Citric Acid Cycle

Definition

The citric acid cycle, also known as the Krebs cycle or tricarboxylic acid (TCA) cycle, is a key metabolic pathway that takes place in the mitochondria of cells. It is crucial for the aerobic respiration process, where acetyl-CoA is oxidized to produce energy in the form of ATP, as well as NADH and FADH2, which are vital for further energy production in the electron transport chain. This cycle plays a significant role in nutrient metabolism, contributing to the overall energy balance and cellular functions.

5 Must Know Facts For Your Next Test

1. The citric acid cycle consists of a series of eight enzymatic reactions that regenerate oxaloacetate, allowing the cycle to continue processing acetyl-CoA.
2. In addition to producing energy, the citric acid cycle provides precursors for various biosynthetic pathways, supporting the synthesis of amino acids and fatty acids.
3. For each turn of the citric acid cycle, three molecules of NADH, one molecule of FADH2, and one molecule of ATP (or GTP) are produced.
4. The cycle is regulated by key enzymes, which can be influenced by the availability of substrates and energy needs of the cell, ensuring efficient energy production.
5. In conditions of low oxygen availability (hypoxia), cells may switch to anaerobic metabolism, reducing reliance on the citric acid cycle for energy production.

Review Questions

• How does the citric acid cycle contribute to energy production in cells?
  • The citric acid cycle contributes to energy production by oxidizing acetyl-CoA to produce high-energy molecules such as NADH and FADH2. These molecules then enter the electron transport chain, where their energy is harnessed to generate ATP through oxidative phosphorylation. This process is crucial for meeting the energy demands of cells during aerobic respiration.
• Discuss how the citric acid cycle is integrated with other metabolic pathways in nutrient metabolism.
  • The citric acid cycle is integrated with several metabolic pathways, including carbohydrate metabolism, fatty acid oxidation, and amino acid catabolism. Intermediates from these pathways can be converted into acetyl-CoA or other substrates that enter the cycle. Additionally, products generated from the citric acid cycle serve as precursors for biosynthetic processes like gluconeogenesis and fatty acid synthesis, illustrating its central role in maintaining metabolic balance.
• Evaluate the impact of impaired citric acid cycle function on overall metabolism and health.
  • Impaired function of the citric acid cycle can lead to significant disruptions in overall metabolism and health. Reduced energy production due to diminished ATP synthesis can result in fatigue and decreased cellular function. Furthermore, accumulation of intermediates may indicate metabolic blockages, which can contribute to various health issues such as diabetes and neurodegenerative diseases. Understanding these implications highlights the importance of maintaining proper functioning of this metabolic pathway for overall health.

Related terms

Acetyl-CoA: A central metabolite that enters the citric acid cycle, derived from carbohydrates, fats, and proteins during their breakdown.

Electron Transport Chain: A series of protein complexes located in the inner mitochondrial membrane that utilizes NADH and FADH2 from the citric acid cycle to generate ATP through oxidative phosphorylation.

ATP: A high-energy molecule that serves as the primary energy currency of the cell, produced during cellular respiration processes including the citric acid cycle.