AP BIOLOGY

Detailed explanation-1: -First, acetyl CoA combines with oxaloacetate, a four-carbon molecule, losing the CoA group and forming the six-carbon molecule citrate. After citrate undergoes a rearrangement step, it undergoes an oxidation reaction, transferring electrons to NAD+ to form NADH and releasing a molecule of carbon dioxide.

Detailed explanation-2: -For each acetyl CoA that enters the citric acid cycle, two carbon dioxide molecules are released in reactions that are coupled with the production of NADH molecules from the reduction of NAD+ molecules.

Detailed explanation-3: -The removed carbon molecule combines with oxygen to produce CO 2start subscript, 2, end subscript. Some of the energy, in the form of electrons, is captured in formation of high-energy compound, NADH.

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: -The citric acid cycle is a key metabolic pathway that connects carbohydrate, fat, and protein metabolism. The reactions of the cycle are carried out by eight enzymes that completely oxidize acetate (a two carbon molecule), in the form of acetyl-CoA, into two molecules each of carbon dioxide and water.