VIRUSES https://www.youtube.com/watch?v=UEKS4w9bfJg

Viruses Viruses are infectious agents with both living and nonliving characteristics

Viruses 1. Living characteristics of viruses a. They reproduce but only in living host cells b. They can mutate 2. Nonliving characteristics of viruses a. They contain no cytoplasm or cellular organelles b. They must replicate using the host cell's energy and materials (Viruses don't grow and divide on their own) c. The vast majority of viruses possess either DNA or RNA but not both.

Why are viruses not considered living? Viruses must invade healthy cells in order to reproduce. They are known as parasites.(They need a host cell function) Viruses that infect bacteria are known as bacteriophages 

The Structure Of a Virus Viruses are composed of two parts: A Protein Coat Inner core of genetic material The Inner Core of nucleic acid is surrounded by a protein coat called a capsid The Nucleic core is either made up of DNA or RNA but never both

How Viruses Multiply VIRUSES CAN EXHIBIT TWO TYPES OF LIFE CYCLES. 1. Active Viruses (Lytic Cycle) 2. Hidden Viruses (Lysogenic Cycle) SOME VIRUSES ARE ACTIVE ALL THE TIME. SOME VIRUSES CAN BE HIDDEN AND BECOME ACTIVE LATER. (See pages 212 and 213)

Active vs. Hidden Viruses 3 Prophage in chromosome Attachment 1 Lambda phage 2 Entry Active Cycle Hidden Virus Cycle 6 Synthesis 8 Release 4 Replication of chromosome (and progeny) cell division 7 Assembly Further cell division replications 5 Induction

Cool Video Clips http://www.youtube.com/watch?v=Rpj0emEGShQ& feature=related

Viral Replication The Lytic (Active) and Lysogenic (Hidden) Cycles: How HIV (a retro-virus) replicates and causes AIDS http://glencoe.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::550::400::/sites/dl/free/0078802849/383942/Retrovirus_Replication.swf::Retrovirus%20Replication http://glencoe.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::550::400::/sites/dl/free/0078802849/592996/hiv.swf::HIV http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter17/animation_quiz_2.html

How small are viruses???? Viruses are so small that most can only be seen by the electron microscope ( 1935-tobacco mosaic virus) 17-300 nanometers long (one millionth of an inch) and about one thousand times smaller than bacteria can only grow in other cells (host cells)

Tobacco Mosaic Virus

Adenovirus

Smallpox

Ebola virus

Why do we get infected with some viruses but not others? Each virus is specific for the type of cell (respiratory, intestinal, bacterial) that they invade because the receptor sites on the virus must match up with the receptor site on the host cell (embedded in the plasma membrane) Example: Rhinovirus (cold virus) will only infect respiratory tissue

How did viruses evolve? Some people think that viruses were some of the first life forms Other people think that they are descendents of complex living organisms but they dropped or lost their cell structure Others think they arose from DNA that escaped from cellular organisms Some even think they came from aliens (Mr. Kay)

What works against viruses? Vaccines or immunizations By pre-infecting the body with small amounts of a particular virus, our body can build up antibodies that will fight it for our lifetime * Antibiotics DO NOT work against viruses because they attack cell walls (which viruses do not have)

Vaccine Antigens (Dead/Weakened Viruses) are deliberately introduced into the immune system to produce immunity Because the virus has been killed or weakened, minimal symptoms occur Have eradicated or severely limited several diseases from the face of the Earth, such as polio and smallpox

Cell before infection… Viruses Viruses enter body cells, hijack their organelles, and turn the cell into a virus making-factory. The cell will eventually burst, releasing thousands of viruses to infect new cells. …and after. Cell before infection…

The Second Line of Defense ~Interferon~ Virus-infected body cells release interferon when an invasion occurs Interferon – chemical that interferes with the ability to viruses to attack other body cells What happens to already infected cells?

White Blood Cells ~T-Cells~ T-Cells, often called “natural killer” cells, recognize infected human cells and cancer cells T-cells will attack these infected cells, quickly kill them, and then continue to search for more cells to kill

The Third Line of Defense ~Antibodies~ Most infections never make it past the first and second levels of defense Those that do trigger the production and release of antibodies Proteins that latch onto, damage, clump, and slow foreign particles Each antibody binds only to one specific binding site, known as an antigen

Vaccine Antigens (Dead/Weakened Viruses) are deliberately introduced into the immune system to produce immunity Because the virus has been killed or weakened, minimal symptoms occur Have eradicated or severely limited several diseases from the face of the Earth, such as polio and smallpox

Vaccines Viruses grown on chicken embryos are attenuated vaccines Another type of vaccine is made by heat killing the virus