Take 5 A cell that is virally infected appears to be bursting and dying under the microscope. Which infectious cycle is the virus undergoing? Sometimes viral DNA incorporates itself into the host's genetic material. What is the viral DAN called after this occurs? Viruses are ______________.

Viral Replication Lab Download the app “iMotion HD” Use this app to make an animation for the lysogenic cycle. You can do this with ONE partner or on your own. Must include: The whole cycle start to finish (each step) Captions or a voice over explaining each step of the lysogenic cycle You can use pictures, drawings, etc to make this project or edit it in iMovie (for the voice over) Submit it through ebackpack by the end of class

Viruses Ch 18.1

What is a virus? Example: flu (influenza) It kills 0.5 million people every year worldwide (30,000 in the US) A virus is 10X smaller than bacteria. A virus is composed of nucleic acids that are enclosed in a protein coat.

Are viruses living? NO! They do not grow, develop, nor carry out respiration Viruses can only replicate and they need a host cell to even do that.

How are viruses named? (part 1) After disease they caused rabies virus The organ/tissue they infect “adenovirus”  affects adenoid: tissue at back of throat/nasal cavity

How are viruses named? (part 2) Given a genus name ending in “virus” and a species name Virus that infects bacteria = “bacteriophage” or simply just “phage” Some have code names: Type 1 – Type 7, depending on what it infects

What is the structure of a virus?

An inner core of nucleic acid (DNA or RNA: which are the instructions for copying) Outer protein coat (aka “capsid”)

What is the structure of a virus? Some have an extra envelope on outside Many different shapes depending on what it infects

How do they attach to a host? By locking the proteins on the outside to a host or grabbing on with its tail fibers

How do they attach to a host? By locking the proteins on the outside to a host or grabbing on with its tail fibers

How do they attach to a host? The attachment is a specific process! Each virus can usually attach to only a few kinds of cells Example: polio virus can only infect intestinal and nerve cells

The viruses are species specific Ex: Smallpox virus infects only humans Ex: West nile virus infects birds, horses, and humans

Viral Replication Cycle Two cycles Lytic cycle Lysogenic cycle

Lytic Cycle http://www.youtube.com/watch?v=3DP-MAhr0YY

Lytic cycle Virus attaches to a host cell Injects DNA/RNA into the host cell Virus’ DNA is transcribed & translated Substances produced take over host cell’s genetic material Host cell provides enzymes and energy to make copies and assemble new viruses Viruses burst from cell (killing it)

Lysogenic cycle Doesn’t kill cell immediately like in lytic cycle Virus attaches and injects DNA/RNA Virus DNA/RNA is integrated into cell’s chromosome “Provirus”: viral DNA that is integrated into the host cell’s chromosome Cell carries out activities Every time cell replicates, provirus is replicated, too At any time, virus can be activated and enter lytic cycle (not sure what causes it. Ideas: stress, sunburn, anxiety) Ex: reoccurrence of cold sores

Lytic cycle vs. Lysogenic cycle

Disease symptoms of proviruses lysogenic cycles Disease symptoms of proviruses Cold sores: herpes simplex I virus Genital herpes: herpes simplex II virus Hepatitis B virus Chicken pox Shingles

Retroviruses Ex: HIV: human immunodeficiency virus causes AIDS Only has RNA Complex replication cycle Once inside host, a retrovirus makes DNA from its RNA using reverse transcriptase from inside its capsid Retroviruses It then integrates it into host cell’s chromosome (“provirus”)

HIV: An infection of white blood cells HIV attacks white blood cells Newly made viruses are released into blood stream to infect other white blood cells Infected cells function normally because provirus only makes a few new viruses at a time (person may not appear sick) You gradually lose white blood cells & can’t protect yourself against disease

Cancer and Viruses Some viruses linked to cancers Ex: hepatitis B may be causing liver cancer These viruses disrupt normal growth and cell division, causing abnormal growth (tumors)

Plant viruses Over 400 viruses that infect plants & 1000 diseases Viruses can stunt growth and cause yield crop loss They require wounds or insect bites to enter host Ex: Zucchini yellow mosaic virus

Plant viruses Viruses do not use surface recognition Do not undergo lytic or lysogenic phases Not all are fatal Ex: Tobacco mosaic virus

Hospitals “full up”: 1918 Influenza Pandemic Contagion Trailer: How a virus changes the world: http://www.youtube.com/user/takepart?v=qZTMT89EAHM Could “Contagion” Really Happen?