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Section 4 Intermediate Filaments.docx

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Western University
Biology 2382B
Robert Cumming

Intermediate FilamentsIntermediate filaments arent globular No ATP or GTP neededno polarity no known motor proteins Most important thing is that intermediate filaments are important for structural aspects of cellthey have strong tensiles strength Atin cytoskeleton is usually cortical can be involved in things like cell migrationMicrotbules are found coming from a centrosome and are for ortganelle transportWhereas intermediate filametns are involved in integrityholding things in place and providing strength in tissues GREAT TENSILE STRENGTHif you pull on it they will not riMain types of Intermediate FilamentsDifferent intermediate fliamentts are found exclusively in different cells and can be used to determine what cels are Mosymtomal cellspoorly differentiated migrated cello A fibroblast for example is a mosymbtemol cello Poorly differentiated means that It can form different things not quite a stem cell but has some leeway in what it can beo VIMENTIN is used in these cells to migrate NeurofilametnsNFL NFM NFH light medium and heavy filamentso If you see NFL you know its a nerve cell The exception here is laminthis is found in most cellssupport the nuclear membraneIt is found in most cells and supports the nuclear membrane Keratin is what makes your skin cellsas your skin cells are being producedeventually you get a huge cell of keratinzed skin cellsthe skin cells at the top are empty cells and just kertain this is the intermediate filament Thats the same intermediate filamentMost of theseare used in structural elements Intermediate filaments o Have no polarityo Are not globular o Dont need energy to polymerize Building blocks of intermediate filaments are relatively large proteinsthey have head rod and tail domains Intermediate filamentsStructureComposed of a dimer 1 Head Section 2 Rod Section 3 Tail SectionHas an N and a C terminus the Cterminus is the tailTwo of these come together to form a tetramer this is the basic unit This is what polymerizes into intermediate filaments The TETRAMER is the basic building blockBecause of the way the dimers come together to form the tetramer the tetramer has no polaritythe tail domains are on both ends it doesnt matter what domain is on the end though what matters is that the ends show no difference flipping it 180degrees will show no differenceMade up of relatively large proteinsThese tetramers come together spontaneously dont require energy to form protofilamentsMade up of relatively large subunitsnot globular The polymerization doesnt require energy no atp or gtpTETRAMERS COME TOGETHER TO FORM INTERMEDIATE FILAMENT THATS WHATS RELAVENT It does polymerize and depolymerizeit is dynamicNot as dynamic as actin and tubulin but can be poyermized and depolymerizedThis can be seen because the subunits within intermediate filemtns can be exchangedcan be added or removed You can check thisyou can label keratin with biotin and add that too the celleventually you see the biotinated keratin in little spots those subunits drift randomly in the cytoplasm but over time it eventually gets incorporated into the intermediate filaments All the intermediate filaments have this biotinated keratin nowit was incorporated into the existing intermediate filament It can incorporate new subunits into existing structuresWhen the cell changes all the different cytoskeleton elements will need to change shape to conform with the changes that the overall cell is undergoing Laminshelp to disassemble the intermediate filamentsThere are different kinds of laminslooking at specifically Lamin Athese are found in the nucleuso To take it apart removing the Lamin Athis is done through phosphorylation o There is a specific serine residue on that lamino When the serine residue is phosphorylated this induces disassembly and prevents reassemblyo As long as the serine residue is phosphorylated you cant polymerize the nucleus but instead depolymerizeo If you get rid of the serine residue it cannot diassemble the nuclear membrane which will lead to an inability to replicate the cello During mitosis for example it is the working together of kinases and phosphatases that allows for that assemblydisassemblyPhosphatase will remove the phosphate group and allow for assembly to occur
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