key term - Energy payoff phase

Definition

The energy payoff phase refers to the second half of glycolysis, where energy is generated in the form of ATP and NADH through substrate-level phosphorylation. During this phase, the six-carbon glucose molecule that was broken down earlier produces two three-carbon molecules called pyruvate, and energy-carrying molecules are produced, which are critical for cellular respiration and energy metabolism.

5 Must Know Facts For Your Next Test

1. During the energy payoff phase, a total of four ATP molecules are generated through substrate-level phosphorylation, although two are used in the earlier investment phase, resulting in a net gain of two ATP.
2. NADH is produced when NAD+ is reduced during the conversion of glyceraldehyde-3-phosphate (G3P) to 1,3-bisphosphoglycerate.
3. The energy payoff phase occurs in the cytoplasm of the cell, making it anaerobic and accessible to all organisms.
4. Each molecule of glucose results in the production of two pyruvate molecules at the end of glycolysis, which can then enter either aerobic respiration or fermentation pathways.
5. This phase is essential for the overall efficiency of glucose metabolism, as it provides crucial energy carriers (ATP and NADH) that support various cellular processes.

Review Questions

• How does the energy payoff phase of glycolysis contribute to the overall efficiency of energy production in cellular respiration?
  • The energy payoff phase is crucial because it generates ATP and NADH, which are essential for powering various cellular processes. By converting one molecule of glucose into two molecules of pyruvate, this phase not only releases energy but also sets the stage for further energy extraction through aerobic respiration or fermentation. The net gain of two ATP and two NADH from glycolysis enhances the cell's ability to produce more ATP later in cellular respiration.
• Analyze how substrate-level phosphorylation during the energy payoff phase differs from oxidative phosphorylation in terms of ATP production.
  • Substrate-level phosphorylation generates ATP directly through specific enzymatic reactions involving phosphorylated intermediates during glycolysis and the citric acid cycle. In contrast, oxidative phosphorylation occurs later in cellular respiration via the electron transport chain, relying on a proton gradient to produce ATP. While substrate-level phosphorylation is simpler and occurs in anaerobic conditions, oxidative phosphorylation is more efficient and generates a larger amount of ATP when oxygen is present.
• Evaluate the importance of NADH produced during the energy payoff phase in relation to both anaerobic and aerobic metabolism.
  • NADH produced during the energy payoff phase serves as a critical electron carrier in both anaerobic and aerobic pathways. In aerobic metabolism, NADH enters the electron transport chain where it contributes to additional ATP production through oxidative phosphorylation. In anaerobic conditions, such as fermentation, NADH helps regenerate NAD+ so that glycolysis can continue without oxygen. This versatility ensures that cells can adapt their metabolic pathways based on available resources and environmental conditions.

Related terms

Glycolysis:

A metabolic pathway that converts glucose into pyruvate, producing a net gain of ATP and NADH.

Substrate-level phosphorylation: A process of generating ATP directly from a reaction involving a phosphorylated intermediate, rather than through an electron transport chain.

Pyruvate: The three-carbon compound produced at the end of glycolysis, which can be further processed in aerobic or anaerobic respiration.