+ Viruses and Prions

+ What is a virus? DNA enclosed in a protein shell They are not alive Need cells to survive

How do they work? Insert their DNA or RNA into a host cell. Uses the host environment to replicate DNA or RNA using enzymes. Assembles proteins and enzymes in the host cell. Assembles new viruses. Exits the cell taking the cell membrane with it

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Why are they so dangerous? Viruses kill the cells they use for replication. They can replicate quickly. They are not alive so it’s hard to kill them. Affect every cell differently

Ex #1- Herpes Virus Herpes Viruses reproduce in the host cell’s nucleus. Can live dormant in host cells. When under stress (cold, sunburn) the DNA will replicate and produce the symptom. (A cold sore)

Ex #2: Polio Virus Infects nerve cells. Nerve cells do not replicate(meaning once they are gone they are gone forever.) Polio causes permanent damage. It’s hard to find cures for such viral diseases that do not harm the host cell. Poliovirus FDR

+ Ex #3: HIV/AIDS HIV is a virus that contains RNA as well as other special enzymes.(reverse transcriptase) Able to use RNA to make DNA. Inserts DNA into host DNA Host cell produces viral RNA and proteins

HIV continued… Most viruses only use their RNA or DNA to produce more viruses. HIV is able to become part of the host cell making it a provirus. Infects and kills white blood cells

Prions A misfolded protein that interrupts normal cell function. Affects brain and nervous tissue Do not contain DNA or RNA Responsible for diseases such as mad cow disease and Creutzfeldt-Jakob disease