Although the direct reduction of CoQ to CoQH2 is thermodynamically possible, this reaction is not a direct part of the electron transport chain via complexes I, III, and IV. Instead NADH reduces an FMN cofactor in complex I and the reduced FMNH2 kick-starts electron transport in the membrane.

Why is this electron handoff from NADH to FMN, as opposed to direct reduction of CoQ by NADH, a critical component of the electron transport chain?

This electron handoff from NADH to FMN, as opposed to direct reduction of CoQ by NADH, a critical component of the electron transport chain is important for Signaling Transduction and Metabolomics

Explanation:

The NADH-CoQ reductase reaction is catalyzed by Complex I. In this course of activity, following events takes place-  

a)FNM (NADH dehydrogenase flavoprotein) is reduced by the NADH  to FMNH2 through following reactions –  

NADH+H++E-FMN↔NAD++E-FMNH2

b)In the next phase coenzyme Q  receives electron from FMNH2  through the the iron–sulfur centers of the NADH-CoQ reductase

c)The iron atom undergoes oxidation–reduction cycles to conserve  mitochondrial protein  as lataxin and hence transport protons from the matrix to the intermembranal space thereby Signaling Transduction and Metabolomics

c. establishing proper sleep hygiene