycolysis, glucose, a six-carbon carbohydrate, is oxidized to form two molecules of pyruvate, a three-carbon molecule. For each glucose molecule metabolized, the pathway produces two molecules of ATP and two molecules of NADH. Glycolysis is not isolated from other metabolic pathways. Other molecules besides glucose can enter at a few points along the glycolytic pathway. For example, the product of glycogen breakdown, glucose-6-phosphate, can enter the glycolytic pathway at the second step. Glyceraldehyde-3-phosphate, which is produced by photosynthesis, is also a glycolytic intermediate, so it can be directed from this anabolic pathway into glycolysis when energy is needed. Additionally, intermediates can be drawn out of the glycolytic pathway when energy levels are high, for use in biosynthetic pathways. For instance, during active energy production pyruvate, the product of glycolysis, enters the citric acid cycle, but when energy is not needed pyruvate serves as a substrate in amino acid synthesis.
Shown here is a diagram of the glycolytic pathway that includes the names of the intermediates as well as the enzymes that catalyze their modification. We will look at each of these in turn. Clicking on the name of the enzyme will take you directly to the page explaining that enzyme. Learning objectives
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