Replication of DNA genomes

Question 1

As during cellular DNA replication, viral DNA is always synthesized by template-directed, stepwise incorporation of deoxynucleoside monophosphates (dNMPs) from deoxynucleoside triphosphate (dNTP) substrates into the 3’-OH end of the growing DNA chain.

What are the terms for where DNA replication begins and ends?

Answer 1

Replication of DNA begins and ends at specific
sites in the template

termed origins and termini respectively.

DNA polymerase enzymes is located in nucleus

Question 2

RNA polymerases can initiate synthesis de novo

What does DNA polymerase require before synthesis can begin?

Answer 2

In contrast to many RNA polymerases, no known DNA polymerase can initiate synthesis de novo: all require a primer with a free 3’-OH group

Priming of viral DNA synthesis can be via the 3’-OH terminus of RNA, a protein, or the ends of specialized structures in the genomic DNA

Question 3

Why do DNA viruses have less mutations than RNA viruses?

Answer 3

cellular and viral DNA polymerases possess proofreading capability, and have high fidelity

Question 4

Do DNA viruses need to supply their own enzymes for replication? Or can they use host machinery?

Answer 4

RNA viruses must encode enzymes that catalyse RNA-dependent RNA or DNA synthesis

DNA viruses can be replicated using cellular machinery. But retroviruses need reverse transcriptase. Benefits are that the DNA genome does not need to waste space encoding for replication proteins.

In an extreme case, poxviruses viral genome encodes complete DNA synthesis system and enzymes, so that replication can fully occur in cytoplasm of host cells