Tricarboxylic acid cycle

Definition

The tricarboxylic acid cycle, also known as the citric acid cycle or Krebs 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 cellular respiration, connecting metabolic pathways and providing electrons for oxidative phosphorylation, where ATP is produced.

5 Must Know Facts For Your Next Test

1. The tricarboxylic acid cycle occurs in the mitochondria of eukaryotic cells and in the cytoplasm of prokaryotes.
2. One complete turn of the cycle processes one acetyl-CoA molecule, resulting in the production of 3 NADH, 1 FADH2, and 1 GTP or ATP.
3. The cycle involves eight enzymatic reactions that include key steps like the conversion of citrate to isocitrate and the decarboxylation of α-ketoglutarate.
4. Regulation of the tricarboxylic acid cycle is vital for controlling energy production and is influenced by substrates, product concentrations, and energy needs of the cell.
5. Intermediates from the tricarboxylic acid cycle are also used in other metabolic pathways, such as amino acid synthesis and gluconeogenesis.

Review Questions

• How does the tricarboxylic acid cycle contribute to energy production in cells?
  • The tricarboxylic acid cycle generates high-energy electron carriers like NADH and FADH2 during its reactions. These carriers are essential because they transfer their electrons to the electron transport chain during oxidative phosphorylation. This process ultimately leads to the production of ATP, which is the primary energy currency in cells.
• Discuss how regulation of the tricarboxylic acid cycle affects overall cellular metabolism.
  • Regulation of the tricarboxylic acid cycle is crucial for maintaining metabolic balance. Key enzymes like citrate synthase and α-ketoglutarate dehydrogenase are regulated by various factors including substrate availability and energy status. When energy demand is low, intermediates may accumulate and signal a decrease in cycle activity, while high levels of NADH or ATP can inhibit these enzymes to prevent excessive energy production.
• Evaluate the role of intermediates from the tricarboxylic acid cycle in other metabolic pathways and their importance in cellular function.
  • Intermediates from the tricarboxylic acid cycle serve as critical building blocks for various biosynthetic processes. For instance, oxaloacetate can be used for gluconeogenesis, while alpha-ketoglutarate plays a role in amino acid synthesis. This versatility highlights the cycle's centrality not only in energy metabolism but also in providing necessary precursors for cellular function and growth, illustrating how interconnected metabolic pathways support overall homeostasis.

Related terms

Acetyl-CoA: A central metabolite that is derived from carbohydrates, fats, and proteins, serving as the main substrate that enters the tricarboxylic acid cycle.

Oxidative Phosphorylation: The final stage of cellular respiration where ATP is produced using the energy derived from electrons transported through the electron transport chain.

NADH: An electron carrier produced during the tricarboxylic acid cycle that donates electrons to the electron transport chain in oxidative phosphorylation.