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Viruses & Prions What is a virus??? A virus is neither dead nor alive! What is to be alive? Characteristics for life... 1. Metabolism 2. Reproduction 3. DNA 4. Growth & Development 5. Response to environment 6. Maintain internal environment 7. Evolves Living organisms do not crystallize - viruses do. Viruses are made-up of either DNA (like smallpox) or RNA (flu, HIV) and protein. Some viruses also have lipids. A virus is basically a protein container (capsid) with nucleic acid inside. The only purpose of viruses is to reproduce. A virus is not considered alive since it must hijack the machinery of cells to copy itself. Viruses are generally specific as to what they infect. Plant viruses like the Tobacco Mosaic Virus, infect tobacco plants Animal viruses like influenza, infect certain animals (humans, pigs, ducks) Viruses that infect bacteria are called a bacteriophage. Influenza Virus Tobacco Mosaic Virus Potato Virus T4 Bacteriophage Viral infection When a virus has infected an organisms, there are two processes that can occur: Lytic infection or Lysogenic infection In lytic infection - as is the case with bacteriophage T4 a virus enters a cell, makes copies, and causes the cell to burst (Lyses). In lysogenic infection the virus integrates its genetic material into the DNA of its host. Then the host cell replicates its DNA along with the viral DNA - thus producing viruses indefinitely. Retrovirus These viruses contain RNA instead of DNA as their genetic material. A retrovirus gets its name "retro meaning backwards" because it copies RNA to DNA. Retroviruses can cause cancer in animals and some are well known such as HIV and Influenza. Reverse Transcriptase??? Viroids Single-stranded RNA particle without capsid ~ usually a plant affecting disease. Retrovirus Chicken Pox (Varicella) Measles (MMR) Smallpox (Variola) Eradicated, but what about terrorism? Smallpox PRIONS??? Mad Cow Disease or BSE (Bovine Spongiform Encephalopathy) and varient Creutzfeld-Jacob disease the human form - are thought to be caused by pathogenic proteins called prions. MAD COW DISEASE Mad cow disease is caused by something called a "PRION". A prion is a protein that is mutant (different than the normal kind) and causes normal proteins to change into mutant proteins when they come into contact with them. These pathogenic (disease causing) proteins can be obtained by eating tissue that contains it (like cow brains from an infected cow). It can also be passed down from mother to offspring animal ~ cow (inherited). This is possible because proteins are built from the instructions found in the organism's genes (DNA). If the organism has a bad gene for this disease, it will be passed to the offspring. The End