1. Viruses!

2. Check Your Prior Knowledge
True or False: Viruses are larger than bacteria.

3. Check Your Prior Knowledge
True or False: Viruses can only infect animals.
False, viruses can infect organisms of any kingdom.

4. Check Your Prior Knowledge
True or False: Viruses are responsible for all diseases.

5. Size Matters
Recall that bacteria are prokaryotes with cells much smaller and more simply organized than those of eukaryotes.
Viruses are smaller and simpler still.
0.25 m
Animal cell nucleus
Virus
Bacterium
Animal cell

6. The Hunt For Virus?
Scientists were able to detect viruses indirectly long before they were actually able to see them.

7. The Discovery of Viruses
Tobacco mosaic disease stunts the growth of tobacco plants and gives their leaves a mosaic coloration.
It was discovered in 1930 by Wendell M. Stanley.
A Nobel Prize was won in 1946 for this discovery!

8. What is the definition of Living?
To be considered alive, an organism must:
Be made of at least one cell.
Be able to grow and reproduce independently.
Have information stored in DNA.
The big question:
Do viruses fulfill these criteria?

9. The Big Questions Do viruses fulfill these criteria?
Are viruses made of at least one cell?

10. What Is A Virus? VIRUSES ARE NOT CELLS!!! Virus Bacterium Animal cell
Animal cell nucleus

11. Viral Structure
Viruses are very small infectious particles consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope.

12. Viral Structure
At the most basic level, viruses can be classified as segments of nucleic acids contained in a protein coat.

13. Varicella zoster (the chicken pox virus) has a DNA genome.
Parts Of A Virus
The nucleic acid found in a virus can be either RNA or DNA, but cannot be both.
Varicella zoster (the chicken pox virus) has a DNA genome.
HIV has an RNA genome.

14. (a) Tobacco mosaic virus
Parts Of A Virus
A capsid is the protein coat that encloses the viral genome and can have various structures.
(a) Tobacco mosaic virus
(b) Adenoviruses
RNA
DNA
Capsid
Glycoprotein

15. Parts Of A Virus
Some viruses have an envelope that surrounds the capsid and helps the virus enter cells.
It is derived from the host’s cell membrane and includes glycoproteins.

16. Virus Shapes
Viruses exist in many shapes.
Thread-like - Ebola.

17. Virus Shapes
Viruses exist in many shapes.
Spherical - Influenza.

18. Virus Shapes Viruses exist in many shapes.
Rods - Tobacco Mosaic Virus.

19. Virus Shapes
Viruses exist in many shapes.
Polyhedral - Adenovirus.

20. Virus Shapes Viruses exist in many shapes.
Hard to classify shape  - Bacteriophage.

21. The Big Questions Do viruses fulfill these criteria?
Are viruses made of at least one cell?

22. The Big Questions Do viruses fulfill these criteria?
Are viruses able to grow and reproduce independently?

23. Viral Replication
In short, viruses can reproduce ONLY by infecting living cells.

24. Two Methods of Viral Reproduction
Lytic Cycle
Lysogenic Cycle

25. The Lytic Cycle
The lytic cycle is a reproductive cycle that culminates in the death of the host.
The virus produces new viruses and digests the host’s cell wall, releasing the progeny viruses.

26. Lytic Cycle

27. Lytic Cycle 1 2 5 4 3 Attachment Entry of viral DNA Release
Synthesis of viral DNA and proteins 3
Assembly of viruses 4
Release 5
Entry of viral DNA 2

28. The Lysogenic Cycle
The lysogenic cycle replicates the viral genome without destroying the host.
The viral DNA is replicated, but new viruses are not made during the lysogenic cycle.
New viruses are only made during the lytic cycle!
A virus in the lysogenic cycle may come out of dormancy and enter the lytic cycle.

29. The Lysogenic Cycle

32. The Lysogenic Cycle
???
What is this

33. What Is A Provirus?
After the viral nucleic acid is inserted into the cell, it may be integrated into the cell’s DNA.
When the viral DNA are integrated into the cell’s DNA, it is known as a provirus.

34. The Lysogenic Cycle
The red part of the circle is the provirus.

35. The Big Questions Do viruses fulfill these criteria?
Are viruses able to grow and reproduce independently?

36. The Big Questions Do viruses fulfill these criteria?
Do viruses have information stored in DNA?

37. Let’s Review: Parts Of A Virus
Nucleic acid (RNA or DNA), capsid and envelopes on some viruses.
Varicella zoster (the chicken pox virus) has a DNA genome.
HIV has an RNA genome.

38. Retroviruses
Some viruses, such as HIV, have RNA as their genetic material instead of DNA.
HIV is known as a retrovirus. Retroviruses work very differently than other viruses.

39. Retroviruses
Retroviruses replicate their nucleic acids in reverse using an enzyme called reverse transcriptase.
This enzyme that allows them to transcribe RNA to DNA, instead of DNA to RNA like normal.

40. Retroviruses
The newly transcribed DNA is then integrated into the host’s DNA as a provirus!
Viral RNA is reverse transcribed into DNA. 2
Viral DNA is integrated into the host cell’s DNA, creating a provirus. 3
Viral RNA enters the host cell. 1
Host cell replicates the viral DNA (lysogenic cycle). 4

41. The Big Questions Do viruses fulfill these criteria?
Do viruses have information stored in DNA?

42. So……Are Viruses Living?
To be considered alive, an organism must:
Be made of at least one cell.
Viruses are not made of cells.
Be able to grow and reproduce independently.
Viruses do not grow and reproduce independently.
Have information stored in DNA.
Viruses have information stored in DNA or RNA.

43. Are Viruses Living?
No!!!!
Viruses are not considered alive because they are not made of cells and they do not grow or reproduce on their own.

44. Pathogens A pathogen is anything that can cause you harm.
Viruses are pathogens, or agents that cause disease.
Viruses can cause disease in all living things including in bacteria, fungi, protists, plants and animals.
Because they cause disease, viruses have a major impact on the living world.

45. Viral Diseases AIDS - Acquired Immunodeficiency Syndrome
Caused by Human Immunodeficiency Virus.
transmitted through direct contact of a mucous membrane or bloodstream with blood, semen, vaginal fluid, pre-seminal fluid, and breast milk.
The virus kills the Helper T Cells of the immune system.

46. Viral Diseases AIDS - Acquired Immunodeficiency Syndrome
Caused by Human Immunodeficiency Virus.
HIV can be transmitted by:
All types of sex.
Dirty needles.
Blood
Mother to child during pregnancy and/or childbirth.
Breastfeeding.

47. Viral Diseases AIDS - Acquired Immunodeficiency Syndrome
Caused by Human Immunodeficiency Virus.
There is no cure or preventative vaccine available.

48. Viral Diseases Common Cold Symptoms
Sinus congestion, muscle aches, cough, fever and sore throat.
Transmitted by inhalation or direct contact.

49. Viral Diseases Ebola Symptoms High fever and uncontrollable bleeding.
Transmitted through bodily fluids.

50. Viral Diseases Influenza (flu) Symptoms
Fever, chills, fatigue, cough, sore throat, muscle aches, weakness and headache.
Transmitted by inhalation.

51. Viral Diseases Mumps Symptoms Painful swelling in salivary glands.
Transmitted by inhalation.

52. Viral Diseases Polio Symptoms
Fever, headache, stiff neck and possible paralysis.
Transmitted by fecally contaminated food or water.

53. Viral Diseases Rabies Symptoms
Mental depression, fever, restlessness, difficulty swallowing, paralysis and convulsions. It can be fatal.
Transmitted by the bite of an infected animal.

54. Viral Diseases Smallpox Symptoms
Blisters, lesions, fever, malaise, blindness and disfiguring scars. It was often fatal.
Transmitted by inhalation.
Eradicated in 1979.

55. Viral Diseases Chicken pox (varicella- zoster virus) Symptoms
A fever, feeling sick, tired, and sluggish, little or no appetite, headache, sore throat and itchy rash.
Transmitted through the air via a cough or sneeze.

56. What are Vaccines?
Vaccines are a weakened or killed form of the virus.
By injecting this into the body, your body will build antibodies towards this particular virus.

57. What are Vaccines?
When your body is infected with the real virus, you already have the antibodies to fight it
Vaccines are used for prevention only! They cannot do anything to fight a virus if you are already infected.

58. Special Types of Viruses And Their Relatives

59. Viruses That Only Infect Bacteria
A bacteriophage is a special type of virus that only infects bacteria.
The T4 bacteriophage is an example.

60. Prions
Prions are pathogenic, virus-like particles made up completely of misfolded proteins.
They are not made up of DNA or RNA.

61. Prions
Example
Mad Cow Disease (bovine spongiform encephalopathy)
Most prions affect the structure of the brain or other neural tissue, and all are currently untreatable and are always fatal.

62. Potato Spindle Tuber Viroid
Viroids
A viroid is a plant pathogen that consists of a short stretch of RNA.
Potato Spindle Tuber Viroid

63. Viroids
A viroid is a plant pathogen that consists of a short stretch of RNA.

64. Put It All Together!
Write down 3 things you have learned about viruses.