1. Structure, Reproduction & Disease
The Virus
Structure, Reproduction & Disease

2. Virus Structure Viruses differ in shape and structure.
All viruses have either DNA or RNA inside. The DNA/RNA is a set of instructions for the production of new viruses.
This genetic material is enclosed in a “protein coat” called a capsid.

3. Virus Structure There may also be a fatty acid layer.

4. Virus Shapes You don’t have to know all the details shown here, just that there are a variety of shapes and sizes.
Plant Virus Animal Viruses Bacteria Virus

5. Virus Reproduction Viruses do NOT and CANNOT reproduce on their own.
They MUST get their DNA instructions into a host cell.
The host cell will read those instructions which say “Make
more viruses.”
The host cell will then follow the instructions and make
more viruses.
The viral DNA may also direct the host to finally produce
digestive enzymes to break down the cell wall, releasing
the new viruses.

6. Bacteriophage Often called simply “phages
Bacteriophage Often called simply “phages.” Virus that invades bacteria.

7. Bacteriophage Often called simply “phages
Bacteriophage Often called simply “phages.” Virus that invades bacteria.
T.E.M. Images
T.E.M. stands for Transmission Electron Microscope

8. Bacteriophage Often called simply “phages
Bacteriophage Often called simply “phages.” Virus that invades bacteria.
This is a colorized T.E.M.
What does T.E.M. stand for?
Bacteriophage or “phage”
Bacterial Wall
Bacteria’s cytoplasm

9. Bacteriophage Virus that invades bacteria.
Capsid - “Protein Coat” – contains DNA.
The spikes that look like legs are proteins that help attach to proteins on the bacterial cell wall.
The tail sheath releases a digestive enzyme (a protein) that begins to digest or break down the bacterial wall.
The sheath then contracts,
punching a hole in the bacterial
wall and injects the DNA into the
bacteria.

10. Viruses That Infect Eukaryotes
Review: A “Eukaryote” is any organism other than a bacteria. Eukaryotes have a nucleus.
May enter the cell by a process called endocytosis.
Endo: “Entering” or bringing into the cell.
Cytosis: Think cytoplasm (contents of the cell)

11. Viruses Infecting Animal Cells T.E.M. Images

12. Viruses Can Cause 2 Types of Infections
Although it varies how the viral DNA get’s into the cell, all viral infections follow one of two basic pathways.
Lytic Infection: The host cell dissolves (lyses) releasing new viruses which then infect surrounding cells.
Lysogenic Infection: The viral DNA is joined with the host cell’s DNA. When the cell divides into 2, it copies it’s DNA and therefore copies the viral DNA. Both offspring cells carry the viral DNA.

13. Bacteriophage Lytic Cycle Lyse: “To cause the disintregration of a substance.” To make it “dissolve”.
After new viruses are produced, the viral DNA directs the cell to produce enzymes to lyse the cell wall, releasing the viruses.

14. Bacteriophage Lysogenic Cycle Genesis: Creation or the beginning
Bacteriophage Lysogenic Cycle Genesis: Creation or the beginning. Think NEW bacterial cells are produced that carry the virus.
The viral DNA is incorporated into the bacterial DNA. The cell reproduces and each new bacteria carries the virus.

15. Lytic vs. Lysogenic Cycles
The viral DNA is incorporated into the bacterial DNA. The cell reproduces and each new bacteria carries the virus.

16. How Immunizations Work
NOT a cure.
Prepares the body for a future attack.
Immunization cannot be after you get infected.

17. Antiviral Medications
Drugs given AFTER infection.
Do NOT “kill” the virus. How can you kill that which is not alive?
Do NOT cure the disease.
Some slow viral reproduction… slows the infection. This allows your immune system a chance to get ahead.
Less severe infection.
Faster recovery.
Some alleviate symptoms. Make you feel better.

18. Example Antiviral “Tamiflu”
One of the proteins on the Influenza virus, “Neuraminidase”, helps the viruse break through the cell membrane to infect the cell.
Tamiflu has chemicals that bind to (stick to) the Neuraminidase molecule.
This stops the virus from infecting the cell.
If taken within 48 hours of contracting the flu, Tamiflu can decrease the length and severity of the infection.

19. Some Common Viral Diseases NOT ON TEST.. JUST FOR “FUN”
Herpes
8 types in humans
Breaks out when the person’s immune system is under stress
Never fatal
No vaccine
No cure
Some antivirals make duration of outbreak shorter

20. Some Common Viral Diseases
Influenza
Common name the Flu
Thousands of variations and can reinfect people each time
Runny nose, coughing, sneezing, fever, tired, sore joints
Can get the flu shot for the current years strains (vaccine)
Can be fatal

21. Some Common Viral Diseases
Chicken Pox
Causes a blister-like rash on the surface of the skin and mucous membranes
Some have a fever, abdominal pain or a vague sick feeling
Can be fatal
There is now a 2 part immunization

22. Some Common Viral Diseases
Small Pox
Highly contagious sometimes fatal
No treatment
Prevention in the form of a vaccine
Eradicated from the planet, but now there is a fear of its use as a bioterrorism weapon