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Biology 1001A
Tom Haffie

Lecture 3 Cell Biology The cytoskeleton Supports and Moves cell structure y Shape and internal organization of each type of cell are maintained in part by its cytoskeleton the interconnected system of protein fibres and tubes that extends throughout the cytoplasmy The cytoskeleton also reinforces the plasma membrane and functions in movementboth of structures within the cell and of the cell as whole y Animal cells contain three major types of structural elements microtubulesintermediate filamentsand microfilaments Plant cytoskeletons contain only microtubules and microfilaments Microtubules are microscopic hollow tubes Intermediate filaments are fibres that occur singly in parallel bundles either alone or in combination with microtubule microfilamentsor both Microfilaments are thin fibres that consist of two rows of protein subunits wound around each other in a long spiraly Motor proteins that push or pull along microtubules or microfilamentsOne end of a motor protein is firmly fixed to a cell structure such as a vesiclea microtubuleor a microfilaments The other end has reactive groups that walk along another microtubule or microfilament by making an attachment forcefully swivelling a short distanceand then releasingATP supplies the energyFigure 222 The major components of the cytoskeleton as visualized by specific staining and light microscopy TOP and molecular models BOTTOM a Microtubules are stained yellow in a pancreatic cell Microtubules are assembled from individual tubulin subunits b Intermediate filaments assembled from keratin proteins in cells of the kangaroo rat The nucleus is stained blue in these cells In intermediate filaments eight protein chains wind together to form each subunit shown as a green cylinder c Microfilaments red in a migrating mammalian cell A microfilament is assembled from two rows of actin proteinswound around each other into a double helixDouble helical structure of DNA with two antiparallel backbones1
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