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 derived from carbohydrates, fats, and proteins. This cycle plays a crucial role in cellular respiration, linking glycolysis to oxidative phosphorylation and producing key energy carriers like NADH and FADH2.

5 Must Know Facts For Your Next Test

1. The Krebs cycle takes place in the mitochondria of eukaryotic cells and in the cytoplasm of prokaryotic cells.
2. For each acetyl-CoA molecule that enters the Krebs cycle, two carbon dioxide molecules are released, and three NADH and one FADH2 molecules are produced.
3. The cycle is named after Hans Krebs, who first elucidated its steps in 1937, earning him the Nobel Prize in Physiology or Medicine in 1953.
4. The Krebs cycle involves eight distinct steps that regenerate oxaloacetate, allowing the cycle to continue processing additional acetyl-CoA molecules.
5. Regulatory enzymes in the Krebs cycle help control its activity based on cellular energy needs, influenced by levels of ATP, ADP, NAD+, and other metabolites.

Review Questions

• How does the Krebs cycle contribute to energy production in aerobic organisms?
  • The Krebs cycle contributes to energy production by oxidizing acetyl-CoA into carbon dioxide while generating high-energy electron carriers like NADH and FADH2. These carriers play a crucial role in transporting electrons to the electron transport chain during oxidative phosphorylation. This process ultimately leads to the production of ATP, which is the primary energy currency of the cell, ensuring that aerobic organisms can efficiently utilize energy from various macronutrients.
• Discuss how the regulation of key enzymes in the Krebs cycle influences cellular respiration.
  • The regulation of key enzymes such as citrate synthase and isocitrate dehydrogenase is essential for controlling the flow of substrates through the Krebs cycle. These enzymes respond to changes in the levels of ATP, ADP, NAD+, and other metabolites to either stimulate or inhibit the cycle's activity. This regulation ensures that the Krebs cycle operates efficiently based on cellular energy demands, helping maintain metabolic homeostasis within the cell.
• Evaluate the interconnectedness of glycolysis, the Krebs cycle, and oxidative phosphorylation in cellular respiration.
  • Glycolysis converts glucose into pyruvate, which is then transformed into acetyl-CoA for entry into the Krebs cycle. The Krebs cycle processes acetyl-CoA to produce NADH and FADH2 while releasing carbon dioxide. These electron carriers are then utilized in oxidative phosphorylation to generate ATP. This interconnected pathway highlights how each stage relies on products from previous reactions to maximize energy extraction from nutrients, demonstrating a well-coordinated system vital for cell survival and function.

Related terms

Acetyl-CoA:

A central metabolite that is derived from carbohydrates, fats, and proteins, serving as the main substrate for the Krebs cycle.

NADH:

An electron carrier produced during the Krebs cycle that transports electrons to the electron transport chain for ATP production.

Oxidative phosphorylation: The process by which ATP is produced using the energy released from the electron transport chain, which follows the Krebs cycle.