Viruses

1. Living or Non-living? Viruses

2. Viruses • Viruses are the smallest organisms in biology; however, the debate is still on whether to classify them as living. • What makes something living or non-living? • Are viruses living?

3. Are Viruses Living? Living Characteristics: • contain DNA or RNA • have protein ( therefore Carbon) • contain small amounts of enzymes

4. Are Viruses Living? Non Living Characteristics • Non cellular • Do not respire (breathe), respond to stimuli, or “grow” • Reproduce only within living cells, and are assembled in parts which join together.

5. Cell Theory by Schleiden & Schwann • All living things are composed of cells • The cell is the basic living unit of organization • All cells arise from pre-existing cells • Cells do not come from nonlivingthings

6. What is a Virus? • A virus is a noncellular particle made up of genetic material and protein that can invade living cells • Viruses use the living host cells to reproduce their viral DNA • Viruses are considered to be nonliving

7. Examples

8. History Small Pox • Prior to the 1700s this disease meant certain death • Edward Jennerobserved that milkmaids would survive this disease • Jenner Hypothesized that cow pox provided protection • Proved this by injecting his own son and named this technique vaccination (Latin for “pertaining to the cow)

9. Discovery of Viruses • First identified was the tobacco mosaic viruses • Adolf Meyer (1883) - discovered the disease could be spread via juice from an infected plant. • Dmitri Ivanowski (1893)- Passed sap through bacteria filters – small bacteria or chemical toxin?

10. Discovery of Viruses • Martinus Beijerinick (1890s)- Diluted filtered sap and found it was still toxic • Concluded that a extremely small pathogen was at work (virus = dutch for poison) • Wendell Stanley (1930s) -Used the electron microscope to identify TMV

11. Viral Diversity • Viruses come in many shapes and sizes • Viruses are much too small to be seen with any light microscope.  • The smallpox virus is more than 5 times smaller than the bacterium E. coli

12. Sizes

13. Shapes

14. Structure of a Virus A typical virus is composed of: • Nucleic Acid (DNA) • Capsid (protein coat to protect DNA) • BacteriophageT4 is a complex virus with a tail and tail fibers

15. Bacteriophage Structure A DNA Head Capsid B C Tail Fibers Tail

16. Electron Microscope

17. VIRUSES Life Cycle

18. Viral Life Cycles There are two cycles for viral reproduction: • Lytic Cycle • Lysogenic Cycle • These two cycles should not be seen as separate, but rather interchangeable.

19. Lytic Cycle • This type of viral infection follows the pattern of infection, replication, and lysis. • Viral infection can spread quickly in a multicellular organism as the lytic cycle is repeated over and over again destroying hundreds of host cells at an exponential rate in a matter of hours. • Viruses that produce a lytic cycle are said to be virulent.

20. Lytic Cycle A Infection C B Lysis Replication & Assembly

21. Lytic Cycle Part A: Infection • virus attaches to specific cell  cell specificity Part B: Replication & Assembly • cell is opened by enzymes • virus DNA or RNA enters into the cell, remaining structures stay outside.

22. Lytic Cycle Part B Continued • virus DNA is inserted into host DNA causing the replication of more virus DNA and parts. • Virus parts and DNA are assembled Part C: Lysis • Viruses burst out of the host cell lysis • 1 virus in  up to 300 viruses out! • Host cell is destroyed

23. Lysogenic Cycle • In this pattern of infection, the viral DNA is incorporated into the host cell’s chromosome and remains dormant while it is mass-produced as the host cell divides. • A virus that exists in the cell but does not lyse out of the cell is called latent. • The latent period can last for years. Ex: HIV latent period can be 10-25 years.

24. Lysogenic Cycle • When conditions trigger activation of the viral chromosome, replication and lysis follow the lytic cycle. • Activation of dormant viruses can be caused by UV radiation, stress, temperature, nutrients, etc

25. Lysogenic Cycle Viral DNA inserted A Lysis Infection B Reproduction of host cells (virus dormant) G C F E Assembly D Activation Replication

26. Interchangeable Viral Cycles

27. Retroviruses • Some viruses contain RNA instead of DNA • A retrovirus assembles its code into the host cell’s DNA • HIV is a retrovirus • Cancer causing viruses are also retroviruses

28. Review What cycle is this? What evidence do you see?

29. Review B: What cycle is this? A: What cycle is this?

30. Group Activity • In groups of 5-6, you will demonstrate your knowledge of the lysogenic cycle in one of the following creative formats: • Skit • News Broadcast • Rap • Other?

31. Group Activity • Your presentation must be ~ 5 minutes long • You must include the following:

32. Review: A DNA Head Capsid B C Tail Fibers Tail

33. Review A Infection C B Lysis Replication & Assembly

34. Review Viral DNA inserted A Lysis Infection B Reproduction of host cells (virus dormant) G C F E Assembly D Activation Replication

35. Defense against VIRUSES Our Immune System

36. Our Immune System: • is the most complex system in our body • is our primary defense against infection from pathogens • effectively responds to antigens (foreign substances on pathogens like viruses & bacteria) in a number of different ways

37. Our Immune System •  is controlled by our white blood cells: • Phagocytes = white blood cells that engulf and destroy antigens • Lymphocytes = B and T Cells

38. White Blood Cells B – Lymphocytes (B-cells) • mature in our bone marrow and make antibodies

39. Antibodies • Antibodies are special proteins that bind to specific antigens on the surface of a pathogen and help destroy it by poking holes in its structure.

40. White Blood Cells T - Lymphocytes : • function by identifying & presenting the antigen to the B – cells to activate antibody production. • Low T - Cell counts are implicated in cancers.

41. Immunity • The production of antibodies from the first exposure to an antigen is called the primary immune response • Once the body has been exposed to an antigen, a large number of B and T- Cells (memory cells) remain capable of producing a more powerful and faster secondary immune response to the same antigen

42. Immunity There are different types of immunity: • Innate  born with it • Acquired  achieved in four ways:

43. Acquired Immunity

44. Acquired Immunity

45. Acquired Immunity

46. Acquired Immunity

47. Questions Page 976 • What is an antigen? Why are antigens important to the immune system? • What are the two main types of lymphocytes? What roles do they play in the immune system? • Compare and contrast active and passive immunity. Give examples of each. • Do you think vaccines are good for children? Why or why not?

48. Defense against VIRUSES Part II: Immune System

49. Our Immune System: • Consists of specific and nonspecific defenses against infection • Nonspecificdefenses are the body’s primary line of defense against all pathogens • Specific defensemechanisms involve the production of antibodies against particular pathogens (discussed last class)

50. Nonspecific Defenses • Nonspecific defenses provide physical and chemical barriers against infection • Non-specific defense mechanisms can be divided into first-line and second-line defenses