Chapter 18

 1796 – Edward Jenner developed the smallpox vaccine  1897 – Beijerinck coined the term “virus” meaning poison  1935 – Wendell Stanley crystalized sap from tobacco leaves with TMV and found that viruses were made of nucleic acid and protein

 Study of viruses  Deadly viruses are virulent  Viruses couldn’t be seen until the electron microscope was invented

 Non-living ◦ Non-cellular ◦ Cannot grow or reproduce on its own ◦ No metabolism  Cause disease ◦ AIDS, colds, flu, measles, mono  Cause cancer ◦ Cervical, leukemia

 Genetic material ◦ DNA or RNA  Capsid ◦ Protein coat surrounding nucleic acid  Envelope ◦ Some; comes from host cell membrane  Mode of entry ◦ Spikes, receptors, etc.

 Host range: ◦ Broad: West Nile  Mosquitoes, birds, humans, horses ◦ Narrow: Measles  Humans  Viruses are small

 Among the most complex viruses  Attack bacterial cells  Composed of a 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

 Viral replication that rapidly kills the host cell causing it to lyse or burst  Involves 5 steps 1. Adsorption --- phage attaches to cell membrane of host 2. Injection --- nucleic acid (DNA) of virus injected into host cell 3. Replication --- viral DNA inactivates host cell's DNA & uses host's raw materials & ribosomes to make viral DNA, capsids, tails, etc. 4. Assembly --- new viral parts are combined to make new phages 5. Lysis --- enzymes weaken & destroy the cell membrane causing it to lyse releasing new viruses that infect other cells

1. Bacteriophage infects bacteria cell and injects its DNA 2. DNA becomes incorporated into bacterial chromosome ◦ Prophage 3. Bacteria reproduces, making more copies of viral DNA  Lytic cycle can be triggered

Two key variables in classifying viruses that infect animals: ◦ DNA or RNA? ◦ Single-stranded or double-stranded?

Class/FamilyEnvelopeExamples/Disease I. Double-stranded DNA (dsDNA) AdenovirusNo Respiratory diseases, animal tumors PapovavirusNo Papillomavirus (warts, cervical cancer): polyomavirus (animal tumors) HerpesvirusYes Herpes simplex I and II (cold sores, genital sores); varicella zoster (shingles, chicken pox); Epstein-Barr virus (mononucleosis, Burkitt’s lymphoma) PoxvirusYes Smallpox virus, cowpox virus

Class/FamilyEnvelopeExamples/Disease II. Single-stranded DNA (ssDNA) ParvovirusNoB19 parvovirus (mild rash) III. Double-stranded RNA (dsRNA) ReovirusNoRotavirus (diarrhea), Colorado tick fever virus

Class/FamilyEnvelopeExamples/Disease IV. Single-stranded RNA (ssRNA); serves as mRNA PicornavirusNoRhinovirus (common cold); poliovirus, hepatitis A virus, and other enteric (intestinal) viruses CoronavirusYesSevere acute respiratory syndrome (SARS) FlavivirusYesYellow fever virus, West Nile virus, hepatitis C virus TogavirusYesRubella virus, equine encephalitis viruses

Class/FamilyEnvelopeExamples/Disease V. ssRNA; template for mRNA synthesis FilovirusYes Ebola virus (hemorrhagic fever) OrthomyxovirusYes Influenza virus ParamyxovirusYes Measles virus; mumps virus RhabdovirusYes Rabies virus VI. ssRNA; template for DNA synthesis RetrovirusYes HIV (AIDS); RNA tumor viruses (leukemia)

 Contain RNA  Reverse transcriptase enzyme uses the RNA to make DNA  Use the host cell's ribosomes & raw materials to make viral proteins  Cause some cancers & AIDS

 Smallest particle able to replicate  Made of a short, single strand of RNA with no capsid  Cause disease in plants

 Infectious protein ◦ protein particles that have folded incorrectly  No nucleic acid or capsids  Attacks the central nervous system  Cause animal diseases in cows (Mad Cow disease), sheep, & humans

 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