Question

The 'One gene-one enzyme' hypothesis was challenged by several researchers for its validity. The reasons are-
(A). Many enzymes are composed of more than one polypeptide encoded by different genes.
(B). Product of many genes are not enzymes
(C). Genes contain introns, which do not codes for any amino acids
(D). Several related polypeptides can be obtained from a single gene through alternate splicing
Choose the correct answer from the options given below:

• A. (A), (B) and (C) only.
• B. (B), (C) and (D) only.
• C. (A), (B), and (D) only.
• D. (A), (C) and (D) only.

Hint:

To challenge "one gene-one enzyme", look for factors that break the 1-to-1 ratio, such as: multi-subunit enzymes (A), non-enzyme products (B), and alternative splicing (D).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The "one gene-one enzyme" hypothesis, proposed by Beadle and Tatum, suggested that each gene encodes a single specific enzyme that controls a single metabolic step.
While this hypothesis was important for early genetics, subsequent molecular discoveries showed that the relationship between genes and enzymes is more complex.

Step 2: Detailed Explanation:
Let us evaluate the arguments challenging the hypothesis:
(A) is correct because many complex enzymes are oligomers composed of multiple polypeptide subunits, with each subunit encoded by a different gene (e.g., lactate dehydrogenase or hemoglobin).
This led to the revised "one gene-one polypeptide" hypothesis.
(B) is correct because many genes encode non-enzyme proteins (such as structural collagen or hemoglobin) or functional RNA molecules (such as tRNA and rRNA) that are never translated into proteins.
(C) is incorrect in this context.
While introns do not code for amino acids, their presence within eukaryotic genes does not directly challenge the functional concept that a gene's active exons map to a final protein product.
(D) is correct because alternative splicing allows a single pre-mRNA transcript to be processed into different mature mRNA isoforms, enabling a single gene to encode multiple distinct polypeptide chains.
Therefore, statements (A), (B), and (D) are the primary reasons challenging the "one gene-one enzyme" hypothesis.

Step 3: Final Answer:
The correct combination is (A), (B), and (D) only, corresponding to option (C).