Question

What is the role of ${ NAD }^{ + }$ in cellular respiration?
(a) It is a nucleotide source for ATP synthesis.
(b) It functions as an enzyme.
(c) It is the final electron acceptor for anaerobic respiration.
(d) It functions as an electron carrier.

Answer 1

Hint: During cellular respiration, ${ NAD }^{ + }$ becomes NADH which means it is getting reduced. A compound is said to have undergone a reduction reaction when H gets added to it. Or when electrons are added to a compound.

Complete answer:
The role of ${ NAD }^{ + }$ is that it acts as an electron carrier. It accepts electrons from compounds by oxidizing them and adds H+ as well to give NADH. NADH is a reducing agent which then gives these electrons at the ETS. These electrons then flow through a series of complexes which result in the production of ATPs. By the process of ETS, 3 ATP molecules are generated by the oxidation of one NADH. This process is called oxidative phosphorylation.

So, the correct answer is the option ‘It functions as an electron carrier’.

Additional information:
Let us know more about this vital compound in our body.
NAD (Nicotinamide Adenine Dinucleotide) is a coenzyme which means that it helps enzymes function properly. It is present in all living cells and is involved in metabolism. ${ NAD }^{ + }$ has two functions:
- Act as an electron and hydrogen carrier to produce energy from food.
- Act as coenzymes help enzymes catalyze chemical reactions in our bodies.
NAD is formed by simple amino acids like tryptophan, aspartic acid, etc, and a vitamin ${ B }_{ 3 }$ called niacin. It exists in the body as two forms i.e. ${ NAD }^{ + }$ (oxidizing form) and NADH (reducing form). The structure of NAD consists of two nucleotides attached by phosphate groups, hence the name dinucleotide.

Note: Not to be confused with nicotinamide adenine dinucleotide phosphate (NADP) which mainly plays a role in photosynthesis. The trick to remember, associate the P of NADP with photosynthesis. In ETS, NADH gives its electrons to Complex-I (NADH dehydrogenase) whereas its contemporary FADH gives its electrons to Complex- II (cytochrome ${ bc }_{ 1 }$).