KEY CONCEPT Infections can be caused in several ways.

1. KEY CONCEPTInfections can be caused in several ways.

2. Discovery of Viruses • Beijerinck (1897) coined the Latin name “virus” meaning poison • He studied filtered plant juices & found they caused healthy plants to become sick

3. Tobacco Mosaic Virus • Wendell Stanley (1935) crystallized sap from sick tobacco plants • He discovered viruses were made of nucleic acid and protein

4. Smallpox • Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses • Deadly viruses are said to be - virulent • Smallpox had been eradicated in the world today, but is now coming back

5. Viruses are smaller than the smallest cell • Measured in nanometers • Viruses couldn’t be seen until the electron microscope was invented in the 20th century

6. Size of Viruses

7. Viruses, bacteria, viroids, and prions can all cause infection. • Any disease-causing agent is called a pathogen. 1 nanometer (nm) = one billionth of a meter 100 nm eukaryotics cells10,000-100,000 nm viroids5-150 nm viruses50-200 nm prokaryotics cells200-10,000 nm prion2-10 nm

8. A virus is made of DNA or RNA and a protein coat. • non-living pathogen • can infect many organisms • A viroid is made only of single-stranded RNA. • causes disease in plants • passed through seeds or pollen

9. Viroids • Small, circular RNA molecules without a protein coat • Infect plants • Potato famine in Ireland • Resemble introns

10. causes misfolding of other proteins • results in diseases of the brain • A prion is made only of proteins.

11. 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”

12. Prion Diseases • Causes neurons to rapidly degenerate. • Examples: • Mad cow disease (bovine spongiform encephalitis: BSE) • People in New Guinea used to suffer from kuru, which they got from eating the brains of their enemies

13. Clicker QuestionPrions can be contracted by… A: Eating leftovers from the fridge. B: Eating the brain of an infected animal. C: Eating meat that has come into contact with the brain or spinal cord of an infected animal. D: Both B and C

14. What infectious element causes Mad Cow Disease? A: Phages B: Prions C: Viroids D: Plasma E: Virus Clicker Question!

15. KEY CONCEPT Viruses exist in a variety of shapes and sizes.

16. capsid surfaceproteins nucleic acid nucleic acid capsid Surface proteins lipidenvelope capsid nucleic acid surfaceproteins lipid envelope Viruses differ in shape and in ways of entering host cells. • Viruses have a simple structure. • genetic material • capsid, a protein shell • maybe a lipid envelope, a protective outer coat enveloped(influenza) helical(rabies) polyhedral(foot-and-mouth disease)

17. Viral Characteristics • Noncellular • Have a protein coat called the capsid • Have a nucleic acid core containing DNA or RNA • Capable of reproducing only when inside a HOST cell

18. Characteristics • Some viruses are enclosed in a protective envelope • Some viruses may have spikesto help attach to the host cell • Most viruses infect only SPECIFIC host cells CAPSID DNA ENVELOPE SPIKES

19. Helical Viruses

20. Polyhedral Viruses

21. Complex Viruses

22. Used for Virus Identification • RNA or DNA Virus • Do or do NOT have an envelope • Capsid shape • HOST they infect

23. capsid DNA tail sheath tail fiber • Bacteriophages infect bacteria.

24. colored SEM; magnifications: large photo 25,000; inset 38,000x • bacteriophages pierce host cells • Viruses enter cells in various ways.

26. Clicker Question - Phages • A Bacteriophage or a phage is: A virus that infects a __________ cell. • Plant • Animal • Bacteria • Protista • Fungi

27. Viruses enter cells in various ways. • viruses of eukaryotes enter by endocytosis

28. Viruses enter cells in various ways. • viruses of eukaryotes also fuse with membrane

29. host bacterium The bacterophage attachesand injects it DNA into a host bacterium. The host bacterium breaks apart, or lyses. Bacteriophages are ableto infect new host cells. The viral DNA forms a circle. The viral DNA directs the hostcell to produce new viral parts.The parts assemble into newbacteriophages. The virus may enter the lysogenic cycle, in which the host cell is not destroyed. Viruses cause two types of infections. • A lytic infection causes the host cell to burst.

30. 5 Steps of Lytic Cycle • 1. Attachment to the cell • 2. Penetration (injection) of viral DNA or RNA • 3. Replication (Biosynthesis) of new viral proteins and nucleic acids • 4. Assembly (Maturation) of the new viruses • 5. Release of the new viruses into the environment (cell lyses)

31. One-step Growth Curve

32. The prophage may leave the host’s DNA and enter the lytic cycle. The viral DNA is called a prophage when it combines with the host cell’s DNA. Although the prophage is not active, it replicates along with the host cell’s DNA. Many cell divisions produce a colony of bacteria infected with prophage. • A lysogenic infection does no immediate harm.

33. The Lysogenic Cycle

34. Viral Latency • Some viruses have the ability to become dormant inside the cell • Called latent viruses • They may remain inactive for long periods of time (years) • Later, they activate to produce new viruses in response to some external signal • HIV and Herpes viruses are examples

35. Latency in Eukaryotes • Some eukaryotic viruses remain dormant for many years in the nervous system tissues • Chickenpox (caused by the virus Varicella zoster) is a childhood infection • It can reappear later in life as shingles, a painful itching rash limited to small areas of the body SHINGLES

36. Latency in Eukaryotes • Herpes viruses also becomes latent in the nervous system • A herpes infection lasts for a person’s lifetime • Genital herpes (Herpes Simplex 2) • Cold sores or fever blisters (Herpes Simplex1) SKIN TO SKIN CONTACT PASSED AT BIRTH TO BABY

37. Clicker Question! • Viruses replicate: A. On their own B. With other viruses by joining pili C. When ever they want to D. In a host cell only

38. Clicker Question! • All Viruses ONLY contain RNA. A. True B. False

39. Retroviruses

40. Characteristics of Retroviruses • Contain RNA, not DNA • Contain enzyme called Reverse Transcriptase • When a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell

41. ENZYME

42. Retroviruses • The enzyme reverse transcriptase (or RTase), which causes synthesis of a complementary DNA molecule (cDNA) using virus RNA as a template RTase

43. Retroviruses • HIV, the AIDS virus, is a retrovirus • Feline Leukemia Virus is also a retrovirus

44. Clicker Question! • Retroviruses contain: A. tRNA B. DNA C. RNA D. rRNA E. mRNA

45. KEY CONCEPT Some viral diseases can be prevented with vaccines.

46. Viruses cause many infectious diseases • There are many examples of viral infections. • common cold

47. Viruses cause many infectious diseases • influenza • There are many examples of viral infections. • common cold

48. Viruses cause many infectious diseases • influenza • There are many examples of viral infections. • common cold • SARS

49. HIV-infected white blood cell Viruses cause many infectious diseases • HIV • There are many examples of viral infections. • The body has natural defenses against viruses.

50. Characteristics • Some viruses cause disease such as: • Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola • Some viruses may cause some cancers like leukemia MEASLES