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chapter 19, viruses (emerging viruses (viruses burst on to the human scene…

- - - - some mutations change existing viruses into new genetic varieties
    - - ex: AIDS went unnoticed until it began to spread
    - - animals that carry a virus are unaffected by it, and are considered natural reservoir for the virus
      - ex: swine flu, from pig to human
  - - - different strains of A are given names
        
        name identifies tell us which form of two viral proteins are present, hemagglutinin (H), and neuraminidase (N)
        
        (H) there are 16 different types, a protein that helps the flu virus attach to the host
        
        (N) there are 9 types, enzyme that helps release new virus particles from infected cells
- - - - (2) the (ER) and the Golgi apparatus have cellular enzymes which add sugars
      - (3) resulting viral glycoproteins. embedded in the membrane derived from the host cell are transported tot eh cells surface
      - (4) new viral capsids are wrapped in membrane as they bud from the cell
      - (5) the enveloped viruses are free to infect other cells
      - the replicative cycle don't kill the host cell
  - - - genome class of IV viruses serve as mRNA and are translated into viral protein after infection
        
        class V, the RNA genome serves instead as a template for mRNA synthesis
        
        the RNA genome is transcribed into RNA strands, functioning as mRNA and as a template for synthesis of additional copies of genomic RNA
        
        viruses that use RNA genome as template for mRNA transcription require RNA to RNA synthesis
    - - virus equipped with an enzyme called reverse transcription
        
        transcribes the RNA template into DNA, RNA to DNA information flow the opposite of the usual direction
        
        ex: HIV that causes AIDS
- - - - a plant becomes more vulnerable to viral infection if it was damaged by wind, injury or herbivores
      - herbivores are a threat b/c the act as carriers of viruses
    - - occur in asexual propagation or in sexual reproduction
- - - - a DNA virus or an RNA virus based on the nucleic acid that makes up the genome
  - - - influenza virus has a membranous envelope that surrounds the capsid
    - - the capsids have icosahedral heads that enclose the DNA, attached to the head is a protein tail piece that have fibers in which the phages attach to a bacterial cell
- - - - typical signs are abnormal development and stunted growth
  - - - the prions convert the normal proteins to the misfolded prion
        
        prion aggregation interferes with normal cellular functions and cuases disease symptoms