2. Viruses Discovery of Viruses Berijerinck Wendell Stanley Edward Jenner
(1897)
coined the Latin name "virus"  meaning poison for  the substance infecting tobacco plants
Wendell Stanley
(1935) crystallized sap from tobacco leaves infected with Tobacco Mosaic Virus (TMV)
first person to see virus
found virus was made of nucleic acid & protein
Edward Jenner
(1796) developed smallpox vaccine
used pus from cowpox

3. Viruses Discovery of Viruses - Continued Louis Pasteur Sabin Salk
Developed second vaccine against anthrax
Developed third vaccine against rabies
Used dried spinal cord of a rabbit
Sabin
Developed vaccine against polio that contained live virus
Given orally
Salk
Developed vaccine against polio using killed virus
Given as shot

4. Viruses Virology - study of viruses
Deadly viruses are said to be virulent
Viruses couldn't be seen until electron microscope invented
Viruses cause disease by
Killing cells
Changing the rate of mitosis (warts, tumors, and cancer)

5. Wendell Stanley and Leaf with TMV

6. Viral Characteristics
Not living organisms
Noncellular
Consist of
a nucleic acid core (DNA or RNA)
a protein coat called the capsid
Some have a plasma membrane
Capsid made of protein subunits called capsomeres
Cannot grow or replicate on their own (inactive particles)

7. Viral Characteristics
Can only reproduce inside of a living host cell using its raw materials & enzymes
Lack ribosomes & enzymes needed for protein synthesis or metabolism
Are extremely small particles ranging from nanometers on average
Some can cause disease (smallpox, measles, mononucleosis, influenza, colds, AIDS, Ebola)

8. Viral Characteristics
Some may also cause cancers such as leukemias
Virus free cells are rare
Highly host specific (only infect certain cells)
Referred to as phages
Viruses are classified into 2 main groups by their nucleic acid --- DNA or RNA Viruses
 DNA & RNA viruses are subdivided by capsid shape & whether they do or don't have an envelope

9. Viral Structure
DNA or RNA core surrounded by protein sheath called capsid
Nucleocapsid  includes the viral nucleic acid & its capsid
Some form lipid rich covering around capsid called the envelope
Envelope usually formed from host cell membrane
Envelope may have spikes to help chemically recognize & attach to the host cell

10. Viral Structure TMV is helical
Adenovirus & polio viruses are icosohedral (20 sided)

11. Viral Structure
T-phages have a head and a tail

12. Bacteriophage or T-phage
Among the most complex viruses
Attack bacterial cells
Composed of a icosohedral head, tail, base plate, & tail fibers
Long DNA molecule is inside the head 
Tail helps inject the viral DNA into host cell
Tail fibers used to attach to host

13. Retrovirus Contain RNA
Have an enzyme called reverse transcriptase which helps use the RNA to make DNA
Use the host cell's ribosomes & raw materials to make viral proteins
Cause some cancers & AIDS
HIV Virus

14. Lytic Cycle Phases of the Lytic Cycle of a Virulent Virus:
Absorption: Virus attaches itself to the cell.
Entry: Enzymes weaken the cell wall and nucleic acid is injected into the cell, leaving the empty caspid outside the cell. Many viruses actually enter the host cell intact.
Replication: Viral DNA takes control of cell activity.
Assembly: All metabolic activity of the cell is directed to assemble new viruses.
Release: Enzymes disintegrate the cell in a process called lysis, releasing the new viral particles

15. Lytic Cycle
Source:

16. Lysogenic Cycle The Lysogenic Cycle of a Temperate Virus:
The virus attaches itself and injects its DNA into the cell.
The viral DNA attaches itself to the host DNA, becoming a new set of cell genes called a prophage.
When the host cell divides, this new gene is replicated and passed to new cells. This causes no harm to the cell, but may alter its traits.
Now there are two possibilities:
The prophage survives as a permanent part of the DNA of the host organism.
Some external stimuli can cause the prophage to become active, using the cell to produce new viruses.

17. Source: http://science.howstuffworks.com/virus-human.htm
Lysogenic Cycle
Source:

18. Viral Control Interferon are proteins made by cells to fight viruses
Two types of viral vaccines exist --- inactivated & attenuated
Inactivated virus vaccines don't replicate in the host's system
Attenuated viral vaccines have been genetically altered so they can't cause disease
Antiviral drugs (AZT, acyclovir, & azidothymidine) interfere with viral DNA synthesis
Protease Inhibitors interfere with viral capsid production
New viruses emerge as rain forests are cleared (Ebola virus)

19. Adenovirus
Common cold
Influenza Virus
Note-plasma
membrane

20. HIV
Coronavirus
SARS

21. Classification By Nucleic acids By Structure By Speed of Infection
By Specificity

22. Classify By Nucleic Acid in Core DNA Viruses
DNA inserted into host cell is incorporated into the host genome.
Host cell does not differentiate
Viral DNA commandeers control and signals host to replicate viral DNA and to produce viral protein.
Host uses itself up to produce these
Result is a hollow sack of viral particles.

23. Classify By Nucleic Acid in Core RNA Viruses
RNA is inserted into the cell
Host cell is signaled to make viral RNA and viral protein
Result is the same for host cell
DEATH

24. Polio virus is a RNA virus

25. Classify By Nucleic Acid in Core Retrovirus Viruses
Nucleic acid is RNA but with the addition of enzyme-Reverse Transcriptase
Enzyme allows production of DNA from viral RNA
RNA->DNA->RNA->Protein
Does this disprove the Central Dogma?
Lab use of reverse transcriptase

26. RNA
Reverse transcriptase
HIV is a retrovirus

27. Classify By Specificity
Viruses are extremely specific as to which kinds of cells they parasitize
Identify protein receptors on the outside of host cells
Tobacco mosaic virus does not infect animals or bacteria.
The viral protein determines the specificity

28. Classify By Speed Lytic viruses attack the host cell quickly
Lysogenic or latent viruses insert the nucleic acid and lie dormant.
Unknown chemical signals activate them
They may never be activated
If host cell divides the viral genome is replicated along with other DNA

29. Mutation Viral nucleic acids can mutate
Sometimes pick up parts of host DNA
Sometimes pick up host membrane
Three types of pathogens that have no vaccines
Retroviruses
Those with multiple antigens
Those that mutate rapidly
HIV is a retrovirus with many antigens that mutates rapidly.

30. Origin of Viruses Hypothesis 1. Viruses predate first cells
Hypothesis 2. Viruses are cellular fragments
Evidence for 2 is that some viruses wrap their DNA around histones to form nucleosomes as eukaryotic cells
Viruses have followed own evolutionary path.

31. Viroids and Prions: The Ultimate in Simplicity
Plant Viroid
Prion

32. Viroids Naked RNA found in plant cells Infectious agents
Process of infection a mystery
As is replication
May interfere with gene regulation

33. Prions Naked protein not associated with a nucleic acid
Infectious agent
Action unknown
Identified as cause of
scrapie--sheep
mad cow--bovine
C-J—humans

34. Unicellular Prokaryotes
Bacteria
Unicellular
Prokaryotes
Point of a straight pin
with thousands of
bacterial cells

35. History Leeuwenhoek Louis Pasteur Robert Petri
Probably first person to see bacteria
Louis Pasteur
Father of bacteriology
First person to study bacteria extensively
Robert Petri
Developed the petri dish
Used to culture bacteria

36. Koch’s Postulates
A formalized group of criteria for establishing the cause of an infectious disease
The microorganism must be present in every case of a disease.
The organism must be grown in pure culture from diseased hosts.

37. Koch’s Postulates continued
The same disease must be produced when a pure culture of the organism is introduced into susceptible hosts.
The organism must be recovered from the experimentally infected host.

38. Koch’s bacterial discovery
1876
Convincing proof of “germ theory” of disease
Showed that Bacillus anthracis is cause of anthrax
Often fatal disease in humans, sheep and other animals

39. Koch’s procedure
Under microscope, observed B. anthracis cells in blood and spleen of dead sheep
Inoculated mice with the infected sheep blood
Recovered B. anthracis from blood of mice
Grew bacteria in pure culture and showed that they caused anthrax when injected into healthy mice.
From this and later work with Mycobacterium tuberculosis, Koch’s Postulates formalized

40. Types of Immunity Naturally acquired passive
From mother at birth
Temporary
Recover from disease
Make antibodies
Permanent in most cases
Artificially acquired passive
From a serum
Some other animal makes the antibodies
Requires booster shot
Example tetanus
Artificially acquired active
From vaccine
You make the antibodies
Contains dead or weakened pathogens

41. References