CH.11 Sections 1

Viruses

Viruses

 A virus is a tiny

non-living

particle that enters and reproduces inside a host cell.

 A virus is like a parasite – in that it needs a host in order to live.

Virus Shapes

 Viruses vary in shape  Round  Rod-shaped  Shaped like bricks  Shaped like threads  Shaped like bullets  Robot-like shape  Bacteriophage – robot shaped- a virus that infects bacteria.

Virus Size

 Viruses are very tiny. They cannot be seen with a compound microscope  They are smaller than cells  Measured using nanometers.

 1 nanometer is 1 billionth of a meter.

Structure of Viruses

  All viruses have a similar structure Viruses have two basic parts: 1. Protein Coat – protects the virus - contains surface proteins that allow the virus to attach to certain cells - Lock and key – viruses can only attach to a few certain cells 2. Inner Core made of genetic material - contains instructions for making new viruses



Active

viruses enter cells and immediately begin to multiply, leading to the quick death of the invaded cells.

- Viruses

Hidden

viruses “hide” for a while inside host cells before becoming active.

Viruses – Good or Bad?

 Some viruses cause disease while others are very useful – useful in gene therapy   Some viruses like a cold or flu are often short lived.

HIV – is a deadly virus for which there is no cure – eventually becomes AIDS.

 Viruses can affect other organisms other than humans. Plants, dogs and cats can all have viruses.

Some Common Infectious Viruses

 Influenza – Flu  Hepatitis  AIDS  Malaria  Pneumonia  Polio  Strep

Vaccines

 A vaccine is a substance introduced into the body to stimulate the production of chemicals that destroy specific viruses or bacteria.

 Vaccines are either dead or altered viruses.