The tricarboxylic acid cycle, also known as the citric acid cycle or Krebs cycle, is a series of chemical reactions that occur in living organisms to generate energy through the oxidative breakdown of acetyl-CoA, a molecule derived from carbohydrates, fats, and proteins. It plays a vital role in cellular respiration, the process by which cells convert nutrients into usable energy in the form of adenosine triphosphate (ATP).
The cycle takes place in the mitochondria of eukaryotic cells and in the cytoplasm of prokaryotes. It involves a sequence of eight enzymatic reactions that result in the complete oxidation of acetyl-CoA, producing carbon dioxide, reducing equivalents in the form of NADH and FADH2, and a small amount of ATP.
The tricarboxylic acid cycle starts with the condensation of acetyl-CoA with a four-carbon molecule called oxaloacetate, forming a six-carbon molecule known as citrate. Through a series of redox reactions, citrate is eventually converted back into oxaloacetate, completing a cycle. Along the way, three molecules of NADH, one molecule of FADH2, and one molecule of GTP (which can be converted into ATP) are produced.
Besides its role in energy production, the tricarboxylic acid cycle also serves as a hub for metabolic pathways, as many other molecules can enter and exit the cycle. This enables the cycle to participate in various biosynthetic processes such as the generation of amino acids, nucleotides, and other important cellular components.
