Question of the day Q: What relationship do some bacteria have with their host organisms? A: Q: Name a situation where bacteria is “helpful”.

Question of the day: 1/27/10 Q: A cube has a length, width and height of 1cm. What is the volume of this cube? A: Q: What is the definition of volume?

Chapter Seven: The Microscopic World 7.1 Protozoans 7.2 Bacteria 7.3 Viruses

7.3 Viruses Viruses are not made of cells. A virus is a tiny, nonliving particle made up of genetic material and protein. A virus’ only job is to find a “host cell” and infect it. A host cell is the cell that is infected by the virus Reproducing viruses caused this cell to burst.

7.3 How viruses infect cells 2 ways viruses come into contact with the host cell: 1. trigger the host cell to engulf the virus 2. Fuse into the cell membrane A cell membrane controls what enters a cell. The virus “tricks” the cell through a “lock and key” mechanism. If the virus has a protein that fits a receptor on the cell membrane, the cell will allow the virus to enter.

7.3 How viruses infect cells Once in contact, the virus inserts its DNA into the host cell. Host cell produces new viruses Infected cells burst and die, freeing new viruses, so the cycle can start again.

7.3 The spread of virus and immunity Normally your immune system protects your cells from viruses and bacteria. Antibodies prevent viruses from entering cells.

7.3 Vaccines A vaccine is a preparation made from weakened virus particles or their empty protein coats. A vaccine causes your immune system to produce antibodies to a particular virus. When you come in contact with the real virus, your immune system can respond more quickly to produce antibodies and prevent illness.

7.3 Vaccination

The Good, The Bad, The Microbe Ecology Connection The Good, The Bad, The Microbe Microbes are organisms too small to see with the human eye.