1. The Genetics of Viruses and Bacteria Chapter 18

2. Viruses A virus is a small infectious agent that can only reproduce inside the living cells of organisms. Technically, viruses are NOT considered to be alive. They are too small to be seen with light microscopes, they are smaller than ribosomes. Millions of viruses can fit on the head of a pin. Viruses can cause: flu, HIV, Herpes, the common cold, EBOLA

3. Viruses Viruses are made of nucleic acid (either DNA or RNA) enclosed in a protein coat. Viruses that infect bacteria are called bacteriophages or simply phages.

4. Viral Structure Tobacco mosaic virus has a helical capsid with the overall shape of a rigid rod. This was the first virus discovered, and it affects the tobacco plant.

5. Viral Structure Bacteriophages have a complex capsid consisting of a polyhedral head and a a tail apparatus. These viruses infect bacteria.

6. Viral Reproduction Viruses can reproduce two ways, through the lytic cycle and the lysogenic cycle. The lytic cycle causes death to the host organism. The lysogenic cycle replicates the nucleic acid of the virus without killing the host.

7. HIV HIV stands for human immunodeficiency virus. It is a retrovirus that causes AIDS (acquired immunodeficiency virus). HIV has single stranded RNA enclosed in an envelope. Once the RNA is released, HIV can replicate its own RNA and even make its own proteins. At this time, an HIV infection cannot be stopped or removed from the host.

8. Vaccines Vaccines are harmless variants or derivatives of pathogenic microbes that stimulate the immune system to mount defenses against the actual pathogen.

9. Bacteria Bacteria can reproduce rapidly, and often mutate. The genetic material of bacteria is called the nucleoid, which is a tightly coiled, very long strand of DNA.

10. Mutation By using antibacterial soap (and antibiotics) all we are doing is ensuring that the strongest bacteria survive and reproduce. This accelerates bacterial evolution and creates super bugs, such as MERSA. This is how people develop antibiotic resistance, their bacteria is too strong to be destroyed by regular antibiotics.

11. Operons Genes that can be turned on or off as needed. The switch that does this is a segment of DNA called an operator. Along with an operator, there is a promoter and some enzymes that make up the operon. Repressors turn off an operon Inducers turn on an operon

12. Trp operon Tryptophan is an amino acid that is usually produced by the body but can be turned off. This is a “repressible operon”

13. Trp operon http://www.dnatube.com/video/324/The-Tryptophan- Operon

14. Lac operon The lac operon is usually off but can be stimulated (induced) and is therefore called an “inducible operon.” The lac operon functions in the digestion of lactose, milk sugar.

15. Lac operon http://vcell.ndsu.edu/animations/lacOperon/movie.h tm