334 QUESTION 4Number these compounds in order from lowest to highest actual physiological reduction potential. (Table 17-1 will be onlypartially helpful here - you should use your understanding of the possible paths of electrons to figure this out.)v Succinatev Coenzyme Qv Cytochrome Cv Any electron carrier in Complex IVv Any electron carrier in Complex Iv Any electron carrier Y in Complex IIIv 02v NADv FAD

Electron transport chain of mitochondria consists of four complexes termed as I, II, III and IV. The complex V associated with it is ATPase complex. The complex IV hands over the electrons to oxygen which is the ultimate acceptor in aerobic respiration.Electron transport chain has complex I as first complex. The electron carrier in it receives electrons from NADH and hands over to Complex III via coenzyme Q. Complex II (Succinate dehydrogenase complex) involves oxidation of succinate to fumarate coupled to reduction of FAD to FADH2 . Reduced FADH2 hands over its electrons to Complex III via coenzyme Q. Complex III transfers the electrons to Complex IV via cytochrome c. The reduced complex IV then reduces O2 to water. The sequence allows electrons to move from lower (more negative or less positive) reduction potential to higher (less negative or more positive) one in stepwise manner. The sequence in increasing reduction potential is NAD (lowest) < Electron carrier in complex I < Succinate < FAD < Coenzyme Q < Electron carrier in complex III < cytochrome c < Electron carrier in complex IV < O2(highest) So, the numbering can be done as: NAD (lowest) Electron carrier in complex I Succinate FAD Coenzyme Q Electron carrier Y in complex III cytochrome c Electron carrier in complex IV O2(highest)