AP BIOLOGY

Detailed explanation-1: -Isocitrate is oxidized and decarboxylation occurs with a carbon dioxide molecule released. The coenzyme NAD+ is reduced to form another dinucleotide, NADH.

Detailed explanation-2: -Step 8: In the last step of the Krebs cycle, malate is converted to oxaloacetate. In the process, NAD+ is reduced to form NADH + H+.

Detailed explanation-3: -The oxidation of pyruvic acid results in the reduction of NAD+, production of Ac-S-CoA and a molecule of CO2, as shown below. The Krebs cycle functions during respiration to oxidize Ac-S-CoA and to reduce NAD+ and FAD to NADH and FADH2 (respectively).

Detailed explanation-4: -So using this information, we can tally up the total amount of reduced NAD produced by one turn of the Krebs cycle. Our correct answer is three molecules of reduced NAD are produced.

Detailed explanation-5: -The cellular respiration processes of all living cells make use of the coenzyme Nicotinamide adenine dinucleotide (NAD). It plays a key role in energy metabolism by accepting and donating electrons. The low energy form NAD+ shown at left is raised to the high energy form NADH.