Citric acid cycle

Definition

The citric acid cycle, also known as the Krebs cycle or tricarboxylic acid (TCA) cycle, is a crucial metabolic pathway that takes place in the mitochondria of cells, where it plays a central role in converting carbohydrates, fats, and proteins into energy. This cycle involves a series of enzymatic reactions that oxidize acetyl-CoA to produce ATP, NADH, and FADH2, which are essential for cellular respiration and energy production. It connects various metabolic processes and is tightly regulated to maintain cellular homeostasis.

5 Must Know Facts For Your Next Test

1. The citric acid cycle consists of eight enzymatic steps that convert acetyl-CoA into carbon dioxide while generating high-energy electron carriers (NADH and FADH2).
2. For each turn of the citric acid cycle, three molecules of NADH, one molecule of FADH2, and one molecule of GTP or ATP are produced.
3. The cycle is regulated at several key enzymes such as citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase to respond to the energy needs of the cell.
4. The citric acid cycle serves as a hub for catabolic and anabolic pathways by providing intermediates that can be used for synthesizing amino acids, nucleotides, and other biomolecules.
5. In aerobic conditions, the NADH and FADH2 produced in the citric acid cycle are utilized in oxidative phosphorylation to generate a significant amount of ATP.

Review Questions

• How does the citric acid cycle contribute to glucose metabolism?
  • The citric acid cycle is integral to glucose metabolism as it processes acetyl-CoA derived from glycolysis, where glucose is broken down. This connection ensures that the energy from glucose is efficiently converted into usable forms like ATP. Additionally, it generates high-energy electron carriers such as NADH and FADH2 that feed into the electron transport chain for further ATP production.
• Discuss how the regulation of the citric acid cycle is crucial for maintaining metabolic balance within cells.
  • Regulation of the citric acid cycle is vital for maintaining metabolic balance because it ensures that energy production matches cellular demand. Enzymes like citrate synthase and isocitrate dehydrogenase are regulated by the availability of substrates and products such as NAD+, ATP, and ADP. This regulatory mechanism allows cells to adapt to varying energy requirements and shifts between catabolic and anabolic pathways.
• Evaluate the impact of impaired function in the citric acid cycle on overall cellular metabolism and health.
  • Impaired function in the citric acid cycle can lead to decreased ATP production and accumulation of intermediates that may disrupt normal cellular functions. For instance, decreased NADH and FADH2 generation can hinder oxidative phosphorylation, resulting in energy deficits. This dysfunction can contribute to metabolic disorders and conditions such as obesity or diabetes, emphasizing the cycle's essential role in overall cellular health.

Related terms

Acetyl-CoA: A key molecule that enters the citric acid cycle, derived from carbohydrates, fats, and proteins, and serves as a substrate for energy production.

NADH: An electron carrier produced during the citric acid cycle that plays a vital role in the electron transport chain, ultimately contributing to ATP production.

Oxidative phosphorylation: The process that follows the citric acid cycle, where energy stored in NADH and FADH2 is used to generate ATP through the electron transport chain.