Citric acid cycle

Definition

The citric acid cycle, also known as the Krebs cycle or TCA cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. This cycle plays a central role in cellular respiration, linking carbohydrate metabolism to the production of ATP and the regulation of electron transport and oxidative phosphorylation.

5 Must Know Facts For Your Next Test

1. The citric acid cycle occurs in the mitochondrial matrix and consists of eight enzyme-catalyzed reactions that convert acetyl-CoA into carbon dioxide and high-energy electron carriers.
2. Each turn of the cycle generates three molecules of NADH, one molecule of FADH2, and one molecule of GTP or ATP, which are crucial for energy production.
3. Regulation of the citric acid cycle is influenced by substrate availability and feedback mechanisms involving ATP, ADP, and NADH levels.
4. The cycle not only contributes to ATP production but also provides intermediates for various biosynthetic pathways, integrating metabolism across different macromolecules.
5. Disruptions in the citric acid cycle can lead to metabolic disorders and are associated with various diseases, highlighting its importance in maintaining cellular energy homeostasis.

Review Questions

• How does the citric acid cycle integrate carbohydrate metabolism with energy production?
  • The citric acid cycle integrates carbohydrate metabolism by utilizing acetyl-CoA, which is derived from glucose breakdown during glycolysis. As glucose is converted into pyruvate, it is further processed to form acetyl-CoA before entering the cycle. The cycle then generates high-energy electron carriers like NADH and FADH2 that are crucial for driving ATP synthesis through oxidative phosphorylation, effectively linking carbohydrate metabolism to energy production.
• Discuss how the regulation of the citric acid cycle influences overall cellular respiration and energy homeostasis.
  • Regulation of the citric acid cycle is critical for maintaining energy homeostasis within the cell. The levels of substrates such as acetyl-CoA and products like NADH serve as signals for regulating enzymatic activity in the cycle. For instance, high NADH levels can inhibit certain enzymes in the cycle, reducing its activity when energy supply exceeds demand. This regulation helps coordinate the flow of metabolites through cellular respiration, ensuring efficient energy production while preventing excess energy accumulation.
• Evaluate the consequences of impaired function in the citric acid cycle on cellular metabolism and health.
  • Impaired function in the citric acid cycle can significantly disrupt cellular metabolism and lead to a range of health issues. If the cycle is not functioning properly, it can result in decreased ATP production and accumulation of metabolic intermediates. This imbalance may contribute to metabolic disorders, as cells struggle to generate sufficient energy or utilize substrates effectively. Additionally, disruptions can lead to increased oxidative stress due to unregulated electron transport chain activity, further exacerbating health problems such as neurodegeneration or cardiovascular diseases.

Related terms

Acetyl-CoA: A key molecule that enters the citric acid cycle, formed from the breakdown of carbohydrates, fats, and proteins.

NADH:

A high-energy electron carrier produced during the citric acid cycle that donates electrons to the electron transport chain.

Oxidative Phosphorylation: The process in which ATP is produced using energy derived from the electron transport chain, heavily reliant on the products of the citric acid cycle.