Question

Which of the following is true for replicative form of single stranded viral DNA

• A. All the single stranded viral DNA become double stranded
• B. Half of the viral DNA become double stranded DNA
• C. All the DNAs are converted to RNA
• D. Half of the viral DNA become double stranded DNA and another half become RNA

Hint:

To transcribe viral proteins and replicate, ssDNA viruses must first convert their genomes into double-stranded DNA (Replicative Form), as host RNA polymerase can only utilize double-stranded templates.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Single-stranded DNA (ssDNA) viruses (such as the bacteriophages \(\Phi\text{X174}\) and M13) must replicate their genomes inside a host cell using host replication machinery, which requires a double-stranded template.

Step 2: Detailed Explanation:
Upon entering the host cell:
- The circular single-stranded viral DNA (designated as the (+) strand) is recognized by host replication enzymes.
- The host machinery synthesizes a complementary (-) strand, converting the entire single-stranded viral genome into a double-stranded circular DNA molecule.
- This fully double-stranded circular form is called the Replicative Form (RF) or RF DNA.
- This RF DNA serves as the template for both viral mRNA transcription and subsequent rolling-circle replication to package new ssDNA genomes.
- Therefore, all invading single-stranded viral genomes are converted to double-stranded RF DNA.

Step 3: Final Answer:
All the single stranded viral DNA become double stranded, corresponding to option (A).