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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

Polio Facts

Roosevelt showed signs at age 39 – possible contracted it during summer camp as a child

The iron lung was used to help patients breathe

+Ex #3: HIV

• HIV is a virus that contains RNA as well as other special enzymes.(reverse transcriptase)

• It’s able to use RNA to make DNA.

• It inserts its DNA into host DNA

• The 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.

It infects and kills white blood cells

AIDS

Acquired Immune Deficiency Syndrome = AIDS

A person is diagnosed with AIDS when their immune system is too weak to fight off infections.

Prions

A misfolded protein that interrupts normal cell function.

Affects brain and nervous tissue

Does not contain DNA or RNA

Responsible for diseases such as mad cow disease and Creutzfeldt-Jakob disease