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RNA Interference

RNA interference is a cellular mechanism in which double-stranded RNA prevents expression of a specific gene by degrading or blocking its complementary messenger RNA.

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Student-friendly explanation

RNA interference, or RNAi, is a gene-silencing process. When double-stranded RNA matching a particular gene is present in a cell, it is processed into small interfering RNA molecules. These guide a protein complex to complementary mRNA, causing that mRNA to be degraded or preventing its translation. In biotechnology, this natural defence-like mechanism can be used to silence a harmful gene in a pest or parasite. The NCERT-style example is nematode-resistant tobacco, where RNAi prevents Meloidogyne incognita from surviving properly in the host plant. The exam focus is the relation between dsRNA, complementary mRNA, and gene silencing.

How to write this in exams

  1. 1

    Start with the exact idea

    RNA interference is a cellular mechanism in which double-stranded RNA prevents expression of a specific gene by degrading or blocking its complementary messenger RNA.

  2. 2

    Then show how to use it

    State that RNAi is gene silencing, mention dsRNA, explain formation of small interfering RNA, show pairing with complementary mRNA, then explain mRNA degradation and loss of protein production.

  3. 3

    Add one concrete example

    In tobacco plants, genes corresponding to an essential nematode gene are introduced in a way that produces dsRNA. When Meloidogyne incognita infects the plant, the nematode gene is silenced, reducing its ability to survive.

  4. 4

    Avoid this incomplete answer

    RNAi kills the nematode by directly destroying its DNA.

Definition

RNA interference is a cellular mechanism in which double-stranded RNA prevents expression of a specific gene by degrading or blocking its complementary messenger RNA.

Example

In tobacco plants, genes corresponding to an essential nematode gene are introduced in a way that produces dsRNA. When Meloidogyne incognita infects the plant, the nematode gene is silenced, reducing its ability to survive.

Rule to remember

Key rule: RNAi is sequence-specific because the small RNA guides silencing only when it is complementary to the target mRNA.

Memory hook

RNAi: interfering RNA finds matching mRNA and stops the message.

Examples and method

Worked example

Question: Explain RNAi with the tobacco-nematode example. Answer: A nematode-specific gene sequence is introduced into tobacco so the plant produces dsRNA. This dsRNA triggers RNAi when the nematode feeds on the plant. The complementary nematode mRNA is silenced, so the parasite fails to make an essential protein.

Method to apply

State that RNAi is gene silencing, mention dsRNA, explain formation of small interfering RNA, show pairing with complementary mRNA, then explain mRNA degradation and loss of protein production.

Diagram support

A process diagram may show dsRNA formation, cutting into siRNA, binding to complementary mRNA, and mRNA degradation. Labels: dsRNA, siRNA, target mRNA, silencing complex, blocked protein synthesis.

How CBSE asks it

Commonly asked as a short answer on mechanism, an assertion-reason item about dsRNA and mRNA silencing, or an application question using nematode-resistant tobacco.

Avoid common mistakes

Common confusion

Students often write that RNAi changes the DNA sequence. RNAi usually silences gene expression at the RNA level rather than editing the DNA.

Common wrong answer

RNAi kills the nematode by directly destroying its DNA.

Exam tip

Use the words double-stranded RNA, complementary mRNA, degradation, and gene silencing in the same answer.

Quick check

How does RNA interference protect tobacco plants from Meloidogyne incognita?

RNA interference protects tobacco by producing dsRNA that matches an essential nematode gene. This leads to degradation or blocking of the nematode mRNA, so the required protein is not made and the parasite cannot survive normally.

Answer writing and exam use

1-mark answer

Define RNAi, mention dsRNA, describe complementary mRNA targeting, explain degradation or blocked translation, and apply it to Meloidogyne-resistant tobacco.

2-mark answer

Define RNAi, mention dsRNA, describe complementary mRNA targeting, explain degradation or blocked translation, and apply it to Meloidogyne-resistant tobacco.

3-mark answer

Define RNAi, mention dsRNA, describe complementary mRNA targeting, explain degradation or blocked translation, and apply it to Meloidogyne-resistant tobacco.
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