Atp

2 H2O

2 molecules of new 3-carbon compound

figure 7-3

Glycolysis takes place in the cytosol of cells and involves four main steps. A net yield of two ATP molecules is produced for every molecule of glucose that undergoes glycolysis.

In step G, the two G3P molecules are oxidized, and each receives a phosphate group. The product of this step is two molecules of a new three-carbon compound. As shown in Figure 7-3, the oxidation of G3P is accompanied by the reduction of two molecules of nicotinamide adenine dinucleotide (NAD+) to NADH. NAD+ is similar to NADP+, a compound involved in the light reactions of photosynthesis. Like NADP+, NAD+ is an organic molecule that accepts electrons during redox reactions.

In step Q, the phosphate groups added in step O and step G are removed from the three-carbon compounds formed in step G. This reaction produces two molecules of pyruvic acid. Each phosphate group is combined with a molecule of ADP to make a molecule of ATP. Because a total of four phosphate groups were added in step O and step G, four molecules of ATP are produced.

Notice that two ATP molecules were used in step O, but four were produced in step Q. Therefore, glycolysis has a net yield of two ATP molecules for every molecule of glucose that is converted into pyruvic acid. What happens to the pyruvic acid depends on the type of cell and on whether oxygen is present.

figure 7-3

Glycolysis takes place in the cytosol of cells and involves four main steps. A net yield of two ATP molecules is produced for every molecule of glucose that undergoes glycolysis.

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