Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
The type of nucleic acid present in phage is
Options:
(A) base pairing with the 3'-untranslated region of specific mRNAs
(B) blocking mRNA synthesis
(C) binding to the operator site
(D) base pairing with the 3' region of specific rRNAs
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2022 Q.18)**
**1. Governing Concept**:
- **Topic**: Virology & Temperate Bacteriophage $\lambda$
- Bacteriophage lambda ($\lambda$) possesses a **linear double-stranded DNA** genome of 48.5 kb packaged in its icosahedral capsid.
- The linear genome has 12-base complementary single-stranded 5' overhangs at both ends called **cohesive (*cos*) sites**, which allow the DNA to circularize immediately upon injection into the host *E. coli* cytoplasm.
**2. Option Analysis**:
- **Option (A) [double-stranded DNA] is CORRECT**: Phage $\lambda$ contains a linear dsDNA genome with cohesive ends.
- **Option (B) [single-stranded DNA] is INCORRECT**: Characteristic of filamentous phages (M13, fd) and $\Phi$X174.
- **Option (C) [double-stranded RNA] is INCORRECT**: Characteristic of *Cystoviridae* ($\Phi$6).
- **Option (D) [single-stranded RNA] is INCORRECT**: Characteristic of *Leviviridae* (MS2, Q$\beta$).
**3. Final Answer**:
- **Correct Choice**: **A**
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