Citric Acid Cycle

Definition

The citric acid cycle, also known as the Krebs 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, connecting glycolysis to the electron transport chain while producing key energy carriers such as NADH and FADH2.

5 Must Know Facts For Your Next Test

1. The citric acid cycle occurs in the mitochondria of eukaryotic cells and in the cytoplasm of prokaryotic cells.
2. For each turn of the cycle, three molecules of NADH, one molecule of FADH2, and one molecule of ATP (or GTP) are produced.
3. The cycle begins with the condensation of acetyl-CoA with oxaloacetate to form citric acid, which undergoes a series of transformations.
4. The citric acid cycle is also involved in biosynthetic processes, providing intermediates for amino acids and other biomolecules.
5. Regulation of the citric acid cycle occurs at key enzymatic steps, influenced by energy status and the availability of substrates.

Review Questions

• How does the citric acid cycle integrate with glycolysis and other metabolic pathways?
  • The citric acid cycle is closely connected to glycolysis through the production of acetyl-CoA from pyruvate generated during glycolysis. This connection allows for a seamless transition between the breakdown of glucose and further energy production. Additionally, intermediates from the citric acid cycle can enter various biosynthetic pathways, indicating its central role in both catabolism and anabolism within cellular metabolism.
• Discuss the significance of NADH and FADH2 production in the context of cellular respiration.
  • NADH and FADH2 are crucial energy carriers produced during the citric acid cycle. They transport high-energy electrons to the electron transport chain, where their energy is used to generate ATP through oxidative phosphorylation. The efficiency of cellular respiration largely depends on these molecules since they help convert the energy stored in nutrients into usable cellular energy, making them essential for aerobic life.
• Evaluate how regulation of the citric acid cycle affects overall cellular metabolism and energy production.
  • The regulation of the citric acid cycle plays a vital role in maintaining cellular energy balance. Key enzymes are regulated based on the cell's energy status; high levels of ATP or NADH signal that energy production can slow down, while low levels indicate a need for increased activity. This regulatory mechanism ensures that cells adapt their metabolism according to their energy demands, linking energy production with consumption effectively.

Related terms

Glycolysis: A metabolic pathway that converts glucose into pyruvate, generating a small amount of ATP and NADH in the process.

NADH: A reduced coenzyme that carries electrons to the electron transport chain, playing a vital role in ATP production during cellular respiration.

Acetyl-CoA: A key molecule that enters the citric acid cycle, formed from the breakdown of carbohydrates, fats, and proteins.