What Is RNA Interference (RNAi) and How Genes Are Silenced?
Biology · Biotechnology and Its Applications · NEET
RNA interference (RNAi) is a natural cell defence in all eukaryotes that switches OFF a specific gene by stopping its mRNA from making protein. A double-stranded RNA (dsRNA), made complementary to the target mRNA, binds that mRNA and prevents its translation. Memory hook: "dsRNA glues the mRNA shut" — silencing means the mRNA cannot be read, so no protein is made.
Sense and anti-sense RNA pair to form dsRNA, which binds the target mRNA and blocks translation. The result is a silenced gene with no protein made, while the DNA gene stays intact.
Your doubts, answered
Does RNAi silence at the DNA level or the mRNA level?
At the mRNA level. The gene (DNA) is still present, but its mRNA is blocked before translation, so no protein is made. NCERT calls this 'silencing of a specific mRNA'. This is why the effect is called gene silencing, not gene deletion.
Why is dsRNA needed and not ssRNA?
RNAi is triggered by a complementary double-stranded RNA (dsRNA). A sense RNA and an anti-sense RNA pair up to form dsRNA, which then binds the target mRNA and stops its translation. NEET repeatedly tests that genes are silenced using ds-RNA (2019 Odisha), not ss-RNA, ss-DNA or ds-DNA.
Where does the complementary RNA come from naturally?
NCERT says the source can be an infection by viruses that have RNA genomes, or mobile genetic elements (transposons) that replicate through an RNA intermediate. The cell uses RNAi against these, which is why RNAi is described as a method of cellular defence.
What are sense and anti-sense RNA in the nematode strategy?
In the transgenic plant, the introduced DNA is made to produce both a sense RNA and an anti-sense RNA. Because they are complementary, they pair to form dsRNA. This dsRNA starts RNAi and silences the nematode's specific mRNA, so the parasite cannot survive.
Is RNAi only in plants?
No. RNAi takes place in all eukaryotic organisms as a natural method of cellular defence. In biotechnology it is used to make pest-resistant plants (for example, against the nematode Meloidogyne incognita in tobacco).
⚠️ The NEET trap ✗ Students pick ds-DNA or ss-RNA as the silencing molecule, or think RNAi removes/mutates the gene in the DNA. ✓ Genes are silenced using ds-RNA (double-stranded RNA), which binds a specific mRNA and prevents its translation. The DNA gene stays intact; only its mRNA is silenced. 🧠 dsRNA, not dsDNA — and it blocks mRNA, it does not cut DNA.
Real NEET questions
2019
In RNAi, the genes are silenced using:
A · ds-RNA ✓
B · ss-DNA
C · ss-RNA
D · ds-DNA
Solution: RNA interference silences a specific mRNA through a complementary double-stranded RNA (dsRNA) that binds the target mRNA and prevents its translation. In the nematode-resistance strategy, sense and anti-sense RNAs pair to form this dsRNA. So genes are silenced using ds-RNA (option A).
2020
Match the columns and select the correct option. Column-I: (a) Bt cotton (b) Adenosine deaminase deficiency (c) RNAi (d) PCR. Column-II: (i) Gene therapy (ii) Cellular defence (iii) Detection of HIV infection (iv) Bacillus thuringiensis
A · (a)-(ii), (b)-(iii), (c)-(iv), (d)-(i)
B · (a)-(i), (b)-(ii), (c)-(iii), (d)-(iv)
C · (a)-(iv), (b)-(i), (c)-(ii), (d)-(iii) ✓
D · (a)-(iii), (b)-(ii), (c)-(i), (d)-(iv)
Solution: Bt cotton uses the toxin gene of Bacillus thuringiensis (a-iv). The first gene therapy treated adenosine deaminase (ADA) deficiency (b-i). RNAi is a method of cellular defence in eukaryotes (c-ii). PCR is used to detect HIV in suspected AIDS patients (d-iii). This gives option C. Note RNAi = cellular defence is the key match tested here.
Solved Biotechnology and Its Applications NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
RNAi is a cellular defence in all eukaryotes that silences a specific mRNA using a complementary dsRNA, so the target protein is not made.
Which molecule silences the gene in RNAi?
A double-stranded RNA (dsRNA). It is formed when complementary sense and anti-sense RNAs pair up, and it blocks translation of the target mRNA.
Is the gene destroyed in RNAi?
No. The DNA gene stays intact. Only its mRNA is blocked (silenced), so no protein is produced from it.
How is RNAi used to make pest-resistant plants?
Using Agrobacterium, nematode-specific genes are put into the plant so it makes both sense and anti-sense RNA. These form dsRNA that silences the nematode's mRNA, so the parasite cannot survive in the transgenic plant.
Why is RNAi called a cellular defence?
Cells use RNAi against RNA viruses and transposons that make RNA. By silencing their mRNA, the cell defends itself, so RNAi is a natural defence found in all eukaryotes.
