AP BIOLOGY

Detailed explanation-1: -The final step of the Krebs cycle regenerates OAA, the molecule that began the Krebs cycle. This molecule is needed for the next turn through the cycle. Two turns are needed because glycolysis produces two pyruvic acid molecules when it splits glucose.

Detailed explanation-2: -The transition reaction converts the two molecules of the 3-carbon pyruvate from glycolysis (and other pathways) into two molecules of the 2-carbon molecule acetyl Coenzyme A (acetyl-CoA) and 2 molecules of carbon dioxide.

Detailed explanation-3: -To start the cycle, an enzyme fuses acetyl CoA and oxaloacetate together so that citric acid is formed (a 2-carbon molecule + a 4-carbon molecule = a 6-carbon molecule!). This is the first molecule that is made in the cycle and is where the cycle gets its name.

Detailed explanation-4: -One molecule of ATP (or an equivalent) is produced per each turn of the cycle. The electron transport chain is the portion of aerobic respiration that uses free oxygen as the final electron acceptor for electrons removed from the intermediate compounds in glucose catabolism.

Detailed explanation-5: -Most of the ATP in cells is produced by the enzyme ATP synthase, which converts ADP and phosphate to ATP. ATP synthase is located in the membrane of cellular structures called mitochondria; in plant cells, the enzyme also is found in chloroplasts.