The Virus

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The Virus
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What is a Virus?

• Virus Latin for Poison
• Non-cellular particle with
• DNA or RNA
• 1 or 2 Protein Coats (Capsids)
• May have Viral Envelope - Phospholipids
• DO NOT respire or grow
• ONLY function in a living cell
• NOT given Latin names like living organisms
• (rabies virus) (polio virus)
• (adenovirusadenoid tissue)

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Questions/Discussion

• Do Viruses Respire?
• What type of genetic material do viruses have?
• Can they have both DNA and RNA?

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How are they Classified?

• Shape of their protein coat (capsid)
• Important in infection
• Type of nucleic acid they contain
• DNA or RNA
• NEVER Both

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Reproduction Cycles
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How do Viruses Replicate?

• The lytic cycle
• 1- adsorption/attachment
• 2- injection/entry
• 3- replication of viral parts
• 4- assembly
• 5- release by lysis
• Results in death of host cell
• Virulent virus (only lytic cycle)

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The Steps of the Lytic Cycle
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Lysogenic Cycle

• First steps just like lytic cycle
• Does NOT destroy the host cell
• Nucleic acid joins the cells DNA. Viral DNA
  becomes a part of hosts cell DNA
• (prophage)
• Could go on for years
• Temperate virus (capable of using the lytic and
  lysogenic cycles)
• i.e. HIV, cold sores, shingles

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Lysogenic Cycle
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The Steps of the Lysogenic Cycle
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Both Cycles Together
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Types of Viruses

• Animal viruses Rabies, Polio, Mumps, Chicken
  pox, Small pox, and Influenza.
• Plant Viruses Tobacco mosaic virus (TMV),
  Banana streak virus, Carrot thin leaf virus
• Bacterial Virus Bacteriophages ( T1, T2, T3, and
  T4.)
• SPECIFIC in what type of cell and what type of
  organism they infect
• Polio human nerve cell
• T4 only certain strains of E. coli

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Different Types of Viruses

• ADENOVIRUS
• Respiratory infections colds

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Polio
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Influenza Virus

• Virus that causes the flu

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Small Pox
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TMV
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Retroviruses

• RNA viruses that contain the enzyme, reverse
  transcriptase
• This enzyme allows RNA to produce DNA
• reverse of Central Dogma (DNA ? RNA) so its
  RNA ? DNA
• HIV is an example of the virus

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Viruses Living or Not?
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Questions/Discussion

• What some differences between the lytic and
  lysogenic cycle? Similarities?
• What type of virus is HIV?
• Why do you think is HIV one of the most
  successful viruses in reproducing?