[Campbell Biology P.216] Based on Figure 9.3, what is the key structural difference observed... | Practice Question

Based on Figure 9.3, what is the key structural difference observed in the nicotinamide portion when NAD+ is reduced to NADH?

  • A: The addition of a phosphate group.
  • B: A change from a 6-membered ring to a 5-membered ring.
  • C: The addition of an extra hydrogen atom to the carbon adjacent to the nitrogen, resulting in the neutralization of the positive charge on nitrogen.
  • D: The removal of a carboxyl group.

Explanation

Figure 9.3 clearly illustrates the difference: NAD+ has a positive charge on the nitrogen atom in its nicotinamide ring. Upon reduction to NADH, an extra hydrogen atom is added to the carbon adjacent to this nitrogen, and the nitrogen's positive charge is neutralized.