key term - Energy payoff phase

Definition

The energy payoff phase refers to the second half of glycolysis, where ATP is generated and NADH is produced from glucose breakdown. This phase is crucial because it results in a net gain of energy, allowing cells to harness the energy stored in glucose molecules for various metabolic processes.

5 Must Know Facts For Your Next Test

1. During the energy payoff phase, four ATP molecules are produced through substrate-level phosphorylation, but only two net ATPs are gained because two ATPs are used in the earlier investment phase.
2. The production of NADH in this phase occurs when glyceraldehyde-3-phosphate (G3P) is oxidized, capturing high-energy electrons that can later be used in the electron transport chain.
3. Enzymes such as phosphoglycerate kinase and pyruvate kinase are critical during this phase, facilitating the reactions that lead to ATP generation.
4. The energy payoff phase results in the conversion of glucose into two molecules of pyruvate, which can then enter the citric acid cycle for further energy extraction.
5. This phase not only contributes to energy production but also plays a role in regulating various metabolic pathways based on cellular energy needs.

Review Questions

• How does the energy payoff phase contribute to the overall process of glycolysis?
  • The energy payoff phase is essential as it converts the products from the earlier investment phase into usable energy. During this stage, ATP is produced through substrate-level phosphorylation and NADH is generated, which can be utilized in later stages of cellular respiration. This phase effectively transforms the chemical energy stored in glucose into forms that the cell can readily use, making it a crucial step in glycolysis.
• Discuss the role of enzymes in the energy payoff phase and their impact on ATP production.
  • Enzymes like phosphoglycerate kinase and pyruvate kinase play vital roles in facilitating reactions during the energy payoff phase. These enzymes catalyze key steps that lead to substrate-level phosphorylation, which directly generates ATP. The efficiency and regulation of these enzymes impact how much ATP is produced, affecting the overall energy yield from glycolysis and ensuring that cells can adapt to their energy demands.
• Evaluate how the outcomes of the energy payoff phase can influence cellular metabolism under varying conditions.
  • The outcomes of the energy payoff phase can significantly influence cellular metabolism, particularly under anaerobic or aerobic conditions. For instance, when oxygen is scarce, pyruvate produced may enter fermentation pathways instead of aerobic respiration, impacting NADH recycling and ATP yield. Conversely, under aerobic conditions, pyruvate enters the citric acid cycle, allowing for additional ATP production and NADH utilization. Thus, the efficiency of this phase affects not just immediate energy availability but also broader metabolic pathways and adaptations to environmental changes.

Related terms

ATP:

Adenosine triphosphate (ATP) is the primary energy carrier in all living organisms, providing energy for various cellular functions.

NADH:

Nicotinamide adenine dinucleotide (NADH) is a coenzyme that plays a key role in cellular respiration, serving as an electron carrier in metabolic reactions.

substrate-level phosphorylation:

A process of generating ATP directly from the transfer of a phosphate group to ADP from another phosphorylated compound, which occurs during glycolysis.