1. Viruses  A virus is not a cell. It lives only within a living cell and has no attributes of a living organism.  It is an obligate intracellular parasite.

2. Viruses  A virus is not a cell. It lives only within a living cell and has no attributes of a living organism.  It is an obligate intracellular parasite. Review! What does obligate mean? Capable of functioning or surviving only in a particular condition What is a parasite? Organism that lives and derives nourishment at the detriment of the host What is an obligate parasite?

3. Viruses  It is made up of DNA or RNA inside a protein coat called a capsid. RNA

4. Virus  Some take lipids from the cell it infects and make a covering over the capsid that has glycoprotein receptors.  Receptors are used to attach to the host’s membrane. RNA

5. Virus Structure

6. Viruses  A virus is not a cell  It is made up of genetic material inside a protein coat  Viruses do not carry on most metabolic activities

7. Viruses  Viruses that attack only bacteria are known as bacteriophages.

8. Virus Reproduction – Lytic Cycle

9.  AttachmentPhage attaches by tail fibers to host cell  PenetrationPhage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell  BiosynthesisProduction of phage DNA and proteins  MaturationAssembly of phage particles  ReleasePhage lysozyme breaks cell wall Multiplication of Bacteriophages (Lytic Cycle)

10. Virus Reproduction – Lysogenic Cycle

11. Lytic or Lysogenic Cycle? The animation on the next slide demonstrates which cycle?

13. Lytic vs Lysogenic  Lytic cycle –Phage causes lysis and death of host cell  Lysogenic cycle –Prophage DNA incorporated in host DNA

14. Virus Classification

15. Smallpox   Although smallpox was declared extinct in the wild in 1979 (last natural infection recorded in 1977) there is increasing concern about its potential use as a biological weapon. Although only two locations officially hold variola (one at the CDC in the USA and one in Russia) it is feared that secret stockpiles exist.

16. Smallpox   CLASSIFICATION OF THE SMALLPOX VIRUS   GENOME: Linear Double Stranded DNA   Family: Poxviridae   Subfamily: Chordopoxvirinae   Genus: Orthopoxvirus   Species: Variola

17. Prions and Viroids Bits and Pieces that cause disease

18. 18 Viroids  Small, circular RNA molecules without a protein coat  Infect plants  Potato famine in Ireland  Resemble introns cut out of eukaryotic copyright cmassengale

19. 19 Prions  Prions are “infectious proteins”  They are normal body proteins that get converted into an alternate configuration by contact with other prion proteins  They have no DNA or RNA  The main protein involved in human and mammalian prion diseases is called “PrP” copyright cmassengale

20. 20 Prion Diseases  Prions form insoluble deposits in the brain  Causes neurons to rapidly degenerate.  Mad cow disease (bovine spongiform encephalitis: BSE) is an example  People in New Guinea used to suffer from kuru, which they got from eating the brains of their enemies copyright cmassengale

21. Virus Reproduction

22. Negative Virus Influences  They cause infections in both plants and animals  Some viruses cause tumors and warts  They also destroy cells and are responsible for human diseases such as –polio –measles –mumps –influenza –hepatitis –colds –AIDS

23. Human Papilloma Virus - Warts Influenza Virus - Flu Human Immunodeficiency Virus AIDS Rabies Virus

24. Positive Virus Influences  Certain viruses are used in the control of insect pests  Others are used in genetic research  Scientists have been able to use viruses to biologically control caterpillars of the European pine sawfly and the gypsy moth