Viruses
Viruses are microscopic (organisms?) which exhibit some characteristics of living things, but not all.
Viruses range in size from .01 micrometers to .5 micrometers
Viruses can’t reproduce on their own, but need a “host” cell.
Viral Structure
Typical viruses consist of two parts : a protein coat and a nucleic acid (DNA or RNA) core.
The DNA or RNA is the genetic “code” of the virus.
Viruses come in all different shapes and sizes, and have very different types of protein coats.
Viral Structure
Viruses have different types of protein coats, different shapes, and can have different genetic information (DNA,RNA)
Journal Activity #1
Use the website below to do the following activities: Describe the function of the capsid, envelope, and
nucleic acid of viruses.
Briefly describe how viruses are classified. What are the two basic shapes of viruses? What does a retrovirus do?
http://micro.magnet.fsu.edu/cells/virus.html
Reproductive Cycle of Viruses
Viruses can’t reproduce on their own, but need a “host”.
Viruses which infect, use the host cell to reproduce new viruses, and then kill the host cell are part of the process known as the Lytic Cycle.
Lytic Cycle
In the lytic cycle a virus will escape undetected into an organism, and attach itself to the cell wall or cell membrane or a “host” cell.
The virus will then release an enzyme to break down the cell membrane or cell wall, which will allow for the insertion of the viral DNA or RNA into the host cell.
The host cell will then manufacture viral parts, and the newly assembled viruses will explode and kill the host cell, and find other host cells to infect.
Lysogenic Cycle
Some viruses don’t kill their host cell (lytic), but enter the host and remain inactive for years.
Viruses which do this are in what’s known as the lysogenic cycle.
The lysogenic cycle includes attachment, replication, and “activation” at certain times. This activation phase usually results in the “lytic” cycle.
Journal Activity #2
Use the website below to answer the following questions? What does the word virus mean? Name two diseases caused by RNA viruses, and two diseases
caused by DNA viruses. Describe one theory of how viruses originated.
http://www.personal.psu.edu/faculty/w/x/wxm15/Online/Virology/virology_lec00.htm
Transduction
Viruses have the ability to transfer their genetic material into a host cell. This transferring of genetic material is known as transduction.
This transduction is now being used to insert “wanted” genetic information into certain human cells. (genetic engeneering)
Retroviruses
Retroviruses are viruses which contain RNA as their nucleic acid.
Retroviruses have a way to change their RNA into DNA and include this into the host cells DNA.
http://www.whfreeman.com/kuby/content/anm/kb03an01.htm
Viruses and Disease
Viruses cause disease in plants and animals by altering and destroying the hosts cells.
Disease causing viruses are termed pathogens.
Typical cold virus
History of Viruses
1892 : Russian biologist Dimitri Iwanowski found an “invisible” substance which caused disease in tobacco plants.
1898 : Dutch botanist Martinus Beijerinck repeated Iwanowski’s work and concluded the “invisible fluid” a virus (poison)
1935 : American Wendell Stanley isolated the tobacco mosaic virus.
Viral Infections
Viruses can cause minor infections, minor sickness, or serious, fatal diseases in their host.
Viruses tend to attack specialized cells of a host.
Cold : respiratory
Polio : nerve cells
Viral Infections
The ability of a virus to cause a disease is termed its “virulence”
Journal Activity #3
Use the internet and other resources to describe the following characteristics of each disease below.
a) Genetic material b) shape of virus
c) Target cells of host d) type of virus
e) Virulence e) lytic or lysosomic?
Diseases: cold, influenza, measles, smallpox, AIDS
Defense Against Viral Infections
Immunity : The natural defense against disease.
Immunity includes : Skin : viruses can’t penetrate. Mucous membranes: White blood cells : (phagocytes, T-cells,
etc, engulf and destroy viruses) Antibodies : produced in response to the
antigen(disease causing object)
Viral Protection
Immunity is categorized as active or passive.
Active : immunity resulting from the production of antibodies.
Passive: receiving antibodies produced in another person or animal. (unborn child)
Viral Protection
A body can produce a protein known as interferon, which interferes with viral replication.
Interferon protects against future replication for the attacking virus only.
Vaccine
A vaccine is a solution of weakened or killed pathogens (viruses).
The vaccine works to stimulate active immunity in a person by the introduction of the virus, and the production of antibodies for this antigen.
Flu-shot, polio, smallpox, chickenpox, hepatitis, etc.
Helpful Virus Websites
http://www.virology.net/Big_Virology/BVDiseaseList.html
*http://www.cdc.gov/ncidod/dvrd/disinfo/disease.htm
*http://www.mic.ki.se/Diseases/C02.html
