Citric acid cycle

Definition

The citric acid cycle, also known as the Krebs cycle or TCA cycle, is a series of chemical reactions that plays a central role in cellular respiration, where acetyl-CoA is oxidized to produce energy in the form of ATP. This cycle not only serves as a key pathway for carbohydrate metabolism but also connects lipid and amino acid metabolism, demonstrating its importance in the energy production processes of living organisms.

5 Must Know Facts For Your Next Test

1. The citric acid cycle occurs in the mitochondria of eukaryotic cells and is crucial for aerobic respiration.
2. For each turn of the cycle, one acetyl-CoA molecule yields three NADH, one FADH2, and one GTP or ATP.
3. The cycle also produces carbon dioxide as a waste product, which is expelled from the body through respiration.
4. The intermediates generated in the citric acid cycle serve as precursors for various biosynthetic pathways, including amino acid synthesis and fatty acid metabolism.
5. The regulation of the citric acid cycle is tightly controlled by substrate availability and feedback inhibition to match the energy needs of the cell.

Review Questions

• How does the citric acid cycle contribute to both carbohydrate and lipid metabolism?
  • The citric acid cycle integrates both carbohydrate and lipid metabolism by utilizing acetyl-CoA derived from glucose breakdown and fatty acid oxidation. This process allows for efficient energy production from various macromolecules. Carbohydrates are converted into glucose which enters glycolysis, producing pyruvate that forms acetyl-CoA, while lipids are broken down into fatty acids that also produce acetyl-CoA. Both pathways funnel into the citric acid cycle for ATP production.
• Discuss the significance of NADH and FADH2 produced during the citric acid cycle in cellular respiration.
  • NADH and FADH2 produced during the citric acid cycle are crucial for cellular respiration because they serve as electron carriers that transfer electrons to the electron transport chain. This transfer drives the production of ATP through oxidative phosphorylation. Each molecule of NADH contributes to approximately 2.5 ATPs, while each FADH2 contributes about 1.5 ATPs. Therefore, the efficiency of ATP generation during cellular respiration heavily relies on the availability of these coenzymes.
• Evaluate how disturbances in the citric acid cycle can affect overall metabolic processes in an organism.
  • Disturbances in the citric acid cycle can significantly disrupt metabolic processes by leading to a decrease in ATP production and an accumulation of metabolic intermediates. For instance, if a key enzyme is inhibited or dysfunctional, it could result in reduced energy output from carbohydrates, lipids, and amino acids. This not only impacts energy availability but can also lead to imbalances in biosynthetic pathways due to altered levels of metabolites used for synthesizing amino acids or fatty acids. Such imbalances can manifest in various metabolic disorders and affect overall organism health.

Related terms

Acetyl-CoA: A molecule that acts as a key fuel for the citric acid cycle, derived from carbohydrates, fats, and proteins.

NADH: A coenzyme that carries electrons to the electron transport chain, produced during the citric acid cycle and essential for ATP production.

Anaplerotic reactions: Reactions that replenish the intermediates of the citric acid cycle, ensuring its continuous function and efficiency in metabolism.