VIRUSES

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VIRUSES
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VIRUSES

• Obligatory intracellular parasites
• Host range (organisms that they can live in)
• animals
• bacteria
• plants
• fungi
• protozoa

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Similarities between viruses and living things

• Both have DNA or RNA
• Multiply inside living cells
• Cause infection

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Differences between viruses and living things

• No cell structure
• Have a crystalline structure outside of cells

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Viral nucleic acids

• Can have DNA or RNA but not both
• Can be single stranded or double stranded
• double stranded DNA
• single stranded DNA
• double stranded RNA
• single stranded RNA
• Can be linear, circular, or several molecules

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Virus structure

• Protein coat (capsid) made of subunits called
  capsomeres
• Envelope outside capsid in some
• made of lipid, carbohydrate or protein
• some have spikes for attachment
• Size 24 - 200 nm (smaller than most bacteria
  except Mycoplasmas)

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Virus morphology

• Helical
• Polyhedral
• Enveloped
• Complex

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Classification of Viruses

• Based on
• type of nucleic acid
• method of replication
• morphology

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Culturing Viruses

• Bacteriophages grown on bacteria on agar plates
  plaques appear where bacteria are destroyed
• Live animals (must be same species as virus
  infects
• embryonated eggs
• cell culture cells form monolayer but die out
  tumor cells divide indefinitely

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Viral Multiplication

• Five stages
• attachment
• penetration
• biosynthesis of DNA/RNA protein
• maturation assembly of virions
• release

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4 Possible Outcomes of Lysogeny

• Can later return to lytic cycle
• Can transform normal bacteria into pathogenic
• Specialized transduction - prophage DNA carries
  specific genes to recipient
• Cancer induction in animal viruses (similar to
  lysogeny)