Question

32) p 217. When electrons flow from the NAD+/NADH redox pair to the
O2/H2O redox pair, does the reaction begin with NAD+ or with NADH? What is produced, O2 or H2O?

33) p 217. Name and briefly describe the major electron carriers involved in respiration that are found in cells. Consider the two forms of the coenzyme NAD/NADH. Is 'NADH' or 'NAD' the better electron donor?

Answer 1

32. During respiration, electrons are released from NADH and FADH2 and eventually are transferred to O2, forming H2O according to the following overall reactions:

33. NAD and FAD are used as electron carriers to temporarily store energy during cellular respiration.

electron carrier is basically a molecule that transports electrons during cellular respiration. By using electron carriers, energy harvested from glucose can be temporarily stored until the cell can convert the energy into ATP.

NAD+ is aromatic while NADH is not. Aromatic compounds are more stable than its standard counterparts due to delocalization of pi electrons. Thus energy input is required to convert to NADH; it has a higher free energy.
Hence NAD is better electron donor.