The GATE Grind

GATE 2021 BT – Question 21

Recombinant DNA Technology and Other Tools in Biotechnology · Molecular tools: Site-directed mutagenesis, CRISPR-Cas, biosensors, interaction tools, genomics and proteomics approaches · 1 mark · Multiple choice

CRISPR-Cas is associated with

  1. adaptive immunity in eukaryotes
  2. adaptive immunity in prokaryotes
  3. innate immunity in eukaryotes
  4. innate immunity in prokaryotes

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Show answer and explanation

Correct answer: (B) adaptive immunity in prokaryotes

Explanation

**CRISPR-Cas** is the system by which bacteria and archaea defend themselves against viruses (phages) and plasmids.

**How it works.**
1. The cell stores short pieces of invader DNA (**spacers**) in its CRISPR array. This is a record of past infections, i.e. a "memory".
2. The array is transcribed into guide RNAs.
3. If the same invader returns, the guide RNA directs the Cas nuclease to the matching DNA and cuts it.

A defence that remembers specific past invaders and responds specifically to them is **adaptive immunity**, and it occurs in **prokaryotes**. Answer **B**.