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 takes place in the mitochondria of cells and plays a crucial role in cellular respiration by producing energy-rich molecules such as ATP, NADH, and FADH2, which are essential for various metabolic processes.

5 Must Know Facts For Your Next Test

1. The Krebs Cycle consists of eight main steps, each catalyzed by a specific enzyme, starting with the condensation of acetyl-CoA with oxaloacetate to form citric acid.
2. During each turn of the Krebs Cycle, two carbon atoms are released as CO2, and three molecules of NADH and one molecule of FADH2 are produced.
3. The cycle regenerates oxaloacetate at the end of each turn, allowing it to continue processing additional acetyl-CoA molecules.
4. The energy carriers produced in the Krebs Cycle (NADH and FADH2) are essential for driving the electron transport chain, leading to the majority of ATP production in aerobic respiration.
5. The Krebs Cycle is also an important metabolic hub that provides intermediates for the synthesis of various biomolecules including amino acids and nucleotides.

Review Questions

• How does acetyl-CoA enter the Krebs Cycle and what is its significance?
  • Acetyl-CoA enters the Krebs Cycle by combining with oxaloacetate to form citric acid. This step is significant because acetyl-CoA acts as a central molecule in metabolism, deriving from carbohydrates, fats, and proteins. Its entry into the Krebs Cycle initiates a series of reactions that ultimately lead to energy production. By participating in this cycle, acetyl-CoA facilitates not just energy generation but also integrates various metabolic pathways.
• Discuss the role of NADH and FADH2 produced in the Krebs Cycle in cellular respiration.
  • NADH and FADH2 produced during the Krebs Cycle play a critical role in cellular respiration by acting as electron carriers that feed into the electron transport chain. NADH carries high-energy electrons generated during the cycle, while FADH2 also contributes electrons but at a different entry point in the chain. The oxidation of these carriers leads to a proton gradient across the mitochondrial membrane, ultimately resulting in ATP synthesis through oxidative phosphorylation. Therefore, these molecules are essential for maximizing energy extraction from nutrients.
• Evaluate how the Krebs Cycle connects with glycolysis and other metabolic pathways within plant cells.
  • The Krebs Cycle serves as a vital link between glycolysis and other metabolic pathways within plant cells. Glycolysis converts glucose into pyruvate, which is then transformed into acetyl-CoA before entering the Krebs Cycle. Furthermore, intermediates from the Krebs Cycle can be utilized for synthesizing amino acids or other biomolecules, demonstrating its central role in metabolism. This connectivity ensures efficient energy production while also allowing for flexibility in resource allocation depending on cellular needs, showcasing how plants adapt their metabolic processes based on varying conditions.

Related terms

Acetyl-CoA:

A key molecule that enters the Krebs Cycle, derived from the breakdown of carbohydrates, fats, and proteins, serving as the starting point for energy production.

NADH:

A coenzyme that carries electrons and protons during cellular respiration, generated in both glycolysis and the Krebs Cycle, which is used in the electron transport chain to produce ATP.

Mitochondria: Organelles often referred to as the powerhouse of the cell, where the Krebs Cycle and other key processes of cellular respiration occur.