Describe: Electron Transport System $(ETS)$ and oxidative phosphorylation.

(N/A) The respiratory process releases and utilizes the energy stored in $NADH+H^{+}$ and $FADH_{2}$. This is accomplished when they are oxidized through the electron transport system,and the electrons are passed on to $O_{2}$,resulting in the formation of $H_{2}O$.
The metabolic pathway through which electrons pass from one carrier to another is called the electron transport system $(ETS)$.
It is located in the inner mitochondrial membrane.
Electrons from $NADH$ produced in the mitochondrial matrix during the citric acid cycle are oxidized by an $NADH$ dehydrogenase $(Complex-I)$.
Electrons are then transferred to ubiquinone located within the inner membrane.
Ubiquinone also receives reducing equivalents via $FADH_{2}$ $(Complex-II)$,which is generated during the oxidation of succinate in the citric acid cycle.
The reduced ubiquinone is then oxidized with the transfer of electrons to cytochrome $c$ via the cytochrome $bc_{1}$ complex $(Complex-III)$.
Cytochrome $c$ is a small protein attached to the outer surface of the inner membrane and acts as a mobile carrier for the transfer of electrons between $Complex-III$ and $IV$.
$Complex-IV$ refers to the cytochrome $c$ oxidase complex containing cytochromes $a$ and $a_{3}$,and two copper centers.
$ATP$ formation in $ETS$:
When electrons pass from one carrier to another via $Complex-I$ to $IV$ in the electron transport chain,they are coupled to $ATP$ synthase $(Complex-V)$ for the production of $ATP$ from $ADP$ and inorganic phosphate.
The number of $ATP$ molecules synthesized depends on the nature 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 process of respiration takes place only in the presence of oxygen,the role of oxygen is limited to the terminal stage of the process. Yet,the presence of oxygen is vital,since it drives the whole process by removing hydrogen from the system.
Oxygen acts as the final hydrogen acceptor (for the production of $H_{2}O$).
In respiration,the energy of oxidation-reduction is utilized for the same process. It is for this reason that the process is called oxidative phosphorylation.