The GATE Grind

GATE 2022 BT – Question 21

Genetics, Cellular and Molecular Biology · Molecular Biology: Replication, transcription, splicing, translation, non-coding and micro RNA, RNA interference, DNA damage and repair · 1 mark · Multiple choice

In animal cells, the endogenously produced miRNAs silence gene expression by

  1. base pairing with the 3'-untranslated region of specific mRNAs
  2. blocking mRNA synthesis
  3. binding to the operator site
  4. base pairing with the 3' region of specific rRNAs

Practise this question in The GATE Grind →

Show answer and explanation

Correct answer: (A) base pairing with the 3'-untranslated region of specific mRNAs

Explanation

**microRNAs (miRNAs)** are short (about 22 nt) non-coding RNAs. In animal cells they are loaded into the RISC complex with Argonaute proteins and guide it to target mRNAs.

In animals the pairing is usually **imperfect** and located in the **3′ untranslated region (3′ UTR)** of the target mRNA. The result is translational repression and, often, deadenylation and decay of the mRNA, so gene expression is silenced.

The other options are wrong: miRNAs do not block mRNA synthesis (transcription), the operator is a bacterial DNA element, and rRNAs are not their targets.

Answer **A**.