BIOL 3510 1st Edition Lecture 21 Outline of Last Lecture I. Enzyme-coupled ReceptorsII. Receptor Tyrosine KinasesIII. Intracellular Signaling MoleculesIV. Ras Mutated in Cancerous CellsV. Plant Cell Communication StrategiesOutline of Current Lecture I. Three Main Cytoskeletal FilamentsII. Roles of Microtubules in a CellIII. Microtubule Growth and DisassemblyIV. Motor Proteins Current LectureThree 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 transportB. Spindle assembly and functionC. Structural support of eukaryotic cilia and flagellaThese 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 changeA “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 microtubuledisassembles. 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. Intracellulartransport 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
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