chapter6

chapter6 - Chapter 6 Virus Structure and Function General...

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Chapter 6- Virus Structure and Function General Properties of Viruses (also called virions) Obligate intracellular parasite made of nucleic acid surrounded by a protein coat. Only replicate inside host cell No nucleus, organelles, cytoplasm Viral genomes contain Information for taking over host cell (because when virus takes over host cell it must have the genes to take over) Information for making viral proteins Capsid, genome replication proteins Viroids and Prions (infections agents smaller than viruses) Viroids RNA without capsids (viruses with out capsids) just a piece of RNA Infect plants Prions Protein-only infectious agent (lacks nucleic acid) Diseases prions cause: BSE (mad cow), scrapie (sheep), Creutzfeld-Jakob, kuru (humans), chronic wasting disease (deer, elk) Defective protein causes normal protein to take on abnormal shape, loses normal function Virus Structure—Capsids (all viruses must have) Capsid- protein coat surrounding nucleic acid Capsid proteins are arranged to give virion symmetry Icosahedral capsids (poliovirus, herpes virus) Roughly spherical 20 equilateral triangles or faces filamentous capsids (M13, Ebola) Long tube of protein, with genome inside Tube made up of 100’s of identical protein subunits Tube length reflects size of viral genome Complex capsids Many bacteriophage (viruses that infect bacteria) Asymmetrical (irregular) shapes
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Tend to be larger viruses Poxviruses Virus Structure—Envelops Envelope- lipid bilayer around capsid of some viruses Allows fusion to host cell membrane (made of same material as host membrane) Only occurs if host cell not covered by cell wall Bacteriophages are NON-enveloped Envelope lipids come from host Not encoded by viral genome Proteins embedded in envelope may be encoded by virus Coats viral capsid as virus leaves cell Virus Structure—Genome (all viruses must have) DNA or RNA (genome can be made of either DNA or RNA) Includes genes encoding viral proteins Capsid Envelope proteins if virus is enveloped Any polymerase not found in host cell International Committee on Taxonomy of Viruses classification system based on several criteria: 1. Genome composition DNA or RNA Single or double stranded Linear or circular Whole or segmented (whole- just one piece; segmented- more than one piece) Classified by Baltimore method 2. Capsid symmetry Helical or icosahedral 3. Envelope - Presence or absence of host derived envelope 4. Size of virus particle - Related viruses are similar in size 5. Host range - Related viruses infect same or related hosts (some viruses are very host specific)
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Baltimore virus classification based on genome structure- see figure 6.14 Group I - Double stranded DNA - These viruses use its own or host DNA polymerase for replication - Herpesvirus group - cold sores, venereal disease, chicken pox
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This note was uploaded on 03/12/2012 for the course BIO 2051 taught by Professor Sullivan during the Spring '12 term at LSU.

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chapter6 - Chapter 6 Virus Structure and Function General...

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