To Figure Out What You Need on the Final… Score needed= (Goal - 0.8*Current Grade)/0.2 E.g. you have a 58. To pass the class Score needed = (59.5-0.8*58)/0.2 = 65.5

Runaway Genetic Material Viruses Runaway Genetic Material

What is a virus? Genetic material (DNA or RNA, single or double stranded) A protein coat Sometimes a few more proteins Sometimes a membrane

Notice viruses have… No organelles of any kind No ribosomes Can’t really make or do anything on their own

Why aren’t viruses considered living? No homeostasis No growth No real metabolism No real response to environment Not organized into cells Reproduction is dependent on host They do adapt/evolve

What do Viruses Do? Insert genome into a host Replicate using host machinery (DNA polymerase, RNA polymerase, ribosomes) Reassemble and infect new hosts

Types of Viruses DNA Viruses RNA viruses Retro viruses Makes copies and leaves cell E.g. cold, flu, rabies, ebola Use reverse transcriptase to make DNA from RNA Insert themselves into the genome E.g. HIV May insert into host or just copy and leave E.g. chickenpox, smallpox, herpes, hepatitis B

Retroviruses Retroviruses like HIV insert DNA into our genome Once there it’s near impossible to remove Can transcribe to make new viruses and proteins that are necessary to assemble new viruses

Where Did Viruses Come From? Viruses are extremely diverse, so it seems unlikely that all viruses are related 3 main hypotheses, all of which could be correct

1. Viruses “escaped” from host Viruses tend to be genetically similar to hosts Genes move and copy themselves in similar ways to many viruses

2. Viruses were living things that lost most of their machinery Many parasitic bacteria like Chlamydia are thought to have evolved from free-living ancestors Over time parasites lose genes and become much smaller and simpler

3. Viruses were here first Viruses are the most primitive organisms and have co-evolved with new forms of life

Why is it Hard to Treat Viruses? There’s nothing to attack! Antibiotics attack the cell wall of bacteria or their ribosomes. Viruses have neither They mutate often due to lack of proofreading (especially retroviruses) Once they are part of the genome there’s no real way to attack them

Vaccines Piece of a virus (e.g. one protein) or inactivated virus Stimulates immune system to create antibodies ahead of time Prevents virus from invading cells in the first place

Self-Destruction Your immune system recognizes infected cells and destroys them

Viruses are Necessary Keep bacteria in check Estimated to kill 20% of the biomass of the ocean each day Recycles nutrients and provides new opportunities for other organisms

Review For the test you should know: the basic structure of a virus why viruses are not considered living how a retrovirus operates the 3 potential origins for viruses how our body deals with viruses You DO NOT need to know Specific viruses other than HIV The specifics of how T cells operate Specifics on how DNA or RNA viruses operate (just know they copy themselves, make proteins and reassemble The fun facts

Fun Facts About Viruses About 8%-50% of the human genome is thought to have originated from infectious viruses About 1030 viruses on Earth. Lined up end to end they would stretch 200 million light years out! (longer than the entire length of our galaxy) 1016 copies of HIV are generated each day A liter of seawater contains 100 billion viruses HIV has only about 10 genes. The smallest virus ever discovered has only 2 genes http://www.virology.ws/2009/10/19/ten-cool-facts-about-viruses/ http://discovermagazine.com/2010/apr/20-things-you-didnt-know-about-viruses