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BCHM 2021 (1)
Chapter 14

Biochemistry- Chapter 14.docx

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BCHM 2021
Julie Clark

Biochemistry – Lecture14 -cytoskeleton  strength and shape and movement of cells -3 filaments: -intermediate filaments - mechanical strength - microtubules  intracellular transport, organelle location -actin filaments shape, locomotion -accessory protein control assembly -the regulation of these = helps build the cytoskeleton -motor proteins movement Actin filaments  also known as microfilaments -they are 5.9 nm thick -all eukaryotes -conserved -they form flexible filaments  form a network  bundles -these are generally found in the cortex  just beneath the plasma membrane Microtubules - all eukaryotes, conserved -25nm thick -rigid and hallow tubes -attached MTOC Intermediate Filaments -only in some metazoans some cell types -10nm thick -rope-like fibers that span across a cell -general principles of dynamics dynamic, constantly in flux assembled from small subunits -non-covalent interactions -rapid changes -accessory proteins control assembly and disassembly -small subunits protofilaments helical filaments -nucleation is rate-limiting -special nucleation proteins Microtubules -subunits= tubulin -globular, alpha and beta tubulin non-covalent binding -bind GTP -alpha-GTP never leaves -beta-GTP hydrolyze and exchanges - the protofilaments have alpha and beta alternating microtubules = 13 protofilaments -microtubules = 13 protofilaments -alpha = minus end and beta = plus end -this gives us polarity Actin Filaments -subunits =actin -one globular binds ATP -protofilaments  actin subunits = head to tail -filament = 2 protofilaments -polarity: plus and minus Polymerization -plus end = rapid addition of monomers -minus = slow addition -conformation changes -nucleotide hydrolysis  ATP or GTP hydrolyze after binding -the T form goes to the D form  this means that there is a lower affinity -the D form leaves -high monomer concentration  T form to plus and low concentration -T form to plus end -low concentration: D leaves -actin treadmilling  intermediate concentration -microtubles  dynamic instability -rapid shrinking for plus end  intermediate concentration **video 16.3 Microtubule_Dynamics** -Dynamic: requires a supply of energy  ATP/GTP hydrolysis exchange the ADP or GDP for a fresh ATP
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