1. Viruses

2. What to Know: Learning Objectives
Overview:
What are some basic facts about viruses?
Structure:
What are the shapes?
Reproduction:
What is the lytic & lysogenic pathways?
Infection:
How do they get into cells and then get reproduced?
How do they get treated?
Describe a few common or well-known virus.
AIDS, the common cold, hepatitis, influenza
What are viroids & prions?

3. Viruses Infectious particles (not living cells).
Very small in the biological world (hundreds times smaller than the cells they infect).
Science is still not sure how or why viruses came about, but they are integral in all species (no real benefit to living species).
Major source of disease and genetic diversity in the living world (diversity comes from the mutations virus cause).
Typically named after the disease they cause or the tissues they infect.

4. Virus Classification Classification not typical:
Defies biological classification.
Classified or grouped various ways
Morphology: Shape & structures
What is infected: Plants, animals, bacteria
Genetic composition: DNA, RNA, single or double-stranded
Pathology: nature of the disease

5. Virus Structure Simple virus structure
*Genetics… this is the direction to make more virus
*Body… Surrounded by proteins (capsid)
May or may not have an additional covering (envelope)
Many have protein capsid with surface markers (like keys) that are designed to fit locks in the cells of species they have evolved to infect.
Virus Structure
* All virus have these two features

6. Each have their own form but can be categorized:
Viral Shapes
Each have their own form but can be categorized:
Helical
Polyhedral
Enveloped/Spherical
Other.

7. Helical
Polyhedral
Enveloped
Others

8. Viruses: Living or Not? Considered to be non-living (debated) Living
Does not meet all of the characteristics of life
Living
Non-Living
-Contains genetic material (RNA/DNA)
-Reproduce (in host)
-Has organization
-Do not have cells
-Do not respond to stimuli
-Do not use energy
-Do not grow & develop
-Cannot reproduce on their own

9. Virus v. Bacteria

10. Virus & Disease
By virtue of their very existence, virus are infectious particles.
They MUST infect a living host to reproduce.
In the process, they interrupt host life functions in a variety of ways.
This interruption causes the disease.
Their pathology (characteristics of their disease process)

11. Transmission of Viral Disease
Virus are pathogenic…
They cannot reproduce unless they attack another cell.
…and carcinogenic.
Once in the cell the have a tendency to cause irreparable genetic damage that can lead to cancer.
HPV & Cervical cancer
Hepatitis B & C & Liver cancer
T Lymphotropic & Leukemia
Possible ways to become infected are
Bites
Physical contact
Body fluid
Mother to child
Contact in the air
Sexual contact
Environmental exposure

12. Viral Reproduction Viruses must have a living host cell to reproduce
Example: Bacteriophages infect bacteria
Example: Herpes Simplex 1 infects lip cells
Virus insert their genetic information inside the host cell and use the host cell to make more virus particles

13. Viral Replication Lytic cycle Viral DNA is injected into host cell
Contains instructions needed to make more viruses
Host cell replicates viral DNA and makes the viral capsids (protein coats)
New viruses are assembled inside host cell
Cell bursts open releasing new viruses

14. Lytic Cycle D. Cell bursts open releasing new viruses
A. Viral DNA is injected into host cell
C. New viruses are assembled inside host cell
B. Host cell replicates viral DNA and makes the viral capsids (protein coats)
Lytic Cycle

15. Viral Replication Lysogenic cycle
Viral DNA is injected into the host cell
Viral DNA inserts itself into the host’s DNA
Remains inactive for days, months, or years
As the cell reproduces, more cells are produced that have the viral DNA in them
Eventually, when the conditions are favorable (like when your immune system is weakened) the virus will enter the lytic cycle

16. Lysogenic Cycle

17. Lysogenic & Lytic Cycles: These integrate for dormant-type virus
A Virus particle binds, injects genetic material.
Lytic Pathway
A1 Viral DNA is inserted into host chromosome by
viral enzyme action.
Lysogenic Pathway
E Lysis of host cell
lets new virus particles escape.
A2 Chromosome and integrated viral DNA are replicated.
B Host replicates viral genetic material, builds viral proteins.
A3 Cell
divides; recombinant DNA in each daughter cell.
D Accessory parts are attached to viral coat.
C Viral proteins self-assemble into a coat around viral DNA.
A4 Viral enzyme excises viral DNA from chromosome.
Figure 21.4
Pathways in the multiplication cycle of a bacteriophage.

18. Pertussis (whooping cough)
Treatment of Virus
Antibiotics: Do not work on viruses…
they are not living
Virus treatment options:
Antivirals: specific for infection
Tamiflu®, Relenza®, etc.
Body’s natural defenses: Immune system
Rest
Antioxidants
“Feed a cold, starve a fever”?
Vaccines are taken beforehand to prevent infections by introducing the immune system to viral recognition signals.
Subject to controversy…
Common Virus Vaccines
Hepatitis A
Hepatitis B
Influenza (the “Flu”)
Measles, Mumps, Rubella
Pertussis (whooping cough)
Rabies
Polio
Tetanus
Meningitis

19. Video clip Write 5 facts from the video
/flu-attack-how-a-virus-invades-your-body
Get into groups, divide the chapter up into sections, read through and gather information, answer the questions.

20. Here's a better, longer answer than the one in the video
Here's a better, longer answer than the one in the video. First, some new viruses get caught in mucus and other fluids inside your body and are destroyed. Other viruses get expelled in coughs and sneezes. Second, lots of those new viruses are lemons. They don't work that well. Some don't have the right "keys" to invade healthy cells so they can't spread the infection. And third, as the animation shows, your immune system is busy attacking the viruses whenever and wherever possible.