Given below are two statements:
Statement I: In RNA interference (RNAi), a specific mRNA is silenced because a complementary dsRNA molecule binds to it and prevents its transcription.
Statement II: In RNA interference (RNAi), the complementary RNA may come from an infection by viruses having RNA genomes or from transposons that replicate via an RNA intermediate.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Statement I is incorrect but Statement II is correct.
In RNA interference (RNAi) the cell switches off one gene after its mRNA has been made. A double stranded RNA (dsRNA) that is complementary to a particular mRNA pairs with it, and that mRNA can no longer be read by the ribosome. The gene is thus silenced at the level of protein making.
Statement I: In RNA interference (RNAi), a specific mRNA is silenced because a complementary dsRNA molecule binds to it and prevents its transcription. — False. The dsRNA binds to an mRNA that is already made, so it cannot stop transcription. It prevents the translation of that mRNA. Transcription (DNA to RNA) has already taken place.
Statement II: In RNA interference (RNAi), the complementary RNA may come from an infection by viruses having RNA genomes or from transposons that replicate via an RNA intermediate. — True. These are the two natural sources of the complementary RNA. In the tobacco plant protected against Meloidegyne incognitia, the dsRNA was instead made by the plant itself from sense and anti-sense RNA of nematode-specific genes.
NCERT Extract:
Pest Resistant Plants – “… A novel strategy was adopted to prevent this infestation which was based on the process of RNA interference (RNAi). RNAi takes place in all eukaryotic organisms as a method of cellular defense. This method involves silencing of a specific mRNA due to a complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing). The source of this complementary RNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate.”