key term - Citrate

Definition

Citrate is a key intermediate in the citric acid cycle, formed from the condensation of acetyl-CoA and oxaloacetate. It plays a vital role in cellular respiration by participating in energy production and connecting various metabolic pathways, including carbohydrates, proteins, and lipids.

5 Must Know Facts For Your Next Test

1. Citrate is formed when acetyl-CoA combines with oxaloacetate, creating a six-carbon molecule that undergoes further transformations in the citric acid cycle.
2. As citrate progresses through the cycle, it gets converted into several intermediates, ultimately regenerating oxaloacetate, allowing the cycle to continue.
3. Citrate not only contributes to ATP production but also serves as a signaling molecule, influencing metabolic pathways related to lipid synthesis and energy storage.
4. High levels of citrate can inhibit phosphofructokinase-1 (PFK-1), a key regulatory enzyme in glycolysis, thereby linking carbohydrate metabolism with energy production.
5. Citrate can be exported from mitochondria to the cytosol where it is cleaved by ATP-citrate lyase to produce acetyl-CoA for fatty acid synthesis.

Review Questions

• How does citrate function within the citric acid cycle and what are its implications for energy production?
  • Citrate is crucial in the citric acid cycle as it is formed when acetyl-CoA and oxaloacetate combine. This six-carbon compound undergoes a series of reactions that lead to the production of high-energy molecules like NADH and FADH2. These molecules are essential for ATP production through oxidative phosphorylation, making citrate a key player in cellular energy metabolism.
• Discuss how citrate connects various metabolic pathways, particularly regarding carbohydrates and lipids.
  • Citrate serves as a critical junction between carbohydrate metabolism and lipid synthesis. When citrate accumulates in the mitochondria, it can be transported to the cytosol where it gets converted into acetyl-CoA by ATP-citrate lyase. This conversion not only facilitates fatty acid synthesis but also links glycolytic pathways with lipid metabolism, demonstrating how different macromolecules are interconnected.
• Evaluate the regulatory roles of citrate within cellular respiration and how it impacts overall metabolic homeostasis.
  • Citrate plays a significant regulatory role in cellular respiration by influencing key enzymes involved in both glycolysis and the citric acid cycle. Elevated citrate levels can inhibit phosphofructokinase-1 (PFK-1), which slows down glycolysis when energy supplies are sufficient. This regulatory mechanism ensures metabolic homeostasis, balancing energy production and usage according to cellular demands, thereby integrating signals from carbohydrate and lipid metabolism.

Related terms

Acetyl-CoA:

A central molecule in metabolism that is derived from carbohydrates, fats, and proteins and is crucial for entering the citric acid cycle.

Oxaloacetate:

A four-carbon molecule that combines with acetyl-CoA to form citrate at the beginning of the citric acid cycle.

NADH:

An electron carrier that is produced during the citric acid cycle and plays an essential role in cellular respiration by transferring electrons to the electron transport chain.