Lecture 1 Introduction A Virus Is an intracellular parasite that carries a nucleic acid genome enclosed by a protein coat Its nucleic acid genome carries limited information They cannot survive outside the host cell They need us to reproduce and live Many are enveloped viruses which means they have additional lipid membranes surrounding the protein coat Viruses are very TINY A micrometer mm 10 3 mm 10 6 Units m A micrometer mm 1 micron A nanometer nm 10 3 mm A nanometer nm 10 angstroms e y e n a m u h d e k a N Human Chicken egg Frog eggs e p o c s o r c i m t h g i L e p o c s o r c i m n o r t c e l E Eukaryotic cell Bacteria Virus es DNA Atoms Micron Bacterial and eukaryotic cells A filter with 0 2 micron size pores effectively remove bacterial contamination Nanometer Viruses Angstroms Molecules 1 Light Microscope Because viruses are so small they can only bee seen with microscopes There are 2 different types of microscopes Uses light as source of illumination uses photons Can see human cells and bacteria Can t see viruses 2 Electron Microscope Uses electronic beams instead of lights Much higher resolution to be able to see inside cells Can see viruses There are 4 different techniques of Electron Microscopes I II III IV TEM views the cross section of samples SEM Scans the surface of samples CryoEM Uses ultra low temperature to preserve and view the virus EM Tomograph Views virus in a stationary scanner while titling the sample Determining Virion structure a Virions also called virus particles consist of RNA or DNA genome packaged within a protein coat and in some cases a lipid envelope i Viruses come in all shapes but many are icosahedrons Viruses need to use minimal number of proteins to make the virion Closed shells made of identical subunits can have limited types of symmetry Viruses have a membrane Many viruses have additional lipid membranes surrounding the interio Be sure to know the different disease and their viral counterpart Common Disease Common cold Flu Warts Cold Sores Diarrhea AIDS Poliomyelitis Hemorrhagic fever SARS Viral Cause rhinovirus influenza virus human papillomavirus 1 2 4 herpes virus Enterovirus HIV Poliovirus Ebola Dengue coronavirus Lecture 1 Definitions Virus an obligatory intracellular parasite that carry a nucleic acid genome enclosed by a protein coat Enveloped viruses viruses that have additional lipid membrane surrounding the protein coat Virions also called virus particles A virion refers to a physical particle whereas a virus is more general term Resolution of a microscope ability to distinguish two objects as separate entities Bacteriophages viruses that infect bacterial cells Lecture 1 iClickers One micron equals A 1 B 10 C 100 D 1000 E 10 000 Answer E Lecture 2 Entry The general steps of a virus life cycle The first step the virus binds to a receptor entry and uncoating early gene expression replication of viral genome late gene expression assembly of viral progeny exit 1 Binding to viral receptor The virus binds to the cell surface receptors A viral receptor is on the surface of our cells typically a transmembrane protein Viruses need multiple receptors in order to enter a cell Viruses have the ability of trophism This means a virus can attack certain cells that display the right vital receptors If it does not show the right vital receptors than it cannot infect it Only permissive cells display these correct viral receptors I If the virus is a non enveloped virus It will enter the cell by Pore formation II If the virus is a enveloped virus it will enter the cell by Membrane fusion Cell membrane structure and hydrophobicity transmembrane protein a protein that span across the membrane lipid bilayer at least once lipid bilayer made of lipids Arranged head to tail because they are hydrophobic Viruses must cross this barrier to deliver its genome into the cells Lipid Bilayer The dark brown odd shaped rectangles are transmembrane protein spanning across the lipid bilayer Understand the importance of studying viral receptors a Viral tropism refers to The fact that the virus an affect certain cell types 1 Elucidation of viral tropism but not others 2 Help predicting of viral pathogenesis 3 Reveal drug targets for therapy Membrane penetration by viruses employs two basic strategies pore formation and membrane fusion Entry via Membrane Fusion enveloped viruses In this case viral receptors attach to the receptors on the surface of the cell and secondary receptors may be present to initiate the puncture of the cell membrane or fusion with the host cell followed by the unfolding of the viral envelope In essence the virus s envelope blends with the cell membrane releasing its contents into the cell Obviously this can only be done with viruses that contain an envelope Entry via Endocytosis pH dependent aka Pore Formation non enveloped viruses Another example is the triggered endocytosis of a cell in which the virus tricks the cell into thinking that the virus knocking at the door is nothing more than nutrition or harmless goods A cell naturally takes in resources from the environment and one of the ways it does so is by attaching goods onto surface receptors and engulfing them into the cell Once inside the cell within the vacuole by which it was taken up the virus must now break out of the vacuole to gain access to the cytoplasm Basic Overview Viruses bind to cell surface receptors Neutral pH Viruses bind in the endosome by means of endocytosis acidic pH Lecture 2 Definitions Transmembrane protein a protein that spans across the membrane lipid bilayer at least once Viral receptor a cell surface molecule that is bound by a virus to mediate its entry into host cells Tropism the phenomenon that viruses are capable of infecting certain cell types but not others Endocytosis cellular uptake of materials from extracellular space using membrane bound vesicles called endosomes Highly pathogenic avian influenza HPAI virus Avian flu virus that has crossed over from waterfowl to domestic birds and causes high rate of death in the latter population Lecture 2 iClickers 1 Which of the following is a possible route of virus entry a Formation at the cell surface b Pore formation at the endosome membrane c Membrane fusion in the endosome d Membrane fusion at the cell surface Answer all of the above Viral tropism refers to Answer The fact that the virus an affect certain cell types but not others Lecture 3 Replication Viral genomes are only examples of RNA based
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