RNA & DNA virus general rules

Question 1

What is the general rule for most DNA viruses?

Answer 1

Most DNA viruses depend on the cellular RNA polymerase II, the enzyme that produces cellular mRNA.

Most DNA viruses replicate in the nucleus.

DNA viruses use cellular or viral DNA polymerases to replicate their genomes.

Question 2

What is the exception to the general rules for DNA viruses?

Answer 2

Poxviruses are transcribed by viral DNA dependent RNA polymerase and viral accessory proteins because they replicate in the cytoplasm.

Question 3

What can +ssRNA act as in host cells?

Answer 3

mRNA

Therefore if you can get the +SSRNA into the host cell, this alone can initiate viral replication and growth.

Question 4

What is the general rule for -ssRNA and dsRNA?

Answer 4

-ssRNA and dsRNA viruses carry enzymes in their virions to produce +ssRNA to be translated by cellular machinery. Naked -ssRNA and dsRNA are therefore non-infectious.

Question 5

What is the general rule for all RNA viruses?

Answer 5

All RNA viruses , except retroviruses, encode an RNA-dependent RNA polymerase to catalyze synthesis of new genomes and mRNA.

Question 6

what is the general rule for +ssRNA viruses?

Answer 6

•+ssRNA viruses do not carry a viral RNA polymerase in the viral particle. Protein is translated from +ssRNA to produce enzymes: therefore +ssRNA alone is infectious.

Question 7

what does retroviruses have?

Answer 7

RNA directed DNA polymerase (reverse transcriptase RT) : makes double stranded DNA to insert into the genome of the cell. Viruses have 50-100 molecules of RT in their capsid. Hepadna viruses (DNA virus) also have RT.

Question 8

why does RNA dependent RNA poly show a high mutation frequency?

Answer 8

partly because of a lack of a proofreading function that assures fidelity in other processes such as DNA replication.
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RNA dependent DNA polymerase (reverse transcriptase) may be even more error prone.