Question

The oxidative phosphorylation is-
A) Addition of phosphate group in ATP
B) Formation of ATP from electrons removed during substrate oxidation
C) Formation of transfer of phosphate group from substrate to ADP
D) Oxidation of phosphate group in ATP

Answer 1

Hint: Oxidative phosphorylation takes place in the inner mitochondrial membrane. Phosphorylation is the addition of a phosphoryl group to a molecule. In biological systems, this reaction is important for the cellular storage and transfer of free energy using energy carrier molecules present inside the cell.

Complete answer:
Adenosine 5’-triphosphate (ATP), the most abundant energy carrier molecule in the living system, has two high-energy phosphate phosphate bonds that can be broken to release free energy when the cell needs it to perform various cellular processes. Likewise, excess free energy can be used in synthesis of ATP via the phosphorylation of adenosine 5’-diphosphate (ADP), effectively storing it as chemical energy for later use. The conversion of ADP to ATP can occur through two kinds of phosphorylation reactions: oxidative phosphorylation and substrate-level phosphorylation.
During oxidative phosphorylation, energy released during the oxidation of nutrients by enzymes is used to drive various energy-requiring phosphorylation reactions occuring in the body (i.e. oxidation and phosphorylation are coupled). Energy is captured as electrons are transferred from electron donors to electron acceptors, such as oxygen, in a series of reduction-oxidation (redox) reactions occuring in the inner mitochondrial membrane. This energy is ultimately by an ATP-synthesizing enzyme called ATP synthase through a process called electron transport. Oxidative phosphorylation is highly efficient, but only occurs under aerobic conditions, it does not occur in anaerobic conditions.
The electron transport chain and chemiosmosis together make up oxidative phosphorylation. The key steps of this process are-
Reduced electron carriers (NADH and $FAD{H}_2$) from other steps of cellular respiration transfer their electrons to molecules near the beginning of the transport chain; these molecules are electron acceptors.
In the process, they themselves turn back into $NA{D}^{+}$ and FAD, which can be reused in other steps of cellular respiration.
 As electrons are passed through the chain, they move from a higher to a lower energy level, releasing energy.
Some of the energy is used to pump $H^{+}$ ions, moving them out of the matrix and into the intermembrane space which establishes an electrochemical gradient.
At the end of the electron transport chain, electrons are finally transferred to molecular oxygen, which splits in half and takes up $H^{+}$ to form water.
As $H^{+}$ ions flow down their gradient and back into the matrix, they pass through an enzyme called ATP synthase, which helps in synthesis of ATP.

Thus, the answer for the above question is B- Formation of ATP from electrons removed during substrate oxidation.

Note:
Although oxidative phosphorylation is an important part of metabolism, it produces reactive oxygen species such as superoxide and hydrogen peroxide, which lead to propagation of free radicals, damaging cells and contributing to disease and, possibly, aging and senescence which is a very dangerous outcome.