Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
Which one of the following bacteriophages has a genome composed of single
stranded circular DNA?
Options:
(A) ØX174
(B) λ
(C) T5
(D) P1
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2024 Q.21)**
**1. Governing Concept**:
- **Topic**: Virology & Bacteriophage Genome Architecture
- **$\Phi$X174** is a well-characterized microvirus (Microviridae) featuring a **single-stranded circular DNA** (ss(+)DNA) genome of 5,386 nucleotides (the first DNA genome ever sequenced, by Sanger in 1977).
- Bacteriophages $\lambda$, T5, and P1 possess double-stranded linear DNA genomes.
**2. Option Analysis**:
- **Option (A) [ØX174] is CORRECT**: Possesses a circular single-stranded DNA genome.
- **Option (B) [λ] is INCORRECT**: Lambda phage contains a linear double-stranded DNA genome with cohesive single-stranded 12-nt *cos* ends.
- **Option (C) [T5] is INCORRECT**: Linear double-stranded DNA phage with site-specific nicks.
- **Option (D) [P1] is INCORRECT**: Linear double-stranded DNA phage that circularizes after infection via terminal redundancy and Cre-lox recombination.
**3. Final Answer**:
- **Correct Choice**: **A**
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