1. Viruses Characteristics, Structures, Types, and Replication

2. Virus Characteristics (almost) Smallest biological particles May only exist by infecting host cells

3. Are viruses alive? YES NO

4. Virus Characteristics continued Viruses are considered nonliving –Some, but not all characteristics of life

5. Viral Structure All viruses have two parts –a nucleic acid core –a protein coat called a capsid.

6. Parts of a generic virus bacteriophage

7. Viral Structure envelope Viruses without an envelope are known as naked viruses

8. What extra structures does this have? Virus Structure

9. Viral Classification 1. By the type of nucleic acid 2. By what type of outer covering they have

10. Examples of virus shapes. What makes these viruses different?

11. 3. By the shape of the virus Determined by its capsid icosahedral helical

12. Viral Classification (continued) 4. by who they infect Host Cell Specificity Very specific--Three levels 1. 2. 3.

13. Viral Classification 5. By how they infect DNA (2 ways), RNA, Retroviruses

14. Viral Types DNA viruses –(goes) to RNA –joins with host’s DNA RNA viruses –(goes) straight to protein with use of host’s ribosomes (in the cytoplasm) Retroviruses –use enzyme reverse transcriptase converts viral RNA to DNA and new DNA can become part of host DNA or go to RNA DNA →RNA RNA →DNA→RNA DNA→ integrated DNA→RNA

15. Life cycle of a virus Process of virus replication 1.Lysogenic Cycle 2.Lytic cycle

16. LYSOGENIC CYCLE Lysogenic cycle – incorporates DNA into host’s 1.Attach 2.inject DNA 3.Incorporate DNA into host cell’s chromosome (prophage) 4.Replicate as host cell replicates 5.At some point may disattach and complete the lytic cycle

17. Viral Replication 1. Attachment Virus comes in contact with receptor sites on surface of host cell (specific host cell) Virus attaches to cell

18. Viral Replication 2. Inject DNA Inject DNA –Naked virus injects nucleic acid into host or –Enveloped viruses join with cell membrane

19. Viral Replication 3. Replication –Viral DNA (or RNA) directs protein synthesis –Viral nucleic acid causes host cell to produce parts of virus

20. Viral Replication 4. Assembly Nucleic acid are inserted into capsid New viruses are ready to be released

21. Viral Reproduction 5. Release Host cell membrane breaks down Viruses are released LYTIC CYCLE

22. Viral Reproduction Release Enveloped viruses move through cell membrane, taking some of the cell’s membrane with it

23. Major viral disease treatment factoids: No viral disease has ever been CURED by medical treatment. Viruses are not susceptible to ANTIBIOTICS. If a doctor tells you he/she is treating your VIRUS INFECTION with an antibiotic, he/she is either stupid or lying and you should seek more competent medical advice. The most effective tool is prevention (immunization)

24. First Vaccination On 14th May 1796, Edward Jenner used cowpox- infected material obtained from the hand of Sarah Nemes, a milkmaid from his home village of Berkley in Gloucestershire to successfully vaccinate 8 year old James Phipps. On 1st July 1796, Jenner challenged the boy by deliberately inoculating him with material from a real case of smallpox ! He did not become infected !