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Virus Genome Replication

LECTURE 12:. Virus Genome Replication. Waqas Nasir Chaudhry. Viro100: Virology 3 Credit hours NUST Centre of Virology & Immunology. Transcription of virus genomes. There are four main categories of virus genome: dsDNA , ssDNA , dsRNA and ssRNA

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Virus Genome Replication

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  1. LECTURE 12: Virus Genome Replication WaqasNasirChaudhry Viro100: Virology 3 Credit hours NUST Centre of Virology & Immunology

  2. Transcription of virus genomes • There are four main categories of virus genome: dsDNA, ssDNA, dsRNA and ssRNA • Because of distinct modes of transcription within the dsDNA and ssRNA categories a total of seven classes of viruses can be recognized • This division of the viruses into classes based on genome type and mode of transcription was first suggested by David Baltimore

  3. (+) or (−) Genome • This labelling is relative to the virus mRNA, which is always designated (+). • A nucleic acid strand that has the same sequence as mRNA is labelled (+) and a nucleic acid strand that has the sequence complementary to the mRNA is labelled (−)

  4. Some DNA viruses have ability to carry out reverse transcription; these viruses known as pararetroviruses and Class VII was formed to accommodate them i.e. Badnavirus of plants

  5. Ambisense Genome There are a few single stranded nucleic acids of viruses where there is a mixture of (+)and(−) polarity within the strand, in other words there are open reading frames (ORFs) in both directions. Example Sendai Viruses

  6. Modifications to the central dogma • In 1958 Francis Crick proposed a ‘central dogma of molecular biology’ • Which stated that the flow of genetic information is always from DNA to RNA and then to protein, with genetic information transmitted from one generation to the next through copying from DNA to DNA

  7. ‘central dogma of molecular biology’

  8. Increasing understanding of how viruses replicate their genomes necessitated some modifications to this dogma in 1970; many viruses have RNA genomes that are copied to RNA, and some viruses copy from RNA to DNA Modifications to the central dogma

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