Citric acid cycle

Definition

The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA. It connects carbohydrate, fat, and protein metabolism to energy production by converting acetyl-CoA into carbon dioxide while producing high-energy electron carriers, NADH and FADH2, which are crucial for ATP production.

5 Must Know Facts For Your Next Test

1. The citric acid cycle takes place in the mitochondrial matrix and consists of eight main enzymatic reactions.
2. During each turn of the cycle, one acetyl-CoA molecule produces three NADH, one FADH2, and one GTP or ATP.
3. The cycle plays a critical role in the catabolism of carbohydrates, fats, and proteins, highlighting its importance in energy metabolism.
4. Regulation of the citric acid cycle occurs at several key enzymes such as citrate synthase and isocitrate dehydrogenase, which respond to levels of ATP and NADH.
5. The byproducts of the citric acid cycle include carbon dioxide, which is expelled from the body during respiration, demonstrating its role in cellular respiration.

Review Questions

• How does the citric acid cycle contribute to overall cellular respiration and energy production?
  • The citric acid cycle contributes to cellular respiration by oxidizing acetyl-CoA to produce high-energy electron carriers, NADH and FADH2. These carriers then feed into the electron transport chain during oxidative phosphorylation, where ATP is generated. By linking different metabolic pathways like carbohydrate and fat metabolism, the citric acid cycle plays a vital role in providing energy to the cell.
• Discuss how regulation of the citric acid cycle affects metabolic pathways within a cell.
  • Regulation of the citric acid cycle is essential for maintaining metabolic homeostasis within a cell. Enzymes such as citrate synthase and isocitrate dehydrogenase are regulated by energy status indicators like ATP and NADH. When energy levels are high, these regulators slow down the cycle to prevent excessive energy production. Conversely, when energy levels drop, the cycle accelerates to meet metabolic demands. This balance helps cells adapt their energy production according to current needs.
• Evaluate the implications of disruptions in the citric acid cycle on human health and disease.
  • Disruptions in the citric acid cycle can have severe implications for human health as they can lead to inadequate energy production and accumulation of toxic metabolites. For example, genetic mutations affecting enzymes in the cycle can contribute to metabolic disorders like succinate dehydrogenase deficiency or fumarate hydratase deficiency. Such conditions may lead to symptoms ranging from fatigue and muscle weakness to more severe outcomes like tumor development. Understanding these disruptions is crucial for developing targeted therapies and nutritional strategies for managing related diseases.

Related terms

NADH: A reduced form of nicotinamide adenine dinucleotide that acts as an electron carrier in the citric acid cycle, transporting electrons to the electron transport chain for ATP synthesis.

Acetyl-CoA: A key molecule in metabolism that enters the citric acid cycle, derived from carbohydrates, fats, and proteins.

Oxidative Phosphorylation: The process by which ATP is formed as a result of electrons being transferred through the electron transport chain, utilizing the high-energy carriers produced in the citric acid cycle.