VIRUSESVIRUSESCHAPTER 18CHAPTER 18

Part 1

CharacteristicsCharacteristics

• non-living particlesnon-living particles• invade living cellsinvade living cells• pathogenic - named pathogenic - named

after the disease they after the disease they cause or organ they cause or organ they infectinfect

• smallest of all smallest of all organismsorganisms

T-4 Virus - infects E. coli

VIRUS - an obligate VIRUS - an obligate intracellular parasite intracellular parasite

INFECTIOUS MONONUCLEOSIS

Origin of VirusesOrigin of Viruses

• Viruses may have Viruses may have originated from host originated from host cellscells

• 1935 - first seen by 1935 - first seen by an electron an electron microscope microscope

• Tobacco mosaic Tobacco mosaic virus - first virus virus - first virus discovered - 1886discovered - 1886 Wendell Stanley (1904 -

1971) first isolated TMV in 1935.

1886 - “Living Fluid Infectant” - the virus passed through filters that held

bacteria.

Viral StructureViral Structure

• Inner core - Inner core - contains viral DNA contains viral DNA or RNA (never or RNA (never both)both)

• Capsid - outer coat Capsid - outer coat of proteinof protein

• Envelope - outer Envelope - outer layer on larger layer on larger virusesviruses

http://glencoe.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=mov::196::240::/sites/dl/free/0078802849/181977/e21_1int.mov

Click on the link above

Various Shapes of Viruses

Viral ReplicationViral ReplicationLytic CycleLytic Cycle

• 1. Attachment 1. Attachment • 2. Injection2. Injection• 3. Replication3. Replication• 4. Assembly4. Assembly• 5. Lysis5. Lysis

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LYSOGENIC CYCLELYSOGENIC CYCLE

1. Attachment1. Attachment2. Injection2. Injection3.3. Viral DNA Viral DNA

integration integration (provirus) (provirus)

4. Cell division4. Cell division5. Replication5. Replication6. Assembly6. Assembly7. Lysis7. Lysis

VIRUSESVIRUSESCHAPTER 18CHAPTER 18

Part 2

Edward Jenner - Edward Jenner - discovered a vaccine for smallpoxdiscovered a vaccine for smallpox

SmallpoxSmallpoxVariola (Major & Minor)Variola (Major & Minor)

• First virus to be First virus to be studied in detailstudied in detail

• Edward Jenner - Edward Jenner - 17981798

• First vaccine - First vaccine - cowpox virus cowpox virus (vaccinia virus)(vaccinia virus)

Child with smallpoxChild with smallpox

Last caseLast case of smallpox of smallpox(Ali Maow of (Ali Maow of Merka, Somalia, Merka, Somalia, contracted contracted smallpox in 1977 smallpox in 1977 at the age of 23. at the age of 23. His was the last His was the last known case of known case of smallpox in the smallpox in the world.)world.)

Icosahedral Virus

(many sides)

Wart virusPolio - Naked, small, icosahedral virus

Enveloped VirusEnveloped Virus

INFLUENZA VIRUS

Children with measles Children with measles (uncommon today)(uncommon today)

BACTERIOPHAGEBACTERIOPHAGE

E-Coli Bacteria

Attachment of a phage to Attachment of a phage to the cell wall of E-Coli the cell wall of E-Coli

Temperate vs. Virulent VirusesTemperate vs. Virulent Viruses

HERPES ZOSTER HERPES ZOSTER (“Shingles”)(“Shingles”)

HERPESHERPES VIRUSVIRUS

HERPES

RetrovirusesRetroviruses

• RNA virusesRNA viruses• Reverse Reverse

transcriptase - transcriptase - makes DNA from makes DNA from its RNAits RNA

• Includes HIV, Includes HIV, polio & some polio & some cancerscancers

HIV

Retrovirus CycleRetrovirus Cycle

HIV /HIV /AIDSAIDS

Louis Pasteur - discovered a vaccine for rabies

Animal Rabies in U. S.Animal Rabies in U. S.19991999