ImmunoglobulinsScan pp. 221-228 for background, but you are not responsible for this material.You are responsible for the material on antibodies, pp. 228-233,and the rest of the chapter.Focus on protein-ligand bindingat the molecular level and analytical techniques using antibodies (figure 7-28, p. 232). Structure of IgGAntibodies - produced and secreted by B lymphocytes-make up 20% of blood protein- each antibody recognizes a specific antigen-An antigen may be a virus, a bacterial cell wall, a particular protein or other macromolecule-An individual antibody binds only a particularmolecular structure within the antigen- called the epitope-Can bind to Fc receptors on macrophages, triggeringphagocytosis of antibody-antigen complexHost Cell is lysed by virusSoluble antibodies canbind virus and directthem to macrophagesto be destroyedImmunoglobulin G, IgG,the major class of antibody molecule and one of the most abundant proteins in the blood serum.4 polypeptide chains (2 heavy+ 2 light chains)Mr150,000Fragment that usually crystallizesAntigen-binding fragmentRibbon model of first complete IgGcrystal structureBinding of IgG to an antigen“Induced fit”: The binding sites of IgG often undergo slight conformational changes as they bind. Common to many protein-ligand interactions.IgM pentmer-The major antibodyin early stages ofprimary immuneresponsePhagocytosis of an antibody-bound virus by a macrophage. The Fc regions of the antibodies bind to Fc receptors on the surface of macrophage, triggering it to engulf and destroy virusInduced fit of binding of antigen to IgGAntibody TechniquesELISA assay ImmunoblotEnzyme-linked immunosorbent assay•adsorb sample on polystyrene plate•block empty sites with inert protein•treat with primary antibody, then wash•treat with secondary antibody-enzyme complex, then wash •Add substrate of enzyme contained in secondary antibody•separate sample using gel electrophoresis•transfer proteins electrophoretically to nitrocellulose membrane•block empty sites with inert protein•treat with primary antibody, then wash•treat with secondary antibody-enzyme complex, then wash •add substrate of enzyme contained in secondary antibodyStructure of Skeletal MuscleZ-diskYou are responsible for the material on pp. 233-239.Electron Micrographs of MusclerelaxedcontractedThick filaments are myosin aggregatesThin filaments are made up of actinMuscle contractionRelaxed--> ContractedSliding of thick and thin filamentspast each other so that theZ disks in neighboring I bandsapproach each otherEach thick filament issurrounded by sixthin filamentsMyosinLight chains are blueMyosinHeavy chains are dark and light pinkStructure of myosin headLight chainsHeavy
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