Question

One molecule of $NAD{H_2}$​ on oxidation yields ______ ATP molecules.
a. One
b. Two
c. Three
d. Four

Answer 1

Hint: The cycles of respiration results in the production of $NAD{H_2}$ and $FAD{H_2}$. Glycolysis and the Krebs cycle are two major processes that are responsible for production of these molecules. Further oxidation of these molecules takes place via the electron transport system.

Complete answer:
Formation of ATP occurs when the electrons are transferred to ${O_2}$ from $NAD{H_2}$ or $FAD{H_2}$ through a sequence of electron carriers. This process is known as the oxidative phosphorylation. Mitochondria is the site of this reaction. Majorly the formation of ATP occurs via this process. It takes place during aerobic respiration. Glycolysis and the Krebs cycle are the processes that are majorly responsible for the formation of $NAD{H_2}$ and ​ $FAD{H_2}$. These molecules further are oxidized through the process of electron transport chain. This system is characterized by the donation of the electrons from donor to acceptor. Oxidation of these products occurs and a proton gradient is created which helps in the formation of ATP molecules. Transfer of electrons from $NAD{H_2}$ to complex I takes place which pumps 4 protons. These electrons are then further transferred to the complex III which further pumps 4 protons and then to complex IV which pumps two protons. So, in total 10 protons are pumped. 1 ATP is synthesized using 4 protons; approximately 3 ATPs are produced from one $NAD{H_2}$ molecule.

Hence, the correct answer is option (C), That is one molecule of $NAD{H_2}$​ on oxidation yields 3 ATP molecules.

Note: In Eukaryotes, oxidative phosphorylation occurs in the mitochondria. This process is highly dependent on the transfer of electrons. Four complexes are present in the respiratory chain and synthesis of ATP occurs via proton gradient.