Krebs Cycle

Definition

The Krebs Cycle, also known as the citric acid cycle or tricarboxylic acid (TCA) cycle, is a series of chemical reactions that take place in the mitochondria of cells, where acetyl-CoA is oxidized to produce energy. This cycle is crucial for cellular respiration, linking carbohydrate, fat, and protein metabolism to energy production and the generation of electron carriers for the electron transport chain.

5 Must Know Facts For Your Next Test

1. The Krebs Cycle involves eight enzymatic reactions that convert acetyl-CoA into carbon dioxide while producing energy-rich molecules like NADH and FADH2.
2. Each turn of the Krebs Cycle produces three NADH molecules, one FADH2 molecule, and one GTP (or ATP), which are crucial for energy production in the cell.
3. The cycle begins with the condensation of acetyl-CoA with oxaloacetate to form citrate, which then undergoes several transformations before regenerating oxaloacetate.
4. Regulation of the Krebs Cycle occurs through key enzymes such as citrate synthase and isocitrate dehydrogenase, responding to levels of ATP and NADH.
5. The Krebs Cycle is interconnected with other metabolic pathways, playing a vital role in biosynthesis and providing intermediates for amino acid synthesis.

Review Questions

• How does the Krebs Cycle connect different macronutrients to energy production in cells?
  • The Krebs Cycle serves as a central hub for metabolism by integrating carbohydrates, fats, and proteins into energy production. Acetyl-CoA, derived from these macronutrients, enters the cycle to be oxidized into carbon dioxide. During this process, high-energy carriers such as NADH and FADH2 are produced, which are then utilized in the electron transport chain to generate ATP. This integration allows cells to efficiently use various nutrient sources for energy.
• What role do NADH and FADH2 play after they are produced in the Krebs Cycle?
  • NADH and FADH2 are crucial electron carriers generated during the Krebs Cycle. After their production, they enter the electron transport chain located in the inner mitochondrial membrane. Here, they donate electrons to drive a series of redox reactions that ultimately lead to ATP synthesis through oxidative phosphorylation. The energy released from these electrons is used to pump protons across the membrane, creating a proton gradient that powers ATP synthase.
• Evaluate how alterations in enzyme activity within the Krebs Cycle can affect overall cellular metabolism.
  • Alterations in enzyme activity within the Krebs Cycle can significantly impact cellular metabolism by disrupting the balance of energy production and substrate availability. For instance, if citrate synthase is inhibited, acetyl-CoA cannot effectively enter the cycle, leading to reduced production of NADH and FADH2. This would lower ATP generation via oxidative phosphorylation and could lead to an accumulation of upstream metabolites. Conversely, overactive enzymes might result in excessive energy production or depletion of key intermediates needed for biosynthetic pathways, illustrating how finely tuned this cycle must be for optimal cellular function.

Related terms

Acetyl-CoA: A central metabolite in cellular respiration that enters the Krebs Cycle, formed from carbohydrates, fats, and proteins.

NADH:

A coenzyme that acts as an electron carrier in cellular respiration, generated during the Krebs Cycle and used in the electron transport chain to produce ATP.

Mitochondria: Organelles known as the powerhouses of the cell, where the Krebs Cycle and other key metabolic processes occur to generate energy.