Kari Sanders 1 BSC 1005 Viruses Human Disease Study Guide Chapter One Overview Terms RNA or DNA enclosed by a protein coat Virus An obligatory intracellular parasite that carries a nucleic acid genome o A virus is NOT a cell A viral genome carries limited information A virus lacks the ability for metabolism it replicates inside a cell and cannot survive long outside the host cell But a virus lives a cushy life without doing much itself Viruses are SMALL Not all viruses are bad for the host most are neutral some are Potential role in maintaining carbon and oxygen cycles of Classified into families each of which contains different genera Can be classified by the nature and organization of a virus s beneficial atmosphere genetic material Based on chemical composition Either RNA or DNA virus Enveloped Viruses Single stranded or double stranded genome Viruses that have additional lipid membrane surrounding the protein coat Kari Sanders 2 also called virus particles A virion refers to a physical particle Virions Resolution of a microscope whereas a virus is a more general term entities Bacteriophages viruses that infect bacterial cells ability to distinguish two objects as separate History Recognition of virus related disease trace back to 1500 B C Study of viruses did not start until the end of the 19th century It was after the final defeat of the spontaneous generation theory and the acceptance of the germ theory in the late 1800s o 3 pioneering scientists studying a disease called tobacco mosaic disease TMV Dmitri Ivanovsky Made the key argument that the infectious agent responsible for the disease was not bacterium but a new class of agents because it could pass through filter bacteria could not pass through Adolf Mayer Martinus Beijerinck 1898 the first animal virus was isolated foot and mouth disease virus Kari Sanders 3 The first human virus yellow fever virus was recognized at the turn of the 20th century 1930s structure of TMV had been solved by X ray crystallography o Electron microscope image of a virus had been obtained 1950s transition from classic virology to gene analysis of viruses o Started the development of molecular biology 1970s eradication of smallpox virus worldwide by vaccines 1980s discovery of the AIDS virus HIV Size ranges of molecules viruses bacteria and eukaryotic cells Micron 1 micron 1 micrometer o Bacteria and eukaryotic cells are in this range 10 100 micrometers Nanometer nm o Viruses are in this range 20 100 nm is the typical range of diameters for viruses Angstrom molecules are in this range o 1 nanometer 10 angstrom a virus with a diameter of 100nm is smaller than a virus with a diameter of 0 2 microns but larger than a virus with a diameter of 700 angstroms a filter with a pore size 0 2 microns will not trap a virus with a diameter of 150 nm What about a mimivirus that is 750 nm across o It will remove a mimivirus of 750 nm Kari Sanders 4 Virus Shapes Helical Or combinations of the two Icosahedron close to a sphere soccer ball 2 main types of microscopes o Either transmitted or scanning Different types of Electron Microscopy techniques o TEM Examines the cross section of biological samples o SEM scans the surface of biological structures Specialty EM o CryoEM Ultra low temperature and quick freezing to preserve the native unfixed structure of the virus o EM Tomography essentially the CT scan of viruses except the sample is tiled and the microscope is stationary A Light microscopes a Photons light is the source of energy b Can image living samples c Resolution 200 350 nm d Cant see viruses e Can see human cells and bacteria Kari Sanders 5 B Electron microscopes a Electrons is the source of energy b Cannot image living things because of the required vacuum c 100 times higher resolution 0 1 0 2 nm d Can see the interior structure of cells and the structure of viruses e Facts earth All the viruses on earth weigh 1000 times more than all the elephants on Kari Sanders 6 Most people are infected with 2 3 herpes viruses We all carry retroviral elements in our genomes o We carry in our cells small pieces of viral genetic information called retrotranspoons which are relics of ancient infection events Viral causes of common diseases Common cold rhinovirus Warts human papillomavirus Flu influenza virus 1 2 4 Cold sores herpes virus Diarrhea enterovirus Hepatitis HAV HBV HCB Small pox Variola virus AIDS HIV Poliomyelitis poliovirus Hemorrhagic fever Ebola dengue SARS coronavirus Terms bilayer at least once Transmembrane Protein outside Viral receptor entry into host cells Chapter Two Virus Entry a protein that spans across the membrane lipid o Serves as a barricade to separate the content of the cell from the a cell surface molecule that is bound by a virus to mediate its o Specific molecules on the host cell surface for binding o A virus may need multiple receptors to enter a cell o Receptors are host cell molecules that have normal functions for the cells but are hijacked by the virus to gain entry during an infection event Viruses hijack cellular resources host cells provide resources for majority of the tasks required for viral replication Viral genome packs information more efficiently o Part of receptors are facing the outside of the cell that interact with an incoming virion o The Importance of Studying Viral Receptors Kari Sanders 7 Elucidation of viral tropism Help predicting viral pathogenesis Revel drug targets for therapy Tropism types but not other the phenomenon that viruses are capable of infecting certain cell o The ability to infect a cell depends on the cell types permissive or non permissive surface Permissive cells display the correct viral receptors on their cell o Many viruses are also species specific meaning that it can only infect one species but not others The species barrier can be broken when a virus acquires mutations in its protein s that bind the receptor Endocytosis membrane bound vesicles called endosomes cellular uptake of materials from extracellular space using o Delivers a virus from the plasma membrane to endosomes o Normal function uptake of bulky materials from the outside of the cell o For this entry a drop of pH in the endosomes is usually required to trigger the fusion between the viral membrane with the endosome membranes This requirement of low pH prevents fusion of the viral membrane with the plasma membrane which is at a neutral pH Highly pathogenic avian influenza HPAI virus crossed over from waterfowl to
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