key term - Citric acid cycle

Definition

The citric acid cycle, also known as the Krebs cycle or 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. It plays a crucial role in cellular respiration, linking the breakdown of glucose in glycolysis and pyruvate oxidation to the production of ATP through oxidative phosphorylation in the electron transport chain.

5 Must Know Facts For Your Next Test

1. The citric acid cycle occurs in the mitochondrial matrix and is a cyclic series of reactions that regenerate oxaloacetate to continue the cycle.
2. Each turn of the citric acid cycle produces three NADH molecules, one FADH2 molecule, and one GTP or ATP molecule, which are used in oxidative phosphorylation to produce more ATP.
3. The cycle also releases two molecules of carbon dioxide for each acetyl-CoA that enters, contributing to cellular respiration's overall process of converting glucose to energy.
4. Key enzymes in the cycle include citrate synthase, aconitase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase, each facilitating specific reactions.
5. The citric acid cycle not only plays a role in energy production but also provides intermediates for various biosynthetic pathways, linking metabolism with other cellular functions.

Review Questions

• How does the citric acid cycle connect glycolysis and pyruvate oxidation to the production of ATP?
  • The citric acid cycle acts as a crucial link between glycolysis and pyruvate oxidation by processing acetyl-CoA, which is derived from pyruvate after it enters the mitochondria. During each turn of the cycle, acetyl-CoA is oxidized to produce energy-rich molecules like NADH and FADH2. These carriers then feed into oxidative phosphorylation where their stored energy is used to generate ATP, thus effectively connecting carbohydrate metabolism with energy production.
• Analyze the role of NADH produced in the citric acid cycle and its importance for ATP generation during oxidative phosphorylation.
  • NADH produced in the citric acid cycle serves as a critical electron carrier that transports electrons to the electron transport chain during oxidative phosphorylation. As NADH donates electrons to this chain, it helps create a proton gradient across the inner mitochondrial membrane. This gradient drives ATP synthase to convert ADP and inorganic phosphate into ATP. Without NADH from the citric acid cycle, there would be insufficient electron flow to produce significant amounts of ATP.
• Evaluate how intermediates from the citric acid cycle contribute to other metabolic pathways beyond energy production.
  • Intermediates generated during the citric acid cycle serve essential roles in various biosynthetic pathways. For example, α-ketoglutarate can be converted into amino acids like glutamate, while citrate can be transported out of the mitochondria to form fatty acids. This versatility highlights how the citric acid cycle not only functions in energy production but also supports cellular growth and maintenance by providing precursors for macromolecule synthesis.

Related terms

Acetyl-CoA:

A key molecule that enters the citric acid cycle, formed from the breakdown of carbohydrates, fats, and proteins, serving as the starting point for energy production.

Oxidative Phosphorylation: The process that occurs in the mitochondria where ATP is produced using the energy released by electrons as they are transferred through the electron transport chain.

NADH:

A coenzyme that acts as an electron carrier in cellular respiration, produced during glycolysis, pyruvate oxidation, and the citric acid cycle, crucial for ATP generation.