Citric acid cycle

Definition

The citric acid cycle, also known as the Krebs cycle or TCA cycle, is a crucial metabolic pathway that plays a central role in cellular respiration. It takes place in the mitochondria of eukaryotic cells and involves a series of chemical reactions that convert acetyl-CoA into carbon dioxide and energy-rich electron carriers, such as NADH and FADH2. This cycle is essential for the production of ATP, the main energy currency of the cell, linking various metabolic pathways together.

5 Must Know Facts For Your Next Test

1. The citric acid cycle begins with the condensation of acetyl-CoA and oxaloacetate to form citric acid (citrate), which is then converted through several steps back to oxaloacetate.
2. During one turn of the citric acid cycle, three NADH molecules, one FADH2 molecule, and one GTP (or ATP) are produced, along with two molecules of CO2 as byproducts.
3. The cycle is regulated by various enzymes, which can be inhibited or activated depending on the energy needs of the cell and the availability of substrates.
4. The citric acid cycle is interconnected with other metabolic pathways, such as glycolysis and fatty acid oxidation, allowing for flexibility in energy production based on cellular requirements.
5. Disruptions in the citric acid cycle can lead to metabolic disorders and are often linked to various diseases, including cancer and neurodegenerative conditions.

Review Questions

• How does the citric acid cycle contribute to cellular respiration and energy production?
  • The citric acid cycle contributes to cellular respiration by oxidizing acetyl-CoA to produce electron carriers like NADH and FADH2. These carriers then enter the electron transport chain, where their electrons are used to generate ATP through oxidative phosphorylation. This process not only provides energy for cellular activities but also produces carbon dioxide as a waste product, which is expelled from the body during respiration.
• Discuss the regulatory mechanisms of the citric acid cycle and their importance in maintaining metabolic balance.
  • The citric acid cycle is tightly regulated by various enzymes that respond to changes in cellular energy status. Key enzymes such as citrate synthase and isocitrate dehydrogenase are inhibited by high levels of ATP and NADH, signaling that energy production is sufficient. Conversely, these enzymes are activated when ADP or NAD+ levels rise, indicating a need for more energy. This regulatory balance ensures that the cycle operates efficiently according to the cell's metabolic demands.
• Evaluate the implications of dysfunction in the citric acid cycle on human health and its potential links to diseases.
  • Dysfunction in the citric acid cycle can have significant implications for human health, as it disrupts energy production and can lead to an accumulation of intermediates that may be toxic at high levels. This dysfunction has been linked to various diseases, including certain types of cancer where altered metabolism supports rapid cell growth. Additionally, neurodegenerative diseases like Alzheimer's have been associated with impaired mitochondrial function and compromised energy metabolism, highlighting how critical proper functioning of this cycle is for overall health.

Related terms

Acetyl-CoA: A key molecule in metabolism formed from carbohydrates, fats, and proteins that enters the citric acid cycle and serves as the starting substrate.

NADH: An electron carrier produced during the citric acid cycle that transfers electrons to the electron transport chain, facilitating ATP production.

Oxidative Phosphorylation: A process that occurs in the mitochondria where ATP is produced using energy derived from electron carriers like NADH and FADH2 generated during the citric acid cycle.