Citrate synthase

Definition

Citrate synthase is a key enzyme in the citric acid cycle that catalyzes the condensation of acetyl-CoA and oxaloacetate to form citrate. This reaction represents the first step in the cycle and is crucial for energy production, as it marks the beginning of the process that generates ATP through the oxidation of acetyl-CoA.

5 Must Know Facts For Your Next Test

1. Citrate synthase is an allosteric enzyme, meaning its activity can be regulated by various metabolites to ensure proper functioning of the citric acid cycle.
2. The enzyme catalyzes a highly exergonic reaction, which helps drive the subsequent reactions of the citric acid cycle forward.
3. Citrate synthase is sensitive to feedback inhibition, particularly by ATP and NADH, indicating that when energy levels are high, the cycle slows down.
4. The reaction catalyzed by citrate synthase is irreversible under physiological conditions, which helps to regulate the flow of carbon into the cycle.
5. Defects in citrate synthase have been linked to certain metabolic disorders and can affect overall energy production in cells.

Review Questions

• How does citrate synthase function within the citric acid cycle and what role does it play in energy metabolism?
  • Citrate synthase catalyzes the first step of the citric acid cycle by combining acetyl-CoA with oxaloacetate to form citrate. This reaction is crucial because it initiates the series of transformations that lead to ATP generation. The production of citrate marks the entry point for carbon into the cycle, and thus, plays a central role in cellular respiration and energy metabolism.
• What are the regulatory mechanisms that influence citrate synthase activity and how do they affect the citric acid cycle?
  • Citrate synthase activity is regulated by various factors such as substrate availability, feedback inhibition from products like ATP and NADH, and allosteric modulators. When energy levels in the cell are high, elevated concentrations of ATP and NADH inhibit citrate synthase, thereby slowing down the citric acid cycle. This regulation ensures that energy production aligns with cellular needs, preventing unnecessary energy expenditure.
• Evaluate the significance of citrate synthase in relation to metabolic disorders and how its dysfunction can impact cellular energy homeostasis.
  • Citrate synthase is essential for proper functioning of the citric acid cycle; thus, its dysfunction can lead to impaired energy production and contribute to metabolic disorders. When citrate synthase is defective, it may disrupt normal flux through the cycle, leading to an accumulation of substrates or intermediates. This can result in reduced ATP synthesis and may contribute to conditions such as obesity or diabetes due to altered energy homeostasis and inefficient metabolic pathways.

Related terms

Acetyl-CoA: A molecule derived from carbohydrates, fats, and proteins that enters the citric acid cycle and serves as the starting substrate for citrate synthase.

Oxaloacetate: A four-carbon molecule that combines with acetyl-CoA to initiate the citric acid cycle, ultimately being regenerated to continue the cycle.

Citric Acid Cycle: Also known as the Krebs cycle or TCA cycle, it is a series of biochemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA.