The Question is from neet-botany , and it was created by the author D VINOD

Question

A novel virus is discovered with a single-stranded nucleic acid genome.  Treatment with RNase H significantly reduces its infectivity, while DNase I has no effect.  Further analysis reveals the presence of short RNA fragments complementary to the genome. What can be most confidently inferred about the viral genome?

D VINOD · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Viral replication mechanisms and the action of nucleases.
 **Related Topics**: RNA viruses, DNA viruses, reverse transcription, RNA-dependent RNA polymerase.
 **Prerequisites**: Understanding of enzyme function (RNase H, DNase I), nucleic acid structure (ssRNA, dsRNA, DNA), and basic viral replication strategies.
## SOLUTION PATHWAY
**Given Information**:
  * The virus has a single-stranded nucleic acid genome.
  * RNase H reduces infectivity.
  * DNase I has no effect.
  * Short RNA fragments complementary to the genome are present.
**Method & Steps**:
 1. Analyze the effect of RNase H: RNase H specifically degrades the RNA strand of an RNA:DNA hybrid.  The fact that RNase H reduces infectivity strongly suggests that the virus utilizes an RNA:DNA hybrid during its replication cycle.
  Reasoning:  RNase H's action implies the presence of an RNA:DNA hybrid, a characteristic of reverse transcription.
  Formula/Rule: None directly applicable.
 2. Analyze the effect of DNase I: DNase I degrades DNA.  The lack of effect from DNase I indicates that DNA is not a primary component of the viral genome itself.
  Working:  If the genome were DNA, DNase I would reduce infectivity.
  Key Point: The absence of an effect from DNase I excludes options involving a DNA genome.
 3. Consider the complementary RNA fragments: The presence of short RNA fragments complementary to the genome suggests the existence of a double-stranded RNA intermediate during replication. This intermediate would be formed during the process of RNA replication.
  Result: The virus is most likely a single-stranded RNA virus that replicates via a double-stranded RNA intermediate.
  Verification: This explanation is consistent with all the given observations.
 ## OPTION ANALYSIS
A :x:  While it involves an RNA virus, the lack of DNase I effect contradicts a DNA intermediate.
B :x:  The DNase I result contradicts a DNA genome.
 C ✓: This option aligns perfectly with all observations: ssRNA genome, RNase H sensitivity (indicating RNA:DNA hybrid during reverse transcription, albeit not directly), and complementary RNA fragments indicating a dsRNA intermediate.
D :x: The presence of complementary RNA fragments suggests a replication step involving a double-stranded intermediate, but not necessarily a double-stranded genome.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Misinterpreting RNase H's action:  Focusing solely on RNA degradation without considering the RNA:DNA hybrid context.
  2.Ignoring the complementary RNA fragments:  Overlooking the significance of these fragments as evidence of a dsRNA intermediate.
 **Quick Tips**:
  1.Consider the specificities of the enzymes used in the experiment.
  2.Remember that many RNA viruses utilize intermediates during replication.

D VINOD · Answer

It is a single-stranded RNA virus that replicates through a DNA intermediate.

D VINOD · Answer

It is a single-stranded DNA virus that replicates through an RNA intermediate.

D VINOD · Answer

The correct Option is "It is a single-stranded RNA virus that replicates through a double-stranded RNA intermediate."

D VINOD · Answer

It is a double-stranded RNA virus.

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