Citric Acid Cycle

Definition

The citric acid cycle, also known as the Krebs cycle or tricarboxylic acid (TCA) cycle, is a key metabolic pathway that takes place in the mitochondria of cells. It plays a crucial role in cellular respiration by converting acetyl-CoA into carbon dioxide and transferring high-energy electrons to electron carriers, ultimately contributing to the production of ATP. This cycle not only generates energy but also provides precursors for various primary and secondary metabolites essential for cellular functions.

5 Must Know Facts For Your Next Test

1. The citric acid cycle consists of eight main steps, beginning with the condensation of acetyl-CoA and oxaloacetate to form citrate.
2. For each turn of the cycle, three molecules of NADH, one molecule of FADH2, and one molecule of GTP (or ATP) are produced.
3. The cycle also produces carbon dioxide as a waste product, which is expelled from the body during respiration.
4. Intermediates from the citric acid cycle can serve as building blocks for the synthesis of amino acids, nucleotides, and other essential biomolecules.
5. The regulation of the citric acid cycle is influenced by the availability of substrates like acetyl-CoA and the energy needs of the cell, ensuring efficient metabolic responses.

Review Questions

• How does the citric acid cycle contribute to cellular metabolism beyond energy production?
  • The citric acid cycle not only plays a crucial role in energy production through ATP generation but also serves as a hub for biosynthetic processes. The intermediates produced during the cycle can be utilized to synthesize important biomolecules such as amino acids and nucleotides. This dual role makes the citric acid cycle essential for maintaining cellular function and supporting growth and repair.
• Discuss the importance of NADH produced in the citric acid cycle in relation to oxidative phosphorylation.
  • NADH generated during the citric acid cycle is critical for oxidative phosphorylation, as it donates electrons to the electron transport chain located in the inner mitochondrial membrane. This transfer of electrons leads to the establishment of a proton gradient across the membrane, which is then utilized by ATP synthase to produce ATP. Therefore, NADH serves as a key link between the metabolic pathways of cellular respiration and energy production.
• Evaluate how anaplerotic reactions support the continuous function of the citric acid cycle and its connection to primary and secondary metabolites.
  • Anaplerotic reactions play a vital role in replenishing intermediates within the citric acid cycle that may be siphoned off for biosynthesis of primary and secondary metabolites. By ensuring that essential substrates are available for continuous operation of the cycle, these reactions allow cells to maintain metabolic balance while also producing necessary compounds for growth and stress response. This connection underscores how metabolic pathways are interlinked, influencing overall cellular health and adaptability.

Related terms

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

NADH: An electron carrier produced during the citric acid cycle, which is vital for the electron transport chain and ATP synthesis.

Anaplerotic Reactions: Reactions that replenish intermediates in the citric acid cycle, ensuring its continuous operation and support for biosynthesis.