Chapter 1 o Virology The study of viruses and its interactions with the host cells Began end of late 19th century 3 Pioneer Scientists on plant disease Tobacco Mosaic Disease 1 Dmitri Ivanovsky infectious agent responsible was not bacteria 2 Adolf Mayer est infectious nature of disease 3 Martinus Beijerinck proof agent was alive could multiply 1st animal virus foot and0mouth disease virus 1st human virus yellow fever o Why Study Viruses Not all viral infections manifest a negative effect in the host Study of viruses catalyzed the birth and growth of modern molecular biology Genomes viral genetic materials helped discover DNA Viruses can tell us how cells work Virus an obligatory intracellular parasite that carries a nucleic acid genome Enveloped viruses viruses that have additional lipid membrane surrounding o What is a Virus enclosed by protein coat the protein coat Virus is NOT a cell Virus genome carries limited info Virus lacks ability for metabolism it replicates inside a cell and cannot survive long outside host Viruses are small Average size human 1 2m chicken egg 5 10cm Need microscope to see them Resolution of a microscope ability to distinguish two objects as separate entities 1 Light Microscopes used to see changes in host cell photons 200 350nm 2 Electron Microscopes used to see viruses uses vacuum so cant see living samples electrons 1 2 nm EM Techniques TEM examines the cross section of biological samples SEM scans the surface of biological structures CryoEM ultra low temperature and quick freezing to preserve the native structure of the virus EM Tomography CT scan of viruses stays stationary o Come in Different Shapes Physical entity of a virus called a virion Consists of nucleic acid genome paged within a protein coat and may have lipid bilayer membrane envelope Usually symmetrical structures but vary greatly Rocket shaped bacterial virus rod like head filamentous tails Scientist use crystallography and X ray diffraction techniques to obtain more detailed info of the overall shape Knowledge of virion structure can facilitate efforts to produce anti viral drugs o Viruses Are Everywhere Infect organisms from all 3 domains Bacteriophages viruses that infect bacterial cells Extraordinary ability to persist in and coexist w their hosts leads to a distribution and abundance Tiny size explosive replications contribute to the astronomical number of viruses There are 10 31 32 on earth Everyone carries small pieces of viral genetic info called retro transposons relics of ancient infection events o Classifications and Names Viruses classified into singular genus genus have different species HIV 1 HIV 2 different members of the lentivirus genus part of the Family names ending in viridae refer to virus families names ending in retrovirus family virus represent viral genera Also classified by nature and organization of genetic materials DNA or RNA virus single or double stranded genome Baltimore classification Many pathogenic viruses named after symptoms or location of discovery or the scientists who discovered them Micron 1 micron 1micrometer bacterial eukaryotic cells are10 100 o Size Ranges microns Nanometer nm viruses 20 100 nm Angstrom molecules 1 nm 10angstrom o Viral Causes of Common Diseases Common Cold rhinovirus Flu influenza virus Warts human papillomavirus 1 2 4 Cold Sores herpes virus Diarrhea enterovirus AIDS HIV Poliomyelitis poliovirus Hemorrhagic Fever Ebola dengue SARS coronavirus Chapter 2 Virus Entry o Life Cycle Depend on host cells for survival Have extracellular phase when they spread Entry genome replication viral assembly exit Entry Structure of Biological Membranes Lipid bilayer with embedded transmembrane proteins Barrier that viruses must cross to deliver its genome into the cells Virus binding finds target latches to surface Use viral receptors specific molecules on host cells for binding May need multiple receptors to enter cell Permissive cells allow virus to infect display correct viral receptors Tropism phenomenon that viruses are capable of infecting certain Many viruses are species specific but can be broken if virus acquires cell types but not others mutations in its proteins Internalization penetrates cell membrane either direct pore formation or fusion Success of viral entry measured by delivery of viral genetic material inside the cell where it is utilized for protein expression Receptors host cell molecules w normal functions but hijacked by virus to gain entry entry into host cells Viral Receptors cell surface molecule bound by virus to mediate Transmembrane protein a protein that spans across the membrane lipid bilayer at least once Entry Receptors Can be Drug Targets Receptors can be targeted for inhibition when it comes to antiviral Host targeting strategy faces potential of cellular toxicity side therapy effects Entry Receptors and disease Implications Interaction between 2 proteins requires contacting surfaces to be compatible in shape and chemical properties Mutations that cause surface structure change can lead to change in interaction between virus and receptors Crossing Membrane Barrier Pore Formation Gap is opened by viral protein to allow part of virus to transport genome Fusion at endosomes Happens only with envelope viral membrane and cell fuse together that allows translocation of the viral core form the exterior to interior Either cross membrane at cell surface or penetrate membrane inside cells Endocytosis process that delivers a virus form the plasma membrane to endosomes Normal function uptake of bulky materials form outside the cell viruses use pH balance Highly pathogenic avian influenza virus avian flu virus that has crossed over from waterfowl to domestic birds and cause high rate of death in the latter population o General Steps of Virus Life Cycle Entry Replication Includes receptor binding all the way to membrane penetration Of viral genomes requires the expression of replication enzymes Viral Assembly and exit Requires the expression of replication enzymes o Importance of studying Viral receptors Elucidation of viral tropism Help predicting viral pathogens Reveal drug targets for therapy o 4 Possible Routes of Viral Entry 1 pore formation at cell surface neutral pH 2 Membrane fusion at cell surface neutral pH 3 Pore formation in the endosomes acidic pH 4 Membrane fusion in the endosomes acidic pH Chapter 3 Genome Replication o Must pass down genetic material genome in order to maintain identity 1st duplicated
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