Question

One gene-one enzyme hypothesis is not universal because
A. Many enzymes are composed of polypeptides encoded by different genes
B. Many genes encodes non-enzymatic protein
C. rRNA, tRNA, etc., are product of genes but not enzyme
D. One gene may codes for more than one enzyme through alternate splicing
E. Gene mutation creates metabolic pathway block
Choose the correct answer from the options given below:

• A. A-B-C-E only
• B. B-D-E-C only
• C. A-C-D-E only
• D. A-B-C-D only

Hint:

One Gene-One Enzyme was revised to One Gene-One Polypeptide because genes encode multimeric subunits, structural proteins, non-coding RNAs, and splice variants.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
George Beadle and Edward Tatum (1941) proposed the 'One Gene-One Enzyme' hypothesis in Neurospora crassa.

Step 2: Detailed Explanation:
The hypothesis was subsequently modified to 'One Gene-One Polypeptide' and 'One Gene-One Transcript' due to four major molecular realities:
1. Heteromultimeric proteins (A): Many enzymes consist of multiple distinct polypeptide subunits encoded by separate genes (e.g., hemoglobin $\alpha_2\beta_2$, RNA polymerase core).
2. Non-enzymatic proteins (B): Structural proteins, antibodies, and peptide hormones are encoded by genes but are not enzymes.
3. Non-coding functional RNA genes (C): Genes transcribing rRNA, tRNA, snRNA, and microRNAs do not code for proteins or enzymes.
4. Alternative pre-mRNA splicing (D): A single eukaryotic gene locus can produce multiple distinct polypeptide isoforms via alternative exon splicing.
(Statement E was the experimental proof supporting the original hypothesis, not an exception).

Step 3: Final Answer:
Hence, statements A, B, C, and D only explain why the hypothesis is not universal.