Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).

Assertion (A): During evolution, some species, including humans, became dependent on dietary vitamin C due to loss of their ability to biosynthese ascorbic acid (AA) on their own.
Reason (R): The loss of ability for the biosynthesis of ascorbic acid in human is due to the inactivation of an important enzyme viz. L-Gulono-Lactone Oxidase (GLO).

In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

The inactivation of the GULO gene occurred approximately 63 million years ago in the common ancestor of haplorhine primates.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Vitamin C (ascorbic acid) is a vital antioxidant and cofactor for collagen synthesis. While most vertebrates can synthesize it from glucose, some mammalian lineages have lost this metabolic pathway.

Step 2: Detailed Explanation:
Assertion (A) is correct because humans, other anthropoid primates, guinea pigs, and some bats cannot synthesize vitamin C and must obtain it from their diet to prevent scurvy.
Reason (R) is correct because the biosynthetic pathway for ascorbic acid from glucose is highly conserved, ending with the oxidation of L-gulonolactone.
This final step is catalyzed by the enzyme L-gulonolactone oxidase (GLO).
During primate evolution, the gene encoding GLO (GULO) acquired major mutations, turning it into a non-functional pseudogene.
Because humans lack a functional GLO enzyme, they cannot complete the synthesis of ascorbic acid, which directly explains their dietary dependency.

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).