Question 29 from UPSC CSE 2019 - Science & Technology

Question

What is Cas9 protein that is often mentioned in news?

Accepted Answer

Correct Option: A. A molecular scissors used in targeted gene editing

Strategy: Focus on the context from current affairs—Cas9 is always seen in gene-editing discussions linked to CRISPR. The core identifier is 'molecular scissors': Cas9 cuts DNA at targeted locations, enabling gene modifications. Options mentioning biosensor, pest resistance, or herbicide are unrelated to the mechanism or scientific purpose of Cas9, allowing easy elimination.

Key Info: **What is Cas9?**
Cas9 is an endonuclease enzyme central to the CRISPR-Cas9 gene editing technology. CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a natural defense mechanism in bacteria, allowing them to remember and disable viral DNA. Scientists leverage this system for programmable, site-specific modification of DNA in diverse organisms.

**Mechanism of Action**
The Cas9 protein, guided by a synthetic RNA molecule (guide RNA), binds to complementary DNA sequences and makes double-stranded breaks at targeted locations, effectively acting as 'molecular scissors.' This process allows for the deletion, insertion, or replacement of genetic material.

**Applications**
CRISPR-Cas9 technology has revolutionary applications in several fields:
- **Medicine:** Gene therapy and correction of genetic diseases.
- **Agriculture:** Development of genetically modified crops.
- **Research:** Fundamental biological research.

**Key Distinctions**
Cas9 is not a biosensor, a gene for pest resistance, or a herbicidal substance.

**Research and Institutions**
CRISPR-Cas9 has been widely reported in scientific advancements, including the first gene-edited babies in 2018. Leading institutions involved in CRISPR research include the Broad Institute (MIT and Harvard) and the Max Planck Institute.

Answer

Option B: A biosensor used in the accurate detection of pathogens in patients

Answer

Option C: A gene that makes plants pest-resistant

Answer

Option D: A herbicidal substance synthesized in genetically modified crops