Question

What is the coupling effect seen in the process of NADP reduction?

Answer 1

Hint: Electron transport chain is the process during which the coupling effect is known to take place. The electron transport chain is known to comprise a series of protein complexes that transfer protons and electrons across a membrane which finally leads to ATP synthesis.

Complete answer:
In eukaryotes the electron transport chain is known to occur across the inner mitochondrial membrane. At the inner mitochondrial membrane, electrons from NADH or NADPH and $FADH_2$ pass through the electron transport chain to oxygen where they reduce it to water. The electron transport chain is known to have a series of electron donors and acceptors that donates and accepts electrons until it reaches the oxygen molecule which is the most electronegative and terminal acceptor of electrons in the chain. The passage of electrons between acceptors and donors leads to generation of a proton gradient across the intermembrane space. This gradient is utilized for the phosphorylation of ADP into ATP, a process known as oxidative phosphorylation. The reduction of NADP produces two electrons that move across the inner mitochondrial membrane. This in turn leads to generation of the proton gradient which leads to generation of ATP. The reverse of this reaction is catalyzed by enzymes known as ATPase resulting in the formation of ADP and Pi. This is known as the coupling effect.

Note:
The process of electron transport chain is essential to the cells as it causes generation of ATP which is known as the energy currency of the cell. Without ATP no major cellular processes can function.