Viruses and Bacteria

1. Viruses and Bacteria Antibiotics work on Bacteria, NOT Viruses!

2. Viruses • Protein coat • Requires a host cell to replicate • Smaller than a prokaryote (10-400nm) • (ex. HIV, influenza/flu)

4. Viruses binds to receptors on a cell’s plasma membrane • Viruses are organism specific because of these receptors! • Viruses have attachment proteins on their surface. • Examples – a plant virus cannot infect an animal cell, a T4 Bacteriophage cannot infect a skin cell

5. Viruses are NOT alive! use the cellular machinery of another organism’s living cells to multiply themselves Tail of the virus attaches to host injects its DNA or RNA into the host. Host cell cannot tell the difference between its own DNA and that of the virus Cell replicates the viral DNA as if it were its own. Thousands of copies of the viral DNA and protein coat are made. Eventually the cell becomes too full and lyses (bursts) releasing hundreds of virus particles that can now infect other cells. Viral InfectionLytic Cycle of a Virus

7. The virus reproduces itself, but does NOT lyse the cell. Viral DNA is injected and becomes incorporated into the cell’s DNA unknowingly. The inserted viral DNA is called a Provirus. The virus can remain inactive like this for long periods of time When the cell replicates, so does the virus! Sudden changes (temperature or availability of food) may cause the DNA of the prophage to become active. Now new viral DNA could be synthesized like in the Lytic cycle Lysogenic Cycle of Viruses

11. Retroviruses (backwards) • Instead of DNA, Retroviruses infect cells with RNA. • RNA is then copied into DNA by an enzyme called Reverse Transcriptase and inserted as a prophage like the lysogenic cycle. • HIV is a retrovirus • Retroviruses mutate very easily, making them resistant to treatment - the problem with HIV

12. Viruses are not always bad!! • Viruses are commonly used in genetic research. • The viral genetic info can be removed and replaced with new genetic information • These modified viruses - called vectors - can then be inserted into other organisms, allowing the virus to inject its new (good) genetic info into the target cell.

13. Bacterial Structure (prokaryote) • Lacks membrane bound organelles • Except they do have small ribosomes! DNA is typically circular, not in chromosome form

14. Identifying Bacteria • Gram Staining - Stain affects bacteria differently based on their cell wall structure • Gram positive = Purple • Gram negative = Pink • Shape - 3 Shapes are most common • Cocci - round • Bacilli - rod-shaped • Spirilla - Spiral streptococcus Bacillus Spirulina