MICROFILAMENTS AND INTERMEDIATE FILAMENTS BY PRIANKA RAJAN Microfilaments
MICROFILAMENTS AND INTERMEDIATE FILAMENTS BY PRIANKA RAJAN
Microfilaments and intermediate filaments
CYTOSKELETOL COMPONENTS • THE MAJOR FILAMENTS RESPOSIBLE FOR MUSCLE MOVEMENT ARE ACTIN AND MYOSIN. • THE ACTIN AND CYTOSKELETON MACHINARY IS RESPONSIBLE FOR MAINTAINING CELL SHAPE AND GENERATING FORCE FOR MOVEMENTS. • POLYMERIZATION AND DEPOLYMERIZATION OF ACTIN FILAMENTS • 1. DRIVES THE MEMBRANE FORWARD. • 2. SUPPORT OVERALL CELL SHAPE.
ACTIN STRUCTURE • THE ACTIN CYTOSKELETON IS ORGANIZED INTO VARIOUS LARGE STRUCTURES THAT EXTEND THROUGHOUT THE CELL. • IT IS THE MOST ABUNDANT INTRACELLULAR PROTEIN IN MOST EUKARYOTIC CELLS. • IN MUSCLE CELLS ACTIN COMPRISES 10% WEIGHT OF THE TOTAL PROTEIN. • ACTIN EXISTS AS A GLOBULAR MONOMER CALLED G-ACTIN AND AS • A FILAMENTOUS POLYMER CALLED F-ACTIN. • EACH ACTIN MOLECULE CONTAINS A MAGNESIUM ION COMPLEXED • • ACTIN FILAMENTS ARE POLARIZED WITH ONE END AND CONTAINING AN EXPOSED ATP-BINDING SITE
MYOSIN • EIGHT MEBERS OF MYSOIN GENE FAMILY HAVE BEEN IDENTIFIED • MYOSIN I, II, AND V PRESENT EUKARYOTIC CELLS. MYOSIN VI, VII AND XV HAVE FUNCTIONS ASSOCIATED WITH HEARING AND HAIR CELL STRUCTURE. • INTERACTIONS BETWEEN MYOSIN II AND ACTIN FILAMENTS ARE RESPONSIBLE FOR MUSCLE CONTRACTION. • CELL MOVEMENTS OTHER THAN MUSCLE CONTRACTION AND CYTOKINESIS ARE BROUGHT ABOUT BY MYOSIN ISOFORMS – KENESIN OR DYNEIN OR BY ACTIN POLYMERIZATION. • THIS INCLUDES MOVEMENTS LIKE VESICLE TRANSPORT, MEMBRANE EXTENSION, CHROMOSOMAL MOVEMENT ETC. • ALL MYSOINS CONSIST OF ONE OR TWO HEAVY CHAINS AND SEVERAL LIGHT CHAINS THAT HAVE A REGULATORY FUNCTION.
CONTD…. . • A CHARACTERISTIC HEAD, NECK AND TAIL DOMAIN IS FOUND IN ALL MYOSIN HEAVY CHAINS. • ALL MYOSIN HEAD DOMAINS HAVE ATPase ACTIVITY AND IN CONJUCTION WITH THE NECK DOMAIN COUPLE ATP HYDROLYSIS FOR MUSCLE MOVEMENT.
MUSCLE CONTRACTIONS • IN SKELTOL CELLS, ACTIN THIN FILAMENTS AND MYOSIN THCIK FILAMENTS ARE ORGANIZED INTO HIGHLY ORDERED STRUCTURES CALLED SARCOMERES. • THE RAPID RISE IN CYTOSOLIC CALCIUM INDUCED BY NERVE STIMULATION OF A SKELTOL MUSCLE CHANGES THE INTERACTION BETWEEN ACTIN FILAMENTS AND TROPOMYOSIN, EXPOSING THE MYOSIN BINDING SITES AND THUS PERMITTING CONTRACTION TO OCCUR.
INTERMEDIATE FILAMENTS • INTERMEDIATE FILAMENTS ARE FOUND IN NEARLY ALL ANIMALS. • THEIR PRINCIPLE FUCNTION IS STRUCTURAL. THEY PROVIDE MECHANICAL SUPPORT FOR THE PLASMA MEMBRANE. • THEY DISTRIBUTE TENSILE FORCES ACROSS CELLS IN A TISSUE. • MAJOR DEGENREATIVE DISEASES OF SKIN, MUSCLE AND NEURONS ARE CAUSED BY DISRUPTION OF THE IF CYTOSKELETON.
ARRANGEMENT OF ACTIN
ATP BINDING TO ACTIN AND MYOSIN FIBRES
CONCLUSION • THE EUKARYOTIC CELL CONTAINS THREE TYPES OF FILAMENTS-ACTIN FILAMENTS(MICROFILAMENTS) , MICROTUBULES AND INTERMEDIATE FILAMENTS • THESE MAKE UP THE CYTOSKELKETON. • ACTIN AND MYOSIN ARE ORGANISED INTO HIGHLY ORDERED STRUCTURES CALLED SARCOMERES. • NERVOUS STIMULATION OF SKELETOL MUSCLES CHANGES THE INTERACTION BETWEEN ACTIN FILAMENTS AND TROPOMYOSIN , THUS EXPOSING THE MYOSIN BINDING SITES FOR CONTRACTION TO OCCUR. • INTERMEDIATE FILAMENTS PROVIDE MECHANICAL SUPPORT FOR THE PLASMA MEMBRANE
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