Can the electron transport chain occur in the absence of oxygen? What molecule w

Question

Can the electron transport chain occur in the absence of oxygen? What molecule would build up?What molecule would be completed? What would happen to the carrier Molecule in electron transport chain? What would happen to the proton gradient? What happen to the citric cycle? So… Why do you die? Can the electron transport chain occur in the absence of oxygen? What molecule would build up?What molecule would be completed? What would happen to the carrier Molecule in electron transport chain? What would happen to the proton gradient? What happen to the citric cycle? So… Why do you die?

Explanation / Answer

Ans. O2 acts as the terminal electron acceptor during electron transport chain (ETC) in mitochondria. A functional ETC produces most of the cellular ATP upon complete oxidation of carbohydrates, fats or proteins as available and suitable depending on the relative content in the body/cell.

#I. If O2 is not present as the terminal electron acceptor, all the complexes of ETC subsequently freeze in their “reduced states” – in which they can’t oxidize and recycle NADH and FADH2.

So, ETC does NOT occur in absence of O2.

#II. Due to inhibition of ETC in absence of O2, the NADH and FADH2 molecules would not be oxidized. So, the reduced form NADH and FADH2 gradually buildup or accumulate.

#III. In absence of O2 as terminal electron acceptor, all the ETC complexes and electron carriers (CoQ, CytC) freeze in their reduced states.

So, the electron carrier also remains in their reduced state because they can’t donate their electrons to any other ETC complex.

#IV. When ETC is completely inhibited in absence of O2, the ETC becomes non-functional. A non-functional ETC can no longer create the proton gradient across the inner mitochondrial membrane.

#V. Some enzymes (dehydrogenases) of Citric acid cycle uses NAD+ and FAD as coenzymes and reduce them to NADH and FADH2 respectively during the reaction.

Since mitochondria has limited pool of NAD+/NADH and FAD/ FADH2, the reduced forms of these molecules must be oxidized for regeneration of NAD+ and FAD.

Since ETC is non-functional, NADH and FADH2 can’t be oxidized to regenerate NAD+ and FAD, thus these molecules are no longer available to the enzymes of citric acid cycle.

The depleted concertation of NAD+ and FAD further causes inhibition of dehydrogenases of citric acid cycle, and in turn, TCA itself.

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