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Question : What is oxidativephosphorylation ?

Answer»

Solution :The following STEPS in the respiratory process are to releaseand utilisethe energy stored in `NADH + H^(+) and FADH_(2)`
Thisis accomplished when they are oxidised through the electron transport system and theelectrons are passed on to `O_(2)`resulting in the formation of `H_(2)O`
The metabolic pathwaythrough whichthe electron passes form ONE carrier to another is called the electron transportsystem .(ETS)
It is present in the inner mitochondrialmembrane .
Electronsfrom NADH produced in the mitochondrial matrix during citric acid cycleare oxidised by an NADHdehydrogenase (Complex-I).
Electronsare then transferred to ubiquinonc location within theinner membrane.
Ubiquinone also receives reducing equivalents via `FADH_(2)` (Complex -II)
That is generated during oxidation of succinate in the citric acidcycle.
The reduced ubiquinone is then oxidised with the transfer of electronsto cytochrome c via cytochrome `bc_(1)` complex (Complex - III)
Cytochrome c is small protein attached to the other surface to the inner membrane and acts as a mobile carrierfor transfer of electrons between complexIII and IV .
Complex IV refers to cytochrome c oxidase complex containing cytochromes a and `a_(3)` and two copper centers.

ATP formation in ETS :
When the electrons pass form one carrier to another via complex I to IV in the electron transport chain, they are coupledto ATP synthase (complex V)for the production of ATP from ADP and inorganic phosphate.
The NUMBER of ATP molecules synthesised depends on thenature of the electron donor.
Oxidation of one molecule of NADH gives rise to 3 molecules of ATP, while that of one molecule of `FADH_(2)`produces 2 molecules of ATP.
Although the aerobic of respiration takes place only in the presences of oxygen .
The role of oxygen is limited tot he terminal stage of the process. Yet the PRESENCE of oxygen is VITAL, since it drives the whole process byremoving hydrogen form the system .
Oxygen acts as the final hydrogen accepter . (For production of` H_(2)` O)
In respirationit is the energy of oxidation-reduction utilised for the same process . it isfor this reason that theprocess is called oxidative phosphorylation .


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