MI07: Viral Replication Synthesis

What does a successful viral infection require?

It requires a permissive cell (need its receptor for viral attachment)

What happens during a viral infection of the cell?

1. Viral mRNA must be made. (regardless of the type of viral genomic nucleic acid)

2. Virus must use cellular components and energy to synthesize proteins from mRNA

3. Must replicate its genomic nucleic acid (package in new virions)

What is the Baltimore Classification?

It is a classification system on how viral genomes get to mRNA.

What does viral RNA replication require?

It requires a viral RNA-dependent RNA polymerase.

What is + sense RNA?

It is the coding strand that functions as mRNA and can make proteins immediately.

What is - sense RNA?

It is the noncoding strang that must make complementary + sense RNA first

What type of polymerases can do viral or cellular function?

DNA polymerase and DNA-dependent RNA polymerase.

What polymerases never can do cellular function?

RNA-dependent RNA polymerase and RNA-dependent DNA polymerase.

What does DNA polymerase do?

It makes DNA from DNA template, which is provided by host cell (DNA replication). While some viruses encode their own template.

What does DNA-dependent RNA polymerase do?

It makes RNA from DNA template with host cell RNA polymerase II.

What does RNA-dependent RNA polymerase do?

It makes RNA from RNA template which must be encoded by the virus.

What does RNA-dependent DNA polymerase do?

It makes DNA from RNA template, which must be encoded by the virus using reverse transcriptase.

Where does replication occur in a DNA virus? What virus is an exception to this?

In the nucleus. Except for Poxviruses.

What type of genome do DNA viruses have?

Linear or circular genomes.

What kind of infections do DNA viruses cause?

Persistent infections

Why do RNA viruses mutate faster than DNA viruses?

RNA polymerase lacks proofreading.

Where do RNA viruses replicate their genome? What type of virus is an exception to this?

In the cytoplasm. Except for Influenza.

What type of virus are ssRNA (-) viruses?

All of these are enveloped viruses.

Why do RNA viruses need to make or bring RNA-dependent RNA polymerase?

Because cells cannot replicate RNA.

What kind of RNA and genomes do RNA viruses have?

• May be double-stranded or single-stranded RNA

• May have segmented genomes

How does the Retrovirus replicate its genome to make new copies for new infectious progeny?

RNA (+) → DNA → RNA (+)

What is an example of a virus from Retroviridae family?

HIV and Human T cell leukemia virus

How does the Retrovirus go from its genomic nucleic acid ssRNA (+) to make mRNA?

It’s virion contains reverse-transcriptase, which generates a DNA copy from RNA template.

• DNA integrates → Host cell’s DNA

• New RNA genomes are transcribed by host RNA polymerase II

What type of genome does the Retrovirus have?

RNA genome (ssRNA + genome)

What type of genome does the Hepatitis B virus have?

Circular partially dsDNA genome

How does the Hepatitis B virus replicate its genome to make new copies for new infectious progeny?

DNA → RNA → DNA

What polymerase does Hepatitis B virus need to use to go from dsDNA to making mRNA?

It uses reverse transcriptase.

• Long RNAs are transcribed

• New partially dsDNA genomes are reverse-transcribed from long RNAs