Arrange the sequence of events for the overall mitochondrial respiratory assembly in the correct order.

1) Coenzyme Q-cytochrome c reductase passes electrons to cytochrome c.

2) Coenzyme Q releases its electrons to complex III.

3) Cytochrome oxidase catalyzes the reduction of O2 to water.

4) Succinate, through complex II, and NADH, via complex I, release electrons to coenzyme Q.

A. 4, 1, 3, 2
B. 4, 3, 1, 2
C. 4, 1, 2, 3
D. 4, 2, 1, 3

Option D, 4,2,1, 3

Explanation:

The mitochondrial respiratory chain (MRC) comprises of four membrane bound complexes and it involves the following steps

a)RC complexes (RCC) I and II reduces the RC’s equivalent where RCCI i.e receives electron from the NADH.  

b)These electrons are then transferred to the flavin mononucleotide factor and then passed on to the Fe-S embedded cluster .

c)These electron reduces the coenzyme Q  to ubiquinol  

d)With in the inner mitochondrial membrane (IMM), protons are trans located from IMM to the  intermembrane space (IMS)

e)RC complex II then transfer electron from succinate to the cofactor FAD

f)From FAD proton are transferred to the FeS cluster and on the other hand electron move from QH2 to the RC complex III

g)This RC complex III give its electrons to the cytochrome and they are further passes on to the RC complex IV

h)With four redox centers, the terminal RC complex translocate protein by using energy produced in electron transfer thereby converting oxygen into water.

Hence, the correct option is D

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