During one turn of the Krebs cycle

During one turn of the Krebs cycle (also known as the citric acid cycle or tricarboxylic acid cycle), two decarboxylation reactions occur. These decarboxylation reactions involve the removal of carbon dioxide (CO2) from the substrate molecules, resulting in the release of carbon dioxide as a waste product.

The two decarboxylation reactions occur during the conversion of isocitrate to alpha-ketoglutarate and the conversion of alpha-ketoglutarate to succinyl-CoA. Here’s a brief overview:

  1. Isocitrate to Alpha-Ketoglutarate:
  • Isocitrate (6 carbons) is converted to alpha-ketoglutarate (5 carbons) by the enzyme isocitrate dehydrogenase.
  • During this conversion, one molecule of carbon dioxide is released as a byproduct.
  1. Alpha-Ketoglutarate to Succinyl-CoA:
  • Alpha-ketoglutarate (5 carbons) is converted to succinyl-CoA (4 carbons) by the enzyme alpha-ketoglutarate dehydrogenase complex.
  • During this conversion, another molecule of carbon dioxide is released as a byproduct.

These decarboxylation reactions play a crucial role in the Krebs cycle by contributing to the generation of reducing equivalents (NADH and FADH2) and high-energy phosphate bonds (GTP/ATP), which are utilized in oxidative phosphorylation to produce ATP.

Therefore, during one complete turn of the Krebs cycle, two decarboxylation reactions occur, leading to the release of two molecules of carbon dioxide.