Q.85 Which one of the following statements about gene expression is INCORRECT?
(A) DNA is transcribed to mRNA.
(B) mRNA can be reverse–transcribed to DNA.
(C) mRNA can be translated to protein.
(D) Protein can be reverse–translated to mRNA.
Option (D) is the incorrect statement about gene expression.
Gene expression follows the central dogma of molecular biology, where information flows from DNA to RNA to protein, with known biological processes supporting options A, B, and C but not D.
Option Analysis
A: DNA is transcribed to mRNA.
This describes transcription, where RNA polymerase synthesizes mRNA from a DNA template in the nucleus (eukaryotes) or cytoplasm (prokaryotes).
B: mRNA can be reverse-transcribed to DNA.
Reverse transcriptase, found in retroviruses like HIV, converts mRNA to complementary DNA (cDNA), an established exception to the strict central dogma.
C: mRNA can be translated to protein.
Translation occurs at ribosomes, where tRNA matches mRNA codons to amino acids, forming polypeptide chains.
D: Protein can be reverse-translated to mRNA.
No natural biological mechanism exists for reverse translation, as the genetic code’s degeneracy (multiple codons per amino acid) loses sequence information in proteins, preventing accurate reversal.
Gene expression incorrect statement questions test understanding of the central dogma in CSIR NET Life Sciences. This framework, proposed by Francis Crick, outlines information flow: DNA → mRNA (transcription), mRNA → protein (translation), with reverse transcription (mRNA → DNA) as a known exception. No natural reverse translation from protein to mRNA exists due to genetic code ambiguity.
Central Dogma Basics
The central dogma governs gene expression incorrect statement scenarios by restricting information flow. DNA serves as the template for mRNA synthesis via transcription. Mature mRNA then directs protein synthesis at ribosomes.
Why Reverse Translation Fails
Proteins lack codon-specific details; one amino acid matches 1-6 codons (e.g., leucine: UUA, UUG, CUU, CUC, CUA, CUG). Reverse engineering mRNA from protein sequence introduces errors, with no enzymes or ribosomes supporting this in nature. Hypothetical “reverse tRNAs” remain unproven experimentally.
CSIR NET Exam Insights
CSIR NET often features gene expression incorrect statement traps like option D. Reverse transcription is real (RT-PCR, retroviruses), but protein-to-mRNA reversal violates biological reality. Focus on exceptions: prions store no genetic info for reversal.
