Question

In the replication of phage containing positive-sense DNA,

a) The host's enzymes are used to make dsDNA.
b) The host's DNA polymerase uses the phage RNA as a template to make negative-sense DNA.
c) A phage-encoded DNA polymerase is used to make negative-sense RNA using the phage positive-sense RNA as a template.
d) A phage-encoded DNA polymerase is used to make DNA using the phage positive-sense RNA as a template

Answer 1

In the replication of a phage containing positive-sense DNA, the host cell's enzymes are used to create dsDNA, which is then transcribed to mRNA used for the assembly of new virions. Retroviruses with +ssRNA utilize reverse transcriptase to create cDNA, and subsequently, dsDNA, which can integrate into the host genome.

Step-by-step explanation:

For a DNA virus, or a phage in this context, host enzymes are typically employed to synthesize double-stranded DNA (dsDNA), which can then be transcribed into messenger RNA (mRNA) and further translated into proteins. This process allows for the assembly of new virions. In the case of RNA viruses, and specifically, retroviruses that contain positive-sense single-strand RNA (+ssRNA), there is a unique process involving the viral enzyme reverse transcriptase. This enzyme reverse transcribes the +ssRNA into complementary single-strand DNA (cDNA), which is then used to create dsDNA, potentially integrating into the host cell's genome as a provirus and allowing chronic infection. In contrast, RNA viruses with a negative-sense single-strand RNA (-ssRNA) genome require transcription into +ssRNA by viral RNA-dependent RNA polymerase (RdRP) before translation can occur. The fact that retroviruses like HIV produce unique enzymes, such as reverse transcriptase, for their replication cycle has led to targeted drug treatments that specifically inhibit these viral enzymes.