AP BIOLOGY

Detailed explanation-1: -Simplified diagram of the citric acid cycle. First, acetyl CoA combines with oxaloacetate, a four-carbon molecule, losing the CoA group and forming the six-carbon molecule citrate.

Detailed explanation-2: -The remaining steps of the Krebs cycle regenerate oxaloacetic acid from succinate: Succinate is oxidized to form the four-carbon molecule called fumerate.

Detailed explanation-3: -In the presence of oxygen, acetyl CoA delivers its acetyl group to a four-carbon molecule, oxaloacetate, to form citrate, a six-carbon molecule with three carboxyl groups.

Detailed explanation-4: -Why is the 4-carbon compound generated in the breakdown of citric acid the only permanent compound in the Krebs cycle? It is regenerated at the end of each complete turn of the cycle.

Detailed explanation-5: -Citric acid or citrate is a 6 carbon molecule that is produced when acetyl-CoA joins with a 4 carbon molecule called oxaloacetate to enter the Krebs cycle. For this reason the Krebs cycle is often referred to as the citric acid cycle.