Krebs Cycle

Definition

The Krebs Cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA. This cycle plays a central role in cellular respiration, linking the breakdown of carbohydrates, fats, and proteins to the production of ATP, NADH, and FADH2, which are vital for energy transfer and metabolic processes.

5 Must Know Facts For Your Next Test

1. The Krebs Cycle occurs in the mitochondria of eukaryotic cells and is crucial for aerobic respiration.
2. Each turn of the cycle produces three NADH molecules, one FADH2 molecule, and one GTP (or ATP) molecule, highlighting its role in energy metabolism.
3. Intermediates from the Krebs Cycle are not only used for energy production but also serve as building blocks for amino acids and other biomolecules.
4. The cycle is regulated by various enzymes and can be influenced by the availability of substrates such as acetyl-CoA and oxygen.
5. The Krebs Cycle generates carbon dioxide as a waste product, which is expelled from the cell and eventually exhaled by organisms.

Review Questions

• How does the Krebs Cycle connect the metabolism of carbohydrates, fats, and proteins to energy production?
  • The Krebs Cycle serves as a central hub for energy metabolism by accepting acetyl-CoA from the breakdown of carbohydrates, fats, and proteins. This cycle oxidizes acetyl-CoA to produce energy-rich molecules like NADH and FADH2. These products enter the electron transport chain, leading to ATP generation. Therefore, it integrates various metabolic pathways into a cohesive energy-producing process.
• Discuss how the regulation of enzymes within the Krebs Cycle impacts metabolic efficiency.
  • Enzymes within the Krebs Cycle are tightly regulated by factors such as substrate availability and product concentrations. For instance, high levels of NADH indicate sufficient energy supply, signaling a reduction in cycle activity. Conversely, an abundance of substrates like acetyl-CoA can enhance enzyme activity. This regulation ensures that energy production aligns with cellular demands, maximizing metabolic efficiency.
• Evaluate the role of anaplerotic reactions in maintaining the function of the Krebs Cycle and their significance in overall metabolism.
  • Anaplerotic reactions are essential for replenishing intermediates of the Krebs Cycle that may be siphoned off for biosynthetic pathways. Without these reactions, key intermediates would deplete over time, disrupting the cycle's function and leading to reduced ATP production. This maintenance is critical not only for sustaining energy supply but also for supporting various metabolic pathways that rely on Krebs Cycle intermediates for building blocks.

Related terms

Acetyl-CoA: A key molecule that enters the Krebs Cycle, formed from the breakdown of carbohydrates, fats, and proteins, serving as the primary fuel for energy production.

NADH:

A coenzyme that acts as an electron carrier, produced during the Krebs Cycle and utilized in the electron transport chain to generate ATP.

Anaplerotic Reactions: Reactions that replenish intermediates of the Krebs Cycle, ensuring its continuous operation and providing precursors for various biosynthetic pathways.