Bio Ch 19

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Bio Ch 19
2011-05-05 17:44:58

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  1. Viral Genomes
    • •Viral genetic material is variable
    • –Double-stranded DNA (dsDNA)
    • –Single-stranded DNA (ssDNA)
    • –Double-stranded RNA (dsRNA)
    • –Single-stranded RNA (ssRNA)
    • •Either DNA or RNA virus respectively
    • From 4 genes to several hundred genes
  2. Capsids
    • •Capsid is the protein shell
    • –Shape is variable (rod, polyhedral, etc.)
  3. Envelopes
    • •Viral envelope may surround capsid
    • –Derived mostly from membrane of host cell
    • •Lipid bilayer (host) with proteins (virus/host)
    • –Envelope may help cloak virus in host system
    • –Allows virus to enter host cell more easily
    • •Envelope fuses w/ host plasma membrane
    • –New viruses emerge in new envelopes
  4. Viral specificity
    • •Can only reproduce within certain host
    • •Each virus has limited host rang
    • –Can only infect certain host cells
    • •Viruses recognize receptors on host cells
    • •Host range can be single or many species
    • –Ex. Swine flu (pigs & humans), rabies (mammals)
    • •Viruses can be tissue specific
    • Ex. Cold virus affects upper respirators
  5. Virus reproductive cycle
    • Entry and uncoating
    • –Viral genome inserted into host cell
    • –Viral genome alters host cell activity
    • 2. Replication of viral genome
    • –Viral hereditary material copied
    • –Using host nucleotides, enzymes etc.
    • 3.Replication of viral proteins (capsid)
    • w/ host enzymes, ribosomes, amino acids etc.
    • 4.Assembly & release of new viruses
    • –100s-1000s of viruses produced by host
    • –Results in cell damage and/or death
    • •Host cell often destroyed
    • •Contributes to virus symptoms
  6. retroviruses
    • –Use reverse transcriptase enzyme
    • –Transcribes DNA from RNA template
    • –New DNA (viral) then integrates into nucleus
    • –ex. HIV targets certain lymphocytes à AIDS
  7. Viral Diseases
    •Severity depends on target tissue–Ex. cold virus affects respiratory epitheliu•Cells can divide and/or repair themselves–Ex. polio virus attacks nerves•Nerve cells do not divide, permanently damaged•Vaccines–Harmless varieties or portions of microbe•ex. Cowpox used to vaccinate against smallpox–Creates immunological memory