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 crucial role in metabolic networks by connecting various biochemical pathways and facilitating the production of energy-rich molecules like ATP, NADH, and FADH2 that are essential for cellular functions.

5 Must Know Facts For Your Next Test

1. The citric acid cycle occurs in the mitochondrial matrix of eukaryotic cells and is crucial for aerobic respiration.
2. For each acetyl-CoA molecule that enters the cycle, two carbon dioxide molecules are released, and high-energy electron carriers NADH and FADH2 are produced.
3. The citric acid cycle consists of eight key enzymatic reactions that regenerate oxaloacetate, allowing the cycle to continue processing new acetyl-CoA molecules.
4. The cycle is interconnected with various metabolic pathways, including glycolysis and fatty acid oxidation, highlighting its role in energy metabolism.
5. Regulation of the citric acid cycle is influenced by the availability of substrates and energy demands of the cell, with key enzymes being activated or inhibited accordingly.

Review Questions

• How does the citric acid cycle integrate with other metabolic pathways in energy production?
  • The citric acid cycle integrates with several metabolic pathways by utilizing acetyl-CoA from glycolysis and fatty acid oxidation as its primary substrate. It produces NADH and FADH2, which are crucial for oxidative phosphorylation, where more ATP is generated. Additionally, intermediates from the cycle can serve as precursors for various biosynthetic pathways, showcasing how interconnected and essential this cycle is for overall cellular metabolism.
• Evaluate the importance of NADH and FADH2 generated in the citric acid cycle in the context of cellular respiration.
  • NADH and FADH2 produced during the citric acid cycle are vital for cellular respiration as they act as electron carriers that donate electrons to the electron transport chain. This transfer of electrons leads to a series of redox reactions that create a proton gradient across the mitochondrial membrane, ultimately resulting in ATP synthesis through oxidative phosphorylation. The generation of these electron carriers represents a key step in converting metabolic energy into a usable form for cellular processes.
• Analyze how disturbances in the citric acid cycle could affect overall cellular metabolism and health.
  • Disturbances in the citric acid cycle can have significant implications for cellular metabolism and health due to its central role in energy production. If enzymes within the cycle are inhibited or dysfunctional, it can lead to reduced production of ATP, NADH, and FADH2. This can cause a cascade of metabolic disorders as cells struggle to meet their energy demands. For example, conditions like diabetes or certain mitochondrial diseases may arise when this cycle is impaired, leading to fatigue and other health issues due to insufficient energy supply.

Related terms

Acetyl-CoA: A central metabolic intermediate that enters the citric acid cycle, produced from the breakdown of carbohydrates, fats, and proteins.

NADH: A reduced coenzyme produced during the citric acid cycle that acts as an electron carrier in cellular respiration.

Oxidative Phosphorylation: The process following the citric acid cycle where ATP is produced through the electron transport chain using electrons carried by NADH and FADH2.