Chapter 3-Virus Structure(2) (1).ppt

Chapter 3-Virus Structure(2) (1).ppt - Virus Structure...

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Virus Structure Chapter 3
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Outside the host cell, a virus survives as a virus particle- known as virion A virion is a “gene delivery system”- it contains the virus genome, and it functions to protect the genome and to aid its entry into the host cell In the host cell the genome can be replicated and packaged into new virions The genome is packaged in a protein structure known as the capsid Many viruses also have a lipid component- generally present at the surface of the virion- an envelope- the viruses without envelope are described as naked The envelope also contains proteins that function in aiding the virus to enter the host cell Some viruses form protective protein occlusion bodies around Basics of virus structure Remember the terms in red- what they mean and how they are spelled, these are new scientific terms used in viro
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Virus Genomes A virion contains the virus genome in the form of one or more molecules of nucleic acid For any one virus the genome could be either DNA or RNA For any new virus that is isolated, one can determine the composition of its genome by determining its susceptibility to DNase or RNase Each nucleic acid molecule is either single-stranded or double- stranded, giving 4 categories of virus genomes dsDNA, ssDNA, dsRNA, ssRNA The dsDNA viruses encode their genes in the same manner as animals, plants, bacteria and other cellular systems Other 3 types of genomes are unique to viruses Most fungal viruses: dsRNA, most plant viruses: ssRNA, most bacterial viruses: dsDNA genomes
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Figure 2.0.11: Types of viral nucleic acid genomes.
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Polarity and Polymerases
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Further categorization of Virus Genomes Is the genome linear with free 3’ and 5’ ends? Or is it circular as a result of the nucleic acid strand being covalently closed? Some linear molecules can be in a circular conformation as a result of pairing between complementary sequences at their ends - e.g. DNA in hepadnavirus and RNA in influenza virus. At this point, no need to memorize this, we study the genomes in detail with specific viruses late
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Genome Sizes of some DNA viruses and Cells Remember these viral genome sizes
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Segmented Genomes More common among RNA viruses than DNA viruses ssRNA: influenza viruses- package the segments in the same virion, brome mosaic virus- packages the segments in different virions- we will not study in detail but an interesting fact dsRNA: reoviruses Provides the virus with the possibility of new gene combinations and thus rapid evolution- we will study this for influenza virus Repeat sequences Many viruses have genomes that contain repeat sequences- they constitute promoters, enhancers, origins of replication, etc Linear genomes have repeats at the ends- terminal repeats - direct or inverted
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Virus Proteins Tobacco mosaic virus: only one protein species!
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  • Spring '18
  • virion, Basics of virus structure

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