1. Viruses
Chapter 18

2. VIRUS: Latin word for poison
Virus: Non-living,
parasitic, biological
particle.
All viruses cause some sort of disease. Some even cause cancer.

3. VIRUSES do not “live” because:
They can not reproduce outside a “host” cell
They do not carry out cellular respiration
They do not grow or develop

4. Virus structure DNA or RNA Core Capsid
Holds the genetic material that will affect the host
Capsid
Outer protein coat that enables the virus to enter certain cells.

5. Virus structure Glycoproteins
Projections that help the virus attach to host
Not all viruses have glycoproteins.

6. Virus Size
Viruses are smaller than the smallest cell

7. Virus Vocab Host: a cell in which a virus replicates
Host Specific: most viruses or bacteria will only affect a single host or a small group of host species
Examples:
West Nile Virus – affects birds, horses, and people
Influenza type B – affects only people not others
Parvo – affects only dogs, not other organisms

8. Types of Viruses

9. Bacteriophages

10. 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

11. 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

12. Viruses Blow Up the Cell the Affect!!!
Once the viral genes get inside a cell, the genes are expressed.
This genetic program causes the host cell to make copies of the virus.
In the process, the host cell is destroyed.

13. Viruses Blow Up the Cell they Affect!!!
There are two ways this can occur
The Lytic Cycle
The Lysogenic Cycle

14. The Lytic Cycle Lysis – to break or rupture cells or cell membranes
STEPS
Attach
Virus “docks” with host cell
Injection
Virus inject it’s DNA/RNA into host cell
Replicate
replication of virus parts
Lysis
cell ruptures and new virus’ invade tissues of the host
Lysis – to break or rupture cells or cell membranes

15. The Lysogenic Cycle STEPS Attach Virus “docks” with host cell
Injection
Virus inject it’s DNA/RNA into host cell
Incorporate
DNA attaches to the cells own DNA
Time Goes By
Stress
Replicate
replication of virus parts
Lysis
cell ruptures and new virus’ invade tissues of the host

16. Examples of Lytic Viral Infections
1. Common Cold
How do we catch it?
Contact with contaminated objects; droplet inhalation
What are the symptoms?
Sneezing, Sore Throat, Fever, Headache, Muscle Aches

17. Examples of Lytic Viral Infections
2. Influenza
How do we catch it?
Contact with contaminated objects, droplet inhalation.
What are the symptoms?
Body Aches, Fever, Sore Throat, Nasal Congestion, Headache, Dry Cough, Fatigue.

18. Examples of Lytic Viral Infections
3. Ebola
How do we catch it?
exposure to blood or bodily secretions of an infected person, or through direct contact with the person.
What are the symptoms?
Sore Throat, Fever, Dry hacking cough, Weakness, Severe Headache, Joint and muscle aches, Diarrhea, Dehydration, Stomach pain, vomiting, Internal and external bleeding.

19. Examples of Lysogenic Viral Infections
1. Herpes Viruses
Once a person is infected with a herpes virus they are infected for life.
Examples:
Chicken Pox can reappear later in life as Shingles
HSV-1 (oral herpes) and HSV-2 ( genital herpes)

20. Example of a Retrovirus
2. HIV
How do we catch it?
Contact with contaminated blood or bodily fluids
What are the symptoms?
T cells (needed for normal immune function) are destroyed

21. Retroviruses
Retroviruses are viruses that contain RNA as their genetic information
Retroviruses get their name from the fact that their genetic information is copied backward, from RNA to DNA.
HIV is the most infamous retrovirus

22. How Do Our Bodies Fight Viral Infections?
Antibiotics do nothing for viral infections!!!
After enough cell debris (from blown up cells) is detected your Immune system gets involved
Macrophages are large white blood cells that get rid of debris by eating it.
When they eat too much, they die. These dead cells and the cell debris are “puss”

23. How Do Our Bodies Fight Viral Infections?
T- cells (thyroid cells) are called upon and go to the site of the infection to kill specific infected cells
B-cells (bursal cells) make antibodies that go to the site and kill free viruses
Other white blood cells pick up viral particles from the battle and carry it to Lymph nodes.
In the lymph nodes, they look for cells to fight this type of virus.

24. How Do Our Bodies Fight Viral Infections?
The best way to protect against most viral diseases lies in prevention, often by the use of vaccines.
Most vaccines provide protection only if they are used before an infection begins.