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Animal Viruses • Because viruses are lifeless partials, their spread depends on other agents. • A( ) is an intermediate host that transfers a pathogen or parasite to another organism • Classified as ( ) or ( ) viruses, ( ) or ( )stranded • Many have envelopes with glycoproteins that are specific for receptors. • The glycoproteins are made by the ER and added to the host cell’s membrane which envelopes the emerging viruses. Fig. 19-7 Capsid and viral genome enter the cell Capsid RNA HOST CELL Envelope (with glycoproteins) Viral genome (RNA) Template mRNA Capsid proteins ER Glycoproteins Copy of genome (RNA) New virus Table 19-1a Table 19-1b RNA Viruses • The broadest variety of RNA genomes is found in viruses that infect animals • ( ) use ( ) to copy their RNA genome into DNA (HIV is ex.) • The viral DNA that is integrated into the host genome is called a ( ) • Unlike a prophage, a provirus remains a permanent resident of the host cell Fig. 19-8a Glycoprotein Viral envelope Capsid Reverse transcriptase RNA (two identical strands) HOST CELL HIV Reverse transcriptase Viral RNA RNA-DNA hybrid DNA NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation New virus mRNA Fig. 19-8b HIV Membrane of white blood cell 0.25 µm HIV entering a cell New HIV leaving a cell Viral diseases in animals • Symptoms caused by - toxins - body’s defense mechanisms • ( ) – weakened or derivatives of viral particles capable of causing an immune response • ( ) not effective • Some antiviral medications interfere with viral ( ) synthesis Where do new viruses come from? •( ) of existing viruses • The dissemination of an existing virus to a more widespread population • Or spread between species •( ) – general outbreak of a disease •( ) – global epidemic Fig. 19-9 (a) The 1918 flu pandemic 0.5 µm (b) Influenza A H5N1 virus (c) Vaccinating ducks Plant viruses • More than 2,000 types of viral diseases of plants are known and cause spots on leaves and fruits, stunted growth, and damaged flowers or roots • Most plant viruses have an RNA genome • Plant viral disease can spread by vertical transmission from parent plant or by horizontal transmission from an external source. Fig. 19-10 Viroids and Prions: The Simplest Infectious Agents • ( ) are circular RNA molecules that infect plants and disrupt their growth • ( ) are slow-acting, virtually indestructible infectious misfolded proteins that cause brain diseases in mammals • Prions propagate by converting normal proteins into the prion version • Scrapie in sheep, mad cow disease, and Creutzfeldt-Jakob disease in humans are all caused by prions Viroids in Plants Fig. 19-11 Misfolding of proteins to form prions Prion Normal protein Original prion New prion Aggregates of prions Scrapie in sheep