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. It is a central component of cellular respiration that produces ATP and electron carriers.

5 Must Know Facts For Your Next Test

1. The citric acid cycle occurs in the mitochondrial matrix in eukaryotes and in the cytosol in prokaryotes.
2. It generates three NADH molecules, one FADH2 molecule, and one GTP (or ATP) molecule per acetyl-CoA molecule oxidized.
3. The cycle begins with the combination of acetyl-CoA and oxaloacetate to form citrate.
4. Important intermediates include citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, and oxaloacetate.
5. Enzymes involved in the cycle include citrate synthase, aconitase, isocitrate dehydrogenase, α-ketoglutarate dehydrogenase complex, succinyl-CoA synthetase, succinate dehydrogenase, fumarase, and malate dehydrogenase.

Review Questions

• Where does the citric acid cycle take place in eukaryotic cells?
• What are the main products generated from one turn of the citric acid cycle?
• Which enzyme catalyzes the first step of the citric acid cycle?

Related terms

Glycolysis:

The process that breaks down glucose into pyruvate before entering the citric acid cycle.

Electron Transport Chain:

A series of protein complexes that transfer electrons from electron donors to electron acceptors via redox reactions.

Oxidative Phosphorylation:

The metabolic pathway where cells use enzymes to oxidize nutrients and release energy used to form ATP.