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6.23: Glycolysis

If a person is in a catabolic state or in need of energy, such as during fasting, most glucose-6-phosphate will be used for glycolysis.

Figure 6.231 The "fork in the road" for glucose-6-phosphate

Glycolysis is the breaking down of one glucose molecule (6 carbons) into two pyruvate molecules (3 carbons). During the process, a net of two ATPs and two NADHs are also produced.

Figure 6.232 Glycolysis1

The following animation, using ball-and-stick models, allows you to control the 3 steps of glycolysis.

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Glycolysis Animation

3 steps of Glycolysis

1. Energy investment step - 2 ATP are added to the 6 carbon molecule.

Figure 6.233 Glycolysis step 1, energy investment1

2. Glucose Split - The 6 carbon molecule is split into two 3 carbon molecules.

Figure 6.234 Glycolysis step 2, glucose split1

3. Energy harvesting step - 1 NADH and 2 ATPs are produced from each 3 carbon molecule (there are two 3 carbon molecules formed from each glucose).

Figure 6.235 Glycolysis step 3, energy harvesting1

Thus, from a molecule of glucose, the harvesting step produces a total of four ATPs and two NADHs. Subtracting the harvesting from the investment step, the net output from one molecule of glucose is two ATPs and two NADHs.

The figure below shows the stages of glycolysis, as well as the transition reaction, citric acid cycle, and electron transport chain that are utilized by cells to produce energy. They are also the focus of the next 3 sections.

Figure 6.236 Glycolysis, transition reaction, citric acid cycle, and the electron transport chain2