Chapter 18.2 Viruses and Prions

“Viruses and prions are smaller and less complex than bacteria;

they invade cells and can alter cellular

functions.”

Chapter 18.2 Learning Targets• Illustrate the general structure of viruses.

• Compare and contrast the sequence of events in viral replication by the lytic cycle, the lyosgenic cycle, and retroviral replication.

• Discuss the structure, replication, and action of prions in relationship to causing disease.

Characteristics

• non-living particles• invade living cells• pathogenic - named after

the disease they cause or organ they infect

• smallest of all organisms

T-4 Virus - infects E. coli

VIRUS - an obligate intracellular parasite

INFECTIOUS MONONUCLEOSIS

Origin of Viruses

• Viruses may have originated from host cells

• 1935 - first seen by an electron microscope

• Tobacco mosaic virus - first virus discovered - 1886

Wendell Stanley (1904 - 1971) first isolated TMV

in 1935.

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

bacteria.

Viral Structure

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

• Capsid - outer coat of protein

• Envelope - outer layer on larger viruses

Various Shapes of Viruses

Viral ReplicationLytic Cycle

• 1. Attachment • 2. Injection• 3. Replication• 4. Assembly• 5. Lysis

LYSOGENIC CYCLE

1. Attachment2. Injection3. Viral DNA

integration (provirus)

4. Cell division5. Replication6. Assembly7. Lysis

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VirusesBozeman Biology

http://www.youtube.com/watch?v=L8oHs7G_syI

8:06 min.

VIRUSESCHAPTER 18

Part 2

Edward Jenner - discovered a vaccine for smallpox

SmallpoxVariola (Major & Minor)

• First virus to be studied in detail

• Edward Jenner - 1798• First vaccine - cowpox

virus (vaccinia virus)

Child with smallpox

Last case 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 Virus

INFLUENZA VIRUS

Children with measles (uncommon today)

BACTERIOPHAGE

E-Coli Bacteria

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

Temperate vs. Virulent Viruses

HERPES ZOSTER (“Shingles”)

HERPES VIRUS

HERPES

Retroviruses

• RNA viruses• Reverse transcriptase

- makes DNA from its RNA

• Includes HIV, polio & some cancers

HIV

Retrovirus Cycle

The Immune SystemBozeman Biology

http://www.youtube.com/watch?v=L8oHs7G_syI

13:47 min.

HIV /AIDS

When HIV Becomes AIDS (HIV #2)

http://www.youtube.com/watch?v=68I7JlVhuhY

3:56 min

Louis Pasteur - discovered a vaccine for rabies

Animal Rabies in U. S.1999