Lecture 8: The Dynamic Cytoskeleton
Lecture 8: The Dynamic Cytoskeleton 200001
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This 8 page Class Notes was uploaded by Olivia Sutton on Sunday March 20, 2016. The Class Notes belongs to 200001 at Boston College taught by Danielle Taghian in Spring 2016. Since its upload, it has received 7 views. For similar materials see Molecules and Cells in Biology at Boston College.
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Date Created: 03/20/16
Lecture 8: The Dynamic Cytoskeleton February 22, 2016 The Dynamic Cytoskeleton The cytoskeleton is a complex network of fibers that helps maintain cell shape by providing structural support Acts like a transportation highway of the cell Function o Alters the cell’s shape o Transports materials in the cell o Move the cell itself 3 Types of Elements o Actin filaments (red) Linear polymers of globular actin (G-actin) subunits Occurs as microfilaments in the cytoskeleton Are thin filaments that are part of the contractile apparatus in muscle and non-muscle cells o Intermediate filaments Added components to the cytoskeleton o Microtubules (green) Appears to have some order/polarity to them Are secretory cells Function: transports protein Cells have polarity If cells were treated with colchicine (one of the most toxic drugs), the golgi dissolves away and microtubules are depolarized. However, when you wash away colchicine, the microtubules reform. However, colchicine targets EVERY cell besides tumor cells (why people get very sick) Microtubules Large, hollow tubes made of tublin dimers (2-part compounds) Have polarity and are dynamic (grow & shrink) Usually grow at their plus ends Function o Provides stability o Involved in movement o Provide structural framework for organelles and a track for intracellular transport Most common arrangement is a singlet (sometimes there is a doublet arrangement Are the largest elements in the cytoskeleton Originate from the microtubule organizing center and grow outward, radiating through the cell Animal cells have one microtubule-organizing center called the centrosome. o Contain tow bundles of microtubules called centrioles. Organizing center is right next to the nucleus During cell division, microtubules move chromosomes from the original cell to the resulting cell o Microtubules depolarize as they pull the chromosomes to the individual microtubule-organizing centers Peroxisomes appear to be localized with microtubules Because microtubules act as “railroad tracks” for cells, vesicles travel through the cell through the microtubule tracks o This process requires ATP! Taxol Drug used to treat solid cancers; very effective but has side effects Purified from the Pacific yew tree (but its an endangered species though it was the only way to get it Binds to beta-site of tubulin and stabilizes the microtubules o Prevents them from being dynamic (can’t depolarize) o That’s how cell proliferation is blocked Motor Proteins Move vesicles along microtubules Microtubules require ATP and kinesin for vesicle transport to occur Kenesin motor protein converts the chemical energy in ATP into mechanical work (movement) o Literally walk across microtubule track towards the positive end (towards the membrane) They are so large that they can be seen with a microscope. The two heads segments of kinesin act like feet that attach/release when bound by ATP analogous to a delivery truck The cell has different motors that are associated with different vesicles Cilia and Flagella Flagella: long, hairlike projections from the cell surface that move cells o Bacterial flagella: made of flagellin and rotate like a propeller o Eukaryotic flagella: made of microtubules Cilia: closely related eukaryotic flagella; short, filament-like projections Actin filaments Smallest cytoskeletal elements Form by polymerization of individual actin molecules Can grow and shrink as actin subunits are added or subtracted from each end Grouped together into long bundles or dense networks Usually found inside plasma membrane to help define cell chape Similar structure of a double helix for added strength Moves cells via muscle contraction or cell crawling Helps in cell division Look like rope Actin-Myosin Interactions Can also be involved in movement by interacting with the motor protein myosin When myosin’s head attaches to the actin and moves, the actin filament slides Produces several types of movement: o Cell crawling: actin polymerization creates pseudopodia that extend and move cell o Cytokinesis: cell division; pinch membrane in two o Cytoplasmic streaming: cytoplasm moves around the cell Intermediate filaments Defined by size instead of composition Many types exist Medium sized element in cytoskeleton More tightly twisted rope Provide structural support for the cell o Not involved with movement