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DNA VIRUSES-Dnavirus is a virus that has DNA (deoxyribonucleic acid) as its genetic material. -They are usually Large, Ico...
HERPESVIRUSES -Larger virions than adenoviruses(180 - 200nm)-Larger genome (three to five times) than adenoviruses. -Linea...
Adsorption and penetration-Many herpesviruses, including herpes simplex virus, can fuse directly with the plasma membrane ...
Earlyphase-Early transcription (the mRNAs made during this phase are the alpha and beta mRNAs). -Herpes viruses use host R...
Late phase-Herpesvirusescode for several proteins, in addition to the DNA polymerase, that are needed for DNA replication....
Late transcription: -Late transcription occurs after DNA replication. -Gamma mRNAs are made and are translated in the cyto...
Assembly-Assembly occurs in the nucleus. -A capsid is formed and the DNA enters the capsid. -The capsids acquire an envelo...
Evolution of Viruses:<br /><ul><li>Viral genomes undergo genetic change by mutation, either spontaneous or induced mutatio...
Recombination may be either intramolecular or, among viruses with divided genomes, by reassortment.</li></li></ul><li>1.Mu...
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Dna Viruses

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Dna Viruses

  1. 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. <br />
  2. 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)<br />
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  4. 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. <br />
  5. 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.<br />
  6. 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.<br />
  7. 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.<br />
  8. 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. <br />
  9. 9. Evolution of Viruses:<br /><ul><li>Viral genomes undergo genetic change by mutation, either spontaneous or induced mutation, and by recombination.
  10. 10. Recombination may be either intramolecular or, among viruses with divided genomes, by reassortment.</li></li></ul><li>1.Mutations:<br />These arise naturally during viral replication<br />2. Exchange of Genetic material:<br />This involves breaking of covalent bonds within the nucleic acid, exchange of genetic information, and reforming of covalent bonds. <br />This kind of break/join recombination is common in DNA viruses or those RNA viruses which have a DNA phase (retroviruses). <br />The host cell has recombination systems for DNA. If a virus has a segmented genome and if two variants of that virus infect a single cell, progeny virions can result with some segments from one parent, some from the other.<br />

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