BIO SCI D103 Lecture Notes - Lecture 5: Microtubule Organizing Center, Spindle Apparatus, Nuclear Membrane
24 Jul 2019
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Document Summary
Many cells require rapid cytoskeletal rearrangements for normal function. Actin and microtubules: built from compact and globular subunits, subunits of actin and microtubules are asymmetrical and bind head-to-tail so they all pint in the same direction, gives filaments polarity along length, catalyze atp/gtp. Intermediate filaments: made from subunits that are elongated and fibrous, subunits are symmetrical and therefore not polar, don"t catalyze hydrolysis of nucleotides (atp/gtp) All 3 form helical assembles of subunits that self associate. Subunits make protofilaments (linear strings of subunits joined end-to-end) that associate with one another laterally to form a follow sphere: less easy to break but still flexible. Actin has a slower growing (-) end and a faster growing (+) end. For filaments to form, subunits must assemble into an initial aggregate (or nucleus) stabilized by multiple subunit contacts and can then elongate rapidly by addition of more subunits. Instability of small actin aggregates creates kinetic barrier to nucleation.
