BIOL 3510 1st Edition Lecture 21 Outline of Last Lecture I Enzyme coupled Receptors II Receptor Tyrosine Kinases III Intracellular Signaling Molecules IV Ras Mutated in Cancerous Cells V Plant Cell Communication Strategies Outline of Current Lecture I Three Main Cytoskeletal Filaments II Roles of Microtubules in a Cell III Microtubule Growth and Disassembly IV Motor Proteins Current Lecture Three Main Cytoskeletal Filaments Intermediate filaments IF subunit heterogenous family of fibrous proteins 10nm Microtubules MT subunit dimer of alpha and beta tubulin 25nm Microfilaments MF subunit activn 5 9 nm Intermediate filaments Ifs form stable networks that withstand mechanical stress Cytoplasmic IFs often connect to the plasma membrane at cell to cell junctions desmosomes Nuclear IFs nuclear lamins that assemble into a mesh that supports the nuclear envelope Intermediate filaments are assembled from a variety of proteins in different cell types and in the nucleus Fibrous proteins bind together and twist to form intermediate filaments In epidermal cells cytoplasmic IFs composed of keratins provide mechanical strength Plectins stabilize IFs and link them to other IFs microtubules and microfilaments Roles of microtubules in a cell A Cell organization and intracellular transport B Spindle assembly and function C Structural support of eukaryotic cilia and flagella These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Microtubules are stiff hollow tubes made of protofilaments composed of tubulin dimers Tubulin dimmers contain alpha tubulin minus end beta tubulin plus end In animal cells microtubules are nucleated from gamma tubulin complexes in centrosomes Microtubules are dynamic and grow and shrink rapidly dynamic instability Microtubule growth and disassembly Beta tubulin is a GTPase Only dimmers containing beta tubulin GTP is added to MT ends After dimer incorporation into a MT GTP is hydrolyzed to GDP causing a conformation change A cap of GTP tubulin favors microtubule growt The conformation of GGDP tubulin favors microtubule assembly If GTP hydrolysis proceeds faster than tubulin addition the GTP cap is lost and the microtubule disassembles In addition to the GTP cap microtubule dynamics are controlled by microtubule associated proteins MAPs The dynamic instability of microtubules is critical for microtubule function Selective stabilization of microtubules allows for cell organization and intracellular transport Intracellular transport is mediated by motor proteins The motor proteins kinesin and dynein move along MTs in opposite directions Kinesin moves to plus ends dynein to minus Movement is due to conformational changes powered by ATP hydrolysis They transport organelles and vesicles within a cell Motor proteins arrange the ER and Golgi apparatus Stable microtubules nucleated from basal bodies support cilia and flagella Cilia move fluid over the cell surface or propel cells Flagella propel sperm and protozoa MTs in cilia and flagella have a characteristic arrangement 9 2 Ciliary dynein coordinates cilia and flagella movement
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