1. Viruses, Viroids, and Prions

2. Are Viruses Living or Non-living?
They have some properties of life but not others
For example, viruses can be killed, even crystallized like table salt
However, they can’t maintain a constant internal state (homeostasis).

3. What are Viruses?
A virus is a non-cellular particle made up of genetic material and protein that can invade living cells.

4. Viral History

5. 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

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

7. Smallpox
Edward Jenner (1796) developed a smallpox vaccine using milder cowpox viruses
Deadly viruses are said to be virulent
Smallpox has been eradicated in the world today

8. Viewing Viruses 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

9. Size of Viruses

10. Viral Structure

11. Characteristics Non living structures Noncellular
Contain a protein coat called the capsid
Have a nucleic acid core containing DNA or RNA
Capable of reproducing only when inside a HOST cell

12. Characteristics Some viruses are enclosed in an protective envelope
CAPSID
Some viruses are enclosed in an protective envelope
Some viruses may have spikes to help attach to the host cell
Most viruses infect only SPECIFIC host cells
DNA
ENVELOPE
SPIKES

13. Characteristics
Viral capsids (coats) are made of individual protein subunits
Individual subunits are called capsomeres
CAPSOMERES

14. Characteristics Outside of host cells, viruses are inactive
Lack ribosomes and enzymes needed for metabolism
Use the raw materials and enzymes of the host cell to be able to reproduce
EBOLA VIRUS
HIV VIRUS

15. Characteristics Some viruses cause disease
Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, Ebola
Some viruses may cause some cancers like leukemia
Virus-free cells are rare
MEASLES

16. Viral Shapes Viruses come in a variety of shapes
Some may be helical shape like the Ebola virus
Some may be polyhedral shapes like the influenza virus
Others have more complex shapes like bacteriophages

17. Helical Viruses

18. Polyhedral Viruses

19. Complex Viruses

20. Taxonomy of Viruses

21. Viral Taxonomy Family names end in -viridae Genus names end in -virus
Viral species: A group of viruses sharing the same genetic information and ecological niche (host).
Common names are used for species
Subspecies are designated by a number

22. Viral Taxonomy Examples
Herpesviridae
Herpesvirus
Human herpes virus 1, HHV 2, HHV 3
Retroviridae
Lentivirus
Human Immunodeficiency Virus 1, HIV 2

23. Herpes Virus
SIMPLEX I and II

24. Adenovirus
COMMON COLD

25. Influenza Virus

26. Chickenpox Virus

27. Papillomavirus – Warts!

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

29. Bacteriophages

30. Phages
Viruses that attack bacteria are called bacteriophage or just phage
T-phages are a specific class of bacteriophages with icosahedral heads, double-stranded DNA, and tails

31. T-phages The most commonly studied T-phages are T4 and T7
They infect E. coli , an intestinal bacteria
Six small spikes at the base of a contractile tail are used to attach to the host cell
Inject viral DNA into cell

32. Escherichia Coli Bacterium
T - EVEN PHAGES ATTACK THIS BACTERIUM

33. T-Even Bacteriophages

34. Diagram of T-4 Bacteriophage
Head with 20 triangular surfaces
Capsid contains DNA
Head & tail fibers made of protein

35. Retroviruses

36. Characteristics of Retroviruses
Contain RNA, not DNA
Family Retroviridae
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

37. ENZYME

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

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

40. Viroids & Prions

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

42. 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”

43. Prion Diseases Prions form insoluble deposits in the brain
Causes neurons to rapidly degeneration.
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

44. Viral Replication

45. Viral Attack Viruses are very specific as to which species they attack
HOST specific
Humans rarely share viral diseases with other animals
Eukaryotic viruses usually have protective envelopes made from the host cell membrane

46. 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)

47. Bacteriophage Replication
Bacteriophage inject their nucleic acid
They lyse (break open) the bacterial cell when replication is finished

48. Lytic Cycle Review
Attachment Phage attaches by tail fibers to host cell
Penetration Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell
Biosynthesis Production of phage DNA and proteins
Maturation Assembly of phage particles
Release Phage lysozyme breaks cell wall

49. 1 2 3 Bacterial cell wall Bacterial chromosome Capsid DNA Capsid
Sheath
Tail fiber 1
Attachment: Phage attaches to host cell.
Tail
Base plate
Pin
Cell wall
Plasma membrane 2
Penetration: Phage pnetrates host cell and injects its DNA.
Sheath contracted
Tail core 3
Merozoites released into bloodsteam from liver may infect new red blood cells

50. 4 5 Tail DNA Maturation: Viral components are assembled into virions.
Capsid 5
Release: Host cell lyses and new virions are released.
Tail fibers

51. One-step Growth Curve
If all 500 viruses released attach to new cells, how many viruses could there be in the body at the end of the next 40 minute cycle?

52. 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 (stress, illness, etc.)
HIV, Herpes, and chickenpox (causes shingles) viruses are examples

53. Lysogenic Cycle Phage DNA injected into host cell
Viral DNA joins host DNA forming a prophage
When an activation signal occurs, the phage DNA starts replicating

54. Lysogenic Cycle Viral DNA (part of prophage) may stay
inactive in host cell
for long periods of
time
Replicated during each binary fission
Over time, many
cells form containing the prophages

55. Viral Latency
Once a prophage cell is activated, host cell enters the lytic cell
New viruses form & the cell lyses (bursts)
Virus said to be virulent (deadly)
ACTIVE STAGE
INACTIVE STAGE

56. Virulent Viruses
HOST CELL LYSES & DIES

57. The Lysogenic Cycle

58. 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

59. Latency in Eukaryotes
Herpes viruses also become 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 Simplex 1)
SKIN TO SKIN CONTACT
PASSED AT BIRTH TO BABY

60. VIRUS DESTROYING HOST CELL
Virulence
VIRUS DESTROYING HOST CELL

61. Lytic and Lysogenic Cycles

62. Body’s Defense Against Disease Causing Agents

63. First Line of Defense Skin, mucous, cilia, stomach acid, and saliva
Think of the human body as a hollow plastic tube…
The food is digested within the hole in the tube, but it never actually enters into the solid plastic material.
Tube inner surface ~Digestive System~
Tube inner surface ~Digestive System~
Tube inner surface ~Digestive System~

64. Second Line of Defense ~White Blood Cells~
If invaders actually get within the body, then your white blood cells (WBCs) begin their attack
WBCs normally circulate throughout the blood, but will enter the body’s tissues if invaders are detected

65. White Blood Cells ~Phagocytes~
These white blood cells are responsible for eating foreign particles by engulfing them
Once engulfed, the phagocyte breaks the foreign particles apart in organelles called Lysosomes

66. The Second Line of Defense ~Interferon~
Virus-infected body cells release interferon when an invasion occurs
Interferon – chemical that interferes with the ability to viruses to attack other body cells

67. White Blood Cells ~T-Cells~
T-Cells, often called “natural killer” cells, recognize infected human cells and cancer cells
T-cells will attack these infected cells, quickly kill them, and then continue to search for more cells to kill

68. The Second Line of Defense ~The Inflammatory Response~
Injured body cells release chemicals called histamines, which begin inflammatory response
Capillaries dilate
Pyrogens released, reach hypothalamus, and temperature rises
Pain receptors activate
WBCs flock to infected area like sharks to blood

69. Two Divisions of the Immune System
The efforts of the WBCs known as phagocytes and T-cells is called the cell-mediated immune system.
Protective factor = living cells
Phagocytes – eat invaders
T-cells – kill invaders

70. Two Divisions of the Immune System
The other half of the immune system is called antibody-mediated immunity, meaning it is controlled by antibodies
This represents the third line of defense in the immune system

71. The Third Line of Defense ~Antibodies~
Most infections never make it past the first and second levels of defense
Those that do trigger the production and release of antibodies
Proteins that latch onto, damage, clump, and slow foreign particles
Each antibody binds only to one specific binding site, known as an antigen

72. Antibody Production
WBCs gobble up invading particles and break them up
They show the particle pieces to T-cells, who identify the pieces and find specific B-cells to help
B-cells produce antibodies that are equipped to find that specific piece on a new particle and attach

73. What is immunity?
Resistance to a disease causing organism or harmful substance
Two types
Active Immunity
Passive Immunity

74. Immunity
New particles take longer to identify, and a person remains ill until a new antibody can be crafted
Old particles are quickly recognized, and a person may never become ill from that invader again. This person is now immune.

76. Active Immunity You produce the antibodies
Your body has been exposed to the antigen in the past either through:
Exposure to the actual disease causing antigen – You fought it, you won, you remember it
Planned exposure to a form of the antigen that has been killed or weakened – You detected it, eliminated it, and remember it

77. Vaccines An attenuated virus is a weakened, less vigorous virus
“Attenuate" refers to procedures that weaken an agent of disease (heating)
A vaccine against a viral disease can be made from an attenuated, less virulent strain of the virus
Attenuated virus is capable of stimulating an immune response and creating immunity, but not causing illness

78. Vaccine
Antigens are deliberately introduced into the immune system to produce immunity
Because the bacteria has been killed or weakened, minimal symptoms occur
Have eradicated or severely limited several diseases from the face of the Earth, such as polio and smallpox

79. How long does active immunity last?
It depends on the antigen
Some disease-causing agents multiply into new forms that our body doesn’t recognize, requiring annual vaccinations, like the flu shot
Booster shot - reminds the immune system of the antigen
Others last for a lifetime, such as chicken pox

80. Think the flu is no big deal?
Think again…
In 1918, a particularly deadly strain of flu, called the Spanish Influenza, spread across the globe
It infected 20% of the human population and killed 5%, which came out to be about 100 million people

81. Do we get all the possible vaccines we can?
Although the Center for Disease Control (CDC) recommends certain vaccines, many individuals go without them
Those especially susceptible include travelers and students
Consider the vaccine for meningitis, which is recommended for all college students and infects 3,000 people in the U.S., killing 300 annually

82. Passive Immunity You don’t produce the antibodies
A mother will pass immunities on to her baby during pregnancy - through what organ?
These antibodies will protect the baby for a short period of time following birth while its immune system develops. What endocrine gland is responsible for this?
Lasts until antibodies die
Thymus
Placenta
Why doesn’t the mother just pass on the WBCs that “remember” the antigens?

83. Acquired Immune Deficiency Syndrome
Caused by the Human Immunodeficiency Virus
Discovered in 1983
Specifically targets and kills T-cells
Because normal body cells are unaffected, immune response is not launched

84. AIDS ~The Modern Plague~
The HIV virus doesn’t kill you – it cripples your immune system
With your immune system shut down, common diseases that your immune system normally could defeat become life-threatening
Can show no effects for several months all the way up to 10 years

85. AIDS ~The Silent Spread~
Transmitted by sexual contact, blood transfusions, contaminated needles
As of 2007, it affects an estimated 33.2 million people

86. Other Viral Treatments
Interferon are naturally occurring proteins made by cells to fight viruses
Genetic altering of viruses (attenuated viruses)
Antiviral drugs (AZT)
Protease inhibitors – prevent capsid formation