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Biology Microbes / Classification 2012 – 2013 #1 I. Discovery of viruses A. Tobacco Mosaic Virus 1. pathogen (any disease causing agent) must be very small -‐ smaller than any known bacteria II. Structure of viruses A. Envelope = glycoprotein covering that has specific receptor sites B. capsid = protective protein covering 1. head = hollow sphere that holds the genetic material -‐ DNA or RNA (never both) inside 2. tail fibers = allow the virus to “land” on the host III. Action of viruses A. viruses attach to a cell (specific) B. viral DNA (or RNA) is injected into the host cell C. viral DNA takes over and causes the cell to make viral parts (lytic cycle) or it can remain dormant (lysogenic cycle) D. viral parts are put together inside the host cell E. cell bursts open releasing hundreds of new viruses
