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MCAT Question A Day - 8/10/13 - Answer!

What do NAD, FAD, and the cytochromes all have in common?

A.  Each is reduced.
B.  Each is oxidized.
C.  Each is reduced and oxidized.
D.  Each acts as an oxygen carrier.

The correct answer is (C). NAD, FAD, and the cytochromes are all hydrogen acceptors (electron acceptors) that first accept (reduction) and then pass along (oxidation) their hydrogens (or electrons). None of these molecules act as “oxygen carriers.” Oxygen is the final hydrogen (or electron) acceptor in the electron transport chain.