Note Feb 4, 2013 recitation and lecture

The actin nucleotide is atp or adp not gtp or gd

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The actin nucleotide is ATP or ADP, not GTP or GD Actin filaments consist of two parallel protofilaments that twist around each other in a rig handed helix Experiment 2: vary the concentration The more dilute a solution is, the less the polymer to the point of no polymer Less concentration, less polymers Ginger concentration, higher polymers Actin filaments : 2 stranded helical polymers of the protein actin, highly concentrated to the cortex, just beneath the plasma membrane provide strength and shape to its thin lipid bilayer Actin structures that also enable fibroblasts to crawl across the cell surface, form a belt, with the help of other motor proteins, or a contractile ring to separate the cell into two Apical surface: absorbs nutrients from the lumen of the intestine where food passes by to the basolateral surface where the cells transfer nutrients through the plasma membrane to the bloodstream Polarized orientation of the actin structures influences the orientation of the mitotic spindle
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Protein molecules of the cytoskeleton are small and diffuse quickly within the cytoplasm where's filaments cannot Covalent linkages hold the subunits together (actin to actin filaments and tubulin subunits to microtubules) Including DNA RNA and proteins. Weak non covalent bonds hold together the cytoskeletons polymers Cytoskeleton polymer,s combine to make protofilaments- long linear strings of subunits joined end to end They twist around one another to form a helical lattice Resist thermal breakage, while leaving the filament ends as dynamic structures at which the addition and,OSS of subunits can occur rapidly February 6th, 2013 Filament polarity '+' end- more rapid filament growth and disassembly '-' end- Relative rates of assembly/disassembly Two things that allow filaments to have this assembly Building block asymmetric One end will look different on one end then another- different subunits Motor proteins Ability to hydrolyze nucleotides ATP is not necessary for self- assembly How to distinguish the two ends of the filament? Electron microscopy!!
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Minus end has slower dynamics and a higher critical concentration- need more subunits to get them to stick on the minus end. Not as appealing to bind on the minus end. Tubulin protomer How did we figure this out? -use a frozen EM technique Cryo-EM Cells are frozen in liquid helium- left with vitreous ice( unstructured ice) this happens because its frozen so quickly With microtubules, once they start disassembling they can't stop and it becomes dynamic instability Growths to shrinkage-catastrophe Shrinkage to growth- rescue Can use fluorescence, DIC/ nomarski/ light microscopy to detect the growth of microtubules E light microsce can only go to 200nm so this can be seen but the resolution isn't great
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Cell Biology (020.306) CYTOSKELETON Weeks 2 and 3 1 Introduction to the cytoskeleton The cytoskeleton is a set of non-covalent protein polymers (filaments) and the proteins that bind to them. These proteins determine a cell's shape and provide the basis for cell movement and division.
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