Kingdom: Viruses Biology 11 G. Burgess 2009 What’s a virus Complex molecules made of a protective protein coat that either covers a RNA or DNA segment. They are not ‘living’ yet are able to reproduce They must interact with a living cell in order to generate new viral complexes Structure of a virus Protein Coat Protein attachment sites RNA segments •Every fall/winter we are infected with the flu virus. •As the virus is transferred from one host to another, the RNA is changed by our own cells. •The proteins on the outside of the virus allow it to attach to proteins on our cell membranes. Once attached, the virus is able to release its RNA into our cells to take control of ribosomes and make copies of itself. Classification of Viruses Viruses are first classified by their host Viruses infect all living organisms from monera to fungi to animalia. MORPHOLOGICAL CLASSIFICATION They are also classified by their biochemical make up and structure GENOMIC CLASSIFICATION The Baltimore Classification System Classifies viruses into seven groups by comparing their nucleic acid (DNA or RNA), strandedness (single-stranded or double-stranded), and method of replication. Group I: double-stranded DNA viruses Group II: single-stranded DNA viruses Group III: double-stranded RNA viruses Group IV: positive-sense single-stranded RNA viruses Group V: negative-sense single-stranded RNA viruses Group VI: reverse transcribing Diploid singlestranded RNA viruses Group VII: reverse transcribing Circular doublestranded DNA viruses DNA viruses Group 1 Double stranded DNA ie. Herpesviridae (herpes) Poxviridae (small pox) Group 2 Single strand DNA ie. Parvovirus Human Papilloma virus Gynecological tests check for signs of this cervical cancer causing virus. RNA viruses Group 3 Double strand RNA Ie. Rotaviruses Group 4 Positive-sense single RNA strand ie. SARS virus, rubella virus, polio, HIV Group 5 Negativesense single RNA strand ie. Measles, mumps, rabis RNA Small pox, Variola virus Life Cycle of a virus 2 parts; lytic and lysogenic cycle Lytic cycle: Virus identifies and infects a host cell Virus takes control of cell’s organelles (namely the ribosomes) and self replicates using the materials within the cell. Once new viruses are generated, the virus causes the host cell to lysis(break open) and release the newly created viruses. Functioning Cycle of a virus Lysogenic Cycle: Viral DNA may infect the host cell’s DNA. This is called a provirus. Proviruses do not allow other viruses to infect the cell They may carry on normal everyday activities of the cell or cause changes in the cell or organism over time. These viruses are stimulated by environmental factors causing the production of new viruses and the lysis of the host cell. Questions Pp. 338 #1-8 Text: Biology 11, Nelson, 2002. Bibliography Biology Living Systems, Glencoe, 1994. Virus Types, http://www.mansfield.ohiostate.edu/~sabedon/biol3025.htm, S.Abedon, accessed Nov.8, 2006 ManBir Online, http://manbir-online.com/index.htm, accessed Nov.8,2006. ICTVdB, http://phene.cpmc.columbia.edu/, Dr.C.Büchen-Osmond, accessed Nov.8, 2006.