1. Viruses

2. What to Know: Learning Objectives
Overview:
What are some basic facts about viruses?
Structure:
What are the shapes?
Determine why virus are not alive.
Virus & Disease:
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
Reproduction:
What is the lytic & lysogenic pathways?
What are viroids & prions?

3. Viruses Viruses are: 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 known benefit to living species
Major sources of disease in the living world .
Major scientific debate over whether virus helped cause variation in species or not.
Typically named after the disease they cause or the tissues they infect.
Objectives
Overview:
What are some basic facts about viruses?
Structure:
What are the shapes?
Determine why virus are not alive.
Virus & Disease:
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
Reproduction:
What are the lytic & lysogenic pathways?
What are viroids & prions?

4. Virus Classification Classification is not typical:
Defies biological classification.
“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
Deadly, inconvenient, highly contagious or not, how it’s transmitted, etc.

5. Virus Structure Simple virus structure
*Genetics… this is the direction to make more virus
DNA, RNA, single or double-stranded.
*capsid… protein complex housing that forms its outer shell
+ 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.
* All virus have these two features

7. Each have their own form but can be categorized:
Viral Shapes
Each have their own form but can be categorized:
Groups:
Helical
Polyhedral
Enveloped/Spherical
Other.
See Your Handout!

8. Helical
Polyhedral
Enveloped
Others

9. Other Notable Virus Classification
Virus can be called “vectors”
Vectors: Transmitters of genetic information
For example: plasmids are vectors; genetic information is transferred from one bacteria to another.
Vectors transmit several ways:
5 Main categories; As DNA (3 types) or RNA (2 types)
Retrovirus: An RNA virus that infects host cells by reverse-transcribing DNA from RNA!
HIV (human immunodeficiency virus): this nasty retrovirus pathogen disguises itself by changing the surface markers when the immune system starts targeting it. This makes it difficult to eradicate without expensive antivirus treatment.
Viroids & Prions
Viroids: infectious RNA molecules that are transmitted like viruses
Prions: infectious protein particles

10. Viruses: Living or Not? Considered to be non-living (debated)
Does not meet all of the characteristics of life
In common with Living
Why they are 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

12. Human Disease
Virus
*Common cold
Rhinovirus
Chicken pox
Varicella-zoster virus
*Rabies
Rabies virus
Infectious Hepatitis
Hepatitis virus
*Measles
Measles virus
Polio
Polio virus
*Influenza
Influenza virus
*Ebola
Ebola virus
Mumps
Mumps virus
*AIDS
Human immunodeficiency virus
*Genital warts/Cancer
Human papillomavirus
Plant Disease
Tobacco mosaic
Tobacco mosaic virus
Potato leaf roll
Tomato leaf curl virus
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)
*These can be tested

13. Transmission of Viral Disease
Virus are pathogenic…
They cannot reproduce unless they attack another cell.
…and carcinogenic.
Once in the cell they can 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

14. Viral Reproduction Virus can be destroyed, but they can’t reproduce.
How do more virus get made?
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.
This process is broken down into 2 pathways.
The Lytic & Lysogenic Pathways of Viral Infections.

15. 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

16. 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

17. 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

18. Lysogenic Cycle

19. 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.
Figure 21.4
Pathways in the multiplication cycle of a bacteriophage.
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.

20. 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

21. 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.

22. 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.