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Note Feb 4, 2013 recitation and lecture

Composition microfiliments f actin subunit is a

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Composition Microfiliments -f-actin: subunit is a protein known as G-actin (globulin) 42kDa- the most cytosolic protein Binds ATP/hydrolyzes. Cn either bind ATP or ADP It resembles cooked linguini Involved in cytokinesis, cellular crawling, muscle contraction F actin is 6nm Microtubules Largest (diameter wise): 25 nm, made of protein subunits called tubulin- this is made up of alpha, beta subunits which are tightly bound together by noncovalent bonds Resembles a drinking straw attached to a centromere Lots of protein protein interactions Protofilaments Tubulin: 55kDa Made up by tubular dimers, Always dimers, Binds GTP Built of globular subunits held together primarily by longitudinal bonds and the lateral bonds holding the protofilaments together is weak Break much more easily when bent than intermediate filaments do Alpha subunit( minus end) has GTP bound while the beta subunit ever has GDP or GTP bound(depends on which one it hydrolyzes), lateral contacts are between a-a and b-b. beta subunits are exposed to the plus end Ie- mitosis, mitotic spindle, allow internal movements, cell swimming Can form cilia and flagella on the surface of the cell or Ali bundles that serve as tracks for the transport materials down neuronal axons Intermediate filaments Line the inner face of the nuclear envelope to form a protective cage for the cells DNA 10nm in diameter 2 classes /ceil Nucleus- nuclear lamins Cytoplasmic- cell type specific- neurofilaments Subunit tetramer Asymmetric Lines the a side of the nuclear envelope to keep the Due to intermediate filaments. After the chromosomes have replicated, the interphase micro tubule array that spans throughout the cytoplasm is reconfigud into the bipolar mitotic spindle- accurately segregates the two copies of each replicated chromosome into two separate daughter nuclei
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nucleus strong Rigidity, resists pulling and pushing- rope like Ie- skin blistering diseases mutations found in the cytokerstin (a brush of a persons skin with this disease causes blistering) In epithelial cells: filaments hold epithetial sheets together Forms a mesh work called nuclear lamina just beneath the inner nuclear membrane Other types extend across the cytoplasm giving cells mechanical strength Polymer formation G-actin: at a good concentration to create a polymer Incubate it. And forms polymers in a test tube How to monitor polymer formation? Use an ultracentrifuge to find g/f- actin The polymer will pellet If you want a quick reputation if a polymer has formed then track the sample in real time Look at viscosity (how gel tlike it is! , turbidity(cloudiness) measure with spectrophotometer Critical concentration threshold Experiment:polymer formation over a period of time, one sample of actin in a test tube over time Actin grow by trying to get monomers together and increase their affinity for minor bending Trimmers-nucleus forms and then more minors can add onto both ends- rapid growth Once the solution has reached steady state, we want to dilute it and the concentration stays the same
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