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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