Unit 3 Viruses Human Disease Spring 2015 Unit 3 Viruses Human Disease BSC 1005 Dr Hengli Tang Chapter 1 Overview Know the Definition of a Virus What is a virus o An obligatory intracellular parasite that carries a nucleic acid genome enclosed by a protein coat Some viruses carry an additional lipid membrane Cannot survive outside the host cell Its genome carries limited information It lives a cushy life without doing much itself o Why Study Viruses o They scare us o They inform us AIDS swine flu Molecular technologies owe much of their origins to virology How cells function can be studied through virus studies Not all viruses are bad for their host Most are likely neutral some may o They sometimes help the host I Clicker Question even be beneficial o Which is the most serious threat to public health in your opinion common cold influenza Ebola carnival cruise virus Viral Diseases Ancient Records When were viruses discovered o Earliest records are an Egyptian stone tablet in 1500 BCE that depicts polio It was after the final defeat of the spontaneous generation theory and the acceptance of the germ theory in the late 1800s o o A Mayer M Beijerinck D Ivanovsky Mayer first established the infectious nature of the disease which is characterized by interspersing light and dark spots on the leaves of tobacco plants Ivanovsky made the key argument that the infectious agent responsible for the disease was not a bacterium rather a new class of agent because it could pass through the filters that had been used at the time to remove bacteria Beijerinck provided proof that the agent was alive and could multiply in living plants upon dilution ruling out the possibility that this was a chemical toxin All of these scientists demonstrated that a new class of transmissible agents was responsible for tobacco mosaic disease Later named Tobacco Mosaic Virus TMV Understand the relative size ranges of molecules viruses bacteria and eukaryotic cells as measured by the appropriate units Know the definition of Resolution of a Microscope Viruses are Small o A millimeter 10 3m o A micrometer 10 3 mm 10 6 m or 1 micron o A nanometer nm 10 3 micrometers o A nanometer 10 angstrom o One micron equals 10 000 angstroms I Clicker Question Light Microscope Unit 3 Viruses Human Disease Spring 2015 o Uses light as source of illumination o Can see human cells and bacteria o Can t see viruses o Resolution of a microscope ability to distinguish two objects as separate entities 200 350 nM Understand the difference between light microscopes and electron microscopes Fluorescent light microscopy can be used to detect infected cells Electron Microscopy o A comparison with light microscopy o 1 Uses electronic beams instead of light o 2 100 times higher resolution can see interior structures of the cells and o 3 Can only look at dead specimen because of vacuum requirement o 4 Complicated sample preparation steps In particular very thin slices of structure of viruses specimen are usually needed Select EM Techniques o TEM examines the cross section of biological samples o SEM scans the surface of biological structures o CryoEM Ultra low temperature and quick freezing to preserve the o EM Tomography essentially the CT scan of viruses except in this case the native unfixed structure of the virus sample is tilted the microscope scanner stays stationary Know the definition of a Virion Virions also called virus particles consist of an RNA or DNA genome packaged with a protein coat and in some cases a lipid envelope Know the viral causes of some common diseases Viruses come in all shapes but many are icosahedrons o Viruses need to use minimal number of proteins to make the virion o Closed shell made of identical subunits can only have limited types of Many viruses have additional lipid membrane surrounding the protein coat called the symmetry Tetrahedron Cube Icosahedron Know the definition of a enveloped virus enveloped virus Viruses weigh 1 000 times more than elephants o 1031 32 viruses on earth o All carry retroviral elements in genome o The Good Are All Viruses Bad Common cold and flu Small pox and AIDS o The Bad o The Ugly Sometimes a virus benefits an infected host Potential role in maintaining carbon and oxygen cycles of atmosphere Tools for research and medicine Know the definition of a bacteriophage Major scientific discoveries made me studying viruses o Vaccines protect from re infection o DNA not protein or sugar is the genetic material Bacteriophages also called phages for short are viruses that infect bacteria o Viral infections can cause cancer Unit 3 Viruses Human Disease Spring 2015 oncogenes good genes gone bad and tumor suppressor genes guarding angels of our genome o o Viruses can be modified to deliver medicine to treat genetic diseases Viruses are classified under family genus and species What s in a name o Disease symptoms o o Scientist who discovered the virus Location of discovery Chapter 2 The Life Cycle of a Virus I Entry Understand the general steps of a virus life cycle Virus entry is a multistep process with the ultimate goal of delivering viral genome payload into the cells Know the definition of a Transmembrane Protein Viral Receptor and Tropism Virions binding to cell surface receptors Understand the structure of biological membranes mediate its entry into host cells likely a transmembrane protein o A viral receptor is cell a cell surface molecule that is bound by a virus to The viral receptor is displayed on the cell surface for normal cell functions but hijack by the virus to latch on the cells lipid bilayer at least once A transmembrane protein is a protein that spans across the membrane The reason it is a lipid bilayer is because there is a hydrophilic water loving and hydrophobic water hating tails o A virus may need multiple receptors to enter a cell o The ability of viruses to infect certain cells but not others are typically due to the fact that only the permissive cells display the right viral receptors This is called the virus tropism Identification of HIV Receptors part I o Many viruses are species specific partially due to receptor differences o A cell surface molecule called CD4 is the primary receptor of HIV HIV only infects a subset of human T cells that express a cell surface HIV envelope protein binds to CD4 and blocking of this interact HIV Infection selectively depletes CD4 expressing T cells weakening molecule called CD4 prevents HIV entry the immune system o However mouse cells
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