Ch. 6

• virion


  complete virus particle, consists of one RNA or DNA enclosed in protein, but may have other layers; cannot reproduce independently or carry out cell division
• virus classification


  genome, life cycle, morphology, and relatedness
• virus types


  bacteriophages, archaeal, and eukaryotic (most common)
• nonenveloped


  nucleocapsid consisting of DNA/RNA and protein coat
• enveloped


  envelope, spikes, nucleocapsid
• virus size


  10 - 400 nm, must be viewed with electron microscope
• capsid


  protein coat of virus, made of protomers; protects genetic material and aids in transfer to hosts
• helical capsid


  protomers self-assemble to form hollow tube with protein walls, size is determined by nucleic acid
• icosahedral capsid


  polyhedron made of capsomers (units of 5/6 protomers)
• envelope


  outer membranous flexible layer (arises from host in animals), proteins project from surface as spikes or peplomers
• enzymes


  most lie within capsid, some are in envelope
• genome


  single or double stranded DNA/RNA, length varies and can be segmented or circular
• viral multiplication


  attachment -> entry -> uncoat genome -> synthesis -> assembly -> release
• attachment (multiplication)


  specific receptors, determine host preference
• entry and uncoating (multiplication)


  capsid fuses with membrane to enter, or uses endocytosis via vesicle; injects nucleic acid
• synthesis(multiplication)


  genome dictates events, RNA viruses must carry in or synthesize proteins they need
• assembly (multiplication)


  usually in stages in bacteriophages, occurs in the cytoplasm or the nucleus
• release (multiplication)


  nonenveloped viruses lyse the host cell and proteins attack the cell wall/membrane; enveloped viruses use budding
• virulent phages


  reproduce immediately upon entry, lyse host cell
• temperate phages


  reproduce as virulent phages do, or remain in the host cell and integrate their genome through lysogeny (changes phenotype of host)
• archaeal viruses


  may be virulent (lytic) or temperate
• cytocidal infection (eukaryotes)


  lyses host
• persistent infections (eukaryotes)


  cause cytopathic effects (abnormalities, degenerative changes, cancer via activation of oncogene)
• carcinogenesis


  oncogenes may come from virus or may be host transformed ones; herpes, hep B, hep C, HPV, HTLV1
• plaque


  areas of destruction and lyse on agar cultures infected with virus
• cultivation of viruses


  young, actively growing bacteria in broth or agar; broth loses turbidity and plates form plaque as infection takes hold
• counting viral particles


  direct or indirect (plaque assay: # of plaques in PFU/ml)
• viroids


  closed, circular ssRNA's; do not encode gene products and require host cell RNA polymerase to replicate
• satellites


  nucleic acids (DNA or RNA); encode their own capsid with help of a helper virus; Hep D with Hep B helper
• prions


  PrPc (normal) is converted into an abnormal form by PrpSc; all diseases have no treatment, are fatal, and result in neural degeneration (mad cow, kuru, CJD, scrapie)