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Dna Viruses
1. DNA VIRUSES-Dnavirus is a virus that has DNA (deoxyribonucleic acid) as its genetic material. -They are usually Large, Icosahedral, enveloped in Lipoproteins-Do not have polymerase enzymes, and cause Latent infection-Examples include Poxviruses, Herpesviruses, hepadnaviruses, Hepatitis b.
2. HERPESVIRUSES -Larger virions than adenoviruses(180 - 200nm)-Larger genome (three to five times) than adenoviruses. -Linear, double-stranded DNA, Enveloped, icosahedral virus (this means that lipid solvents readily inactivate these viruses)
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4. Adsorption and penetration-Many herpesviruses, including herpes simplex virus, can fuse directly with the plasma membrane (results in partial uncoating). -Such fusion with the plasma membrane has implications for both the virus and the host cell.
5. Earlyphase-Early transcription (the mRNAs made during this phase are the alpha and beta mRNAs). -Herpes viruses use host RNA polymerase-The virus uses host mRNA modification enzymes.-Initially, alpha-mRNAs are transcribed-Beta-mRNAs are transcribed by the host RNA polymerase again-Beta proteins are involved in gene expression regulation-They decrease alpha-gene expression and are needed for gamma gene expression.
6. Late phase-Herpesvirusescode for several proteins, in addition to the DNA polymerase, that are needed for DNA replication. -DNA replication is accompanied by a lot of recombination-The replicated DNA is present as long concatamericmolecules-These are cleaved to genome-size lengths when DNA is packaged into the virion.
7. Late transcription: -Late transcription occurs after DNA replication. -Gamma mRNAs are made and are translated in the cytoplasm. -Gamma proteins are predominantly structural. -There is decreased expression of beta genes in the late stage. -In herpes viruses there is no apparent organization of the genome into blocks for either early or late transcription.
8. Assembly-Assembly occurs in the nucleus. -A capsid is formed and the DNA enters the capsid. -The capsids acquire an envelope by budding through areas of the inner nuclear membrane which have viral membrane proteins inserted into them. -The virus envelope then fuses with the outer nuclear membrane and the de-enveloped nucleocapisid is delivered into the cytoplasm -It then becomes re-enveloped by budding into Golgi-derived vesicles and is then released.-The late protein required for transcription of immediate early mRNAs in the next round of infection is packaged in the virion.