Viruses

1
Viruses

• Virus Latin for toxin or poison
• Particles of nucleic acid, protein, and sometimes
  lipids
• Enter living cells and use the cell to produce
  more viruses

2
Are viruses living?

• To be classified as living one has to
• Be made of cells
• Reproduce independently
• Have a genetic code
• Obtain and use energy
• Respond to environment
• Change over time

• Do viruses match these criteria
• No
• No
• Yes
• No
• No
• Yes

3
Viruses

• Viruses have a core of DNA or RNA surrounded by a
  protein coat
• Protein coat is called a capsid
• Enables virus to enter host cell
• Can live outside of a host in a crystallized form

4
Virus Structures Helical - plant viruses

• Tobacco Mosaic Virus infects tobacco plants

5
Virus Structures Icosohedral (spherical)
animal viruses

• Influenza virus

6
Virus Structures Complex

• T4 Bacteriophage - infect bacteria

7
Virus Structures Complex

• Poxvirus (smallpox)

8
Viral Infections

• Bacteriophages can cause two types of viral
  infections
• Lytic Virus DNA enters cell, makes new copies
  of virus, and causes lysis
• Lysis cell death, cell bursts open
• Lysogenic virus inserts DNA into DNA of host
  cell so it can replicate with the host DNA

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Lytic and Lysogenic Infections
10
Retroviruses

• Virus RNA is translated into DNA
• The DNA copy is then inserted into the host
  cells DNA
• Often remains dormant before directing production
  of new viruses
• Causes cell death
• retro- means backward

11
Human Immunodeficiency Virus (HIV) - retrovirus
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Virus Classification

• Viruses are classified according to
• the type of nucleic acid (DNA or RNA)
• Whether the nucleic acid is single or double
  stranded
• Whether the virus has an envelope
• By the type of infections that occur
• There are about 1,550 known virus species and
  about 30,000 known strains

13
Modes of transmission

• Vertical transmission (mother to child) - the
  baby is born with the virus. Ex. HIV or Hepatitis
  B
• Horizontal transmission (person to person) - most
  common
• Blood exchange, sexual activity, saliva exchange,
  breathing (aerosol affect), insect vectors, or
  contaminated food or water

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Diseases Caused by Viruses

• Common Cold Chicken Pox

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Diseases Caused by Viruses (contd)

• Herpes Simplex Hepatitis B (liver)

16
Diseases Caused by Viruses (contd)

• Polio (paralysis) Ebola (hemorrhage)

17
Vaccinations

• Help prevent infection
• Can consist of live or killed viruses
• Vaccines build up the bodys immune response for
  when the actual virus enters the body

18
Cow pox vaccination 1749

• Acquired immunization
• Artificial injection of a small amount of virus
• Bodys immune response makes antibodies