Citrate

Definition

Citrate is a key intermediate in the citric acid cycle, also known as the Krebs cycle, which is a central metabolic pathway in cellular respiration. It is the conjugate base of citric acid and plays a crucial role in energy production within the mitochondria of cells.

5 Must Know Facts For Your Next Test

1. Citrate is the conjugate base of citric acid, a six-carbon tricarboxylic acid that is a key intermediate in the citric acid cycle.
2. The citric acid cycle is a central metabolic pathway in cellular respiration, where it oxidizes acetyl-CoA to carbon dioxide while generating ATP and reducing coenzymes.
3. Citrate synthase is the enzyme that catalyzes the first reaction of the citric acid cycle, condensing acetyl-CoA and oxaloacetate to form citrate.
4. The citric acid cycle is a cyclic pathway, with citrate as the first and last intermediate, and it occurs in the mitochondria of cells.
5. Citrate is also involved in the regulation of cellular metabolism, as it can inhibit the activity of phosphofructokinase, a key enzyme in glycolysis.

Review Questions

• Explain the role of citrate in the citric acid cycle and its importance in cellular respiration.
  • Citrate is a key intermediate in the citric acid cycle, also known as the Krebs cycle, which is a central metabolic pathway in cellular respiration. The citric acid cycle is a series of chemical reactions that occur in the mitochondria of cells, converting acetyl-CoA derived from the breakdown of carbohydrates, fats, and proteins into carbon dioxide, while generating ATP and reducing coenzymes for the electron transport chain. Citrate synthase, the enzyme that catalyzes the first reaction of the citric acid cycle, condenses acetyl-CoA and oxaloacetate to form citrate, which then enters the cycle. The cyclic nature of the citric acid cycle, with citrate as the first and last intermediate, is essential for the continuous oxidation of acetyl-CoA and the efficient production of energy in the form of ATP.
• Describe the relationship between citrate and the regulation of cellular metabolism.
  • In addition to its role in the citric acid cycle, citrate is also involved in the regulation of cellular metabolism. Citrate can act as an allosteric inhibitor of the enzyme phosphofructokinase, which is a key enzyme in the glycolytic pathway. When citrate levels are high, it inhibits phosphofructokinase, slowing down glycolysis and directing the metabolism of glucose towards the citric acid cycle instead. This regulatory mechanism helps to maintain the balance between glycolysis and the citric acid cycle, ensuring that the cell's energy production is optimized. By inhibiting phosphofructokinase, citrate can also influence the partitioning of metabolic substrates, such as directing glucose towards fatty acid synthesis or other anabolic pathways, depending on the cell's energy needs and the availability of nutrients.
• Analyze the role of citrate synthase in the citric acid cycle and explain how its activity is regulated to control the overall rate of the cycle.
  • Citrate synthase is the enzyme that catalyzes the first and rate-limiting step of the citric acid cycle, condensing acetyl-CoA and oxaloacetate to form citrate. As the gatekeeper of the cycle, the activity of citrate synthase is tightly regulated to control the overall rate of the citric acid cycle and, consequently, the cell's energy production. Citrate synthase can be allosterically inhibited by high levels of ATP, NADH, and succinyl-CoA, which are all products or intermediates of the citric acid cycle. This feedback inhibition helps to prevent the cycle from running too quickly and depleting the cell's energy stores. Conversely, citrate synthase can be allosterically activated by ADP and AMP, which signal a need for increased energy production. Additionally, the expression and activity of citrate synthase can be modulated by hormonal and nutritional signals, allowing the cell to adjust its energy metabolism in response to changing environmental and physiological conditions. By tightly regulating the activity of citrate synthase, the cell can fine-tune the rate of the citric acid cycle to match its energy demands.

Related terms

Citric Acid Cycle:

The citric acid cycle, or Krebs cycle, is a series of chemical reactions that occur in the mitochondria of cells, converting acetyl-CoA derived from the breakdown of carbohydrates, fats, and proteins into carbon dioxide, while generating ATP and reducing coenzymes for the electron transport chain.

Citrate Synthase:

Citrate synthase is the enzyme that catalyzes the first reaction of the citric acid cycle, condensing acetyl-CoA and oxaloacetate to form citrate, the six-carbon tricarboxylic acid that enters the cycle.

Acetyl-CoA:

Acetyl-CoA is a key molecule in cellular metabolism, serving as the entry point for the citric acid cycle. It is produced from the breakdown of carbohydrates, fats, and proteins and provides the two-carbon acetyl group that combines with oxaloacetate to form citrate.