Question

Redraw Figure 19.8 to show the replicative cycle of a virus with a single-stranded genome that can function as mRNA (a class IV virus).

Short answer

RNA viruses contain three types of single-stranded RNA in their genome. Class V viruses RNA strand serves as the template for the synthesis of mRNA that produces proteins and other copies of RNAs. This is depicted in figure 19.8.

The genome in class IV viruses works like an mRNA and can produce viral proteins when it infects the host cell.

Step-by-step solution

Class IV virus

Animal viruses are divided into six classes according to the type of genetic machinery used by the viruses. Class IV viruses contain a single-stranded RNA genome that can work directly as mRNA.

Host ribosomes can read the mRNA for translation, and viral proteins are produced in the host. An example is coronavirus.

Step 2: mRNA

mRNA is the type of RNA that has a nucleotide sequence corresponding to the sequence of the DNA in a cell. It contains codes that are read by ribosomes during translation. The transcription process is required to synthesize this molecule using DNA as a template and enzyme RNA polymerase.

Step 3: Replicative cycle of class IV viruses

Class IV viruses are different from class V viruses in having a single-stranded RNA genome used directly as mRNA. As the virus enters the host cell, its genome starts the production of viral proteins by using host ribosomes.

It also produces RNA-dependent RNA polymerase, which creates more RNA copies. After assembling positive sense RNA and viral proteins, new viral progenies are released.