NE102 Lecture Notes 2

Cells build microtubules at specialized center called

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Cells build microtubules at specialized center called “ centrosomes Centrosomes build microtubules from the – end to the + end  Dimers at the + end are GTP-bound. MTs grow by the addition of the GTP – bound dimers to the + end = GTP cap GTP cap stabilizes the MT GTP is hydrolyzed to GDP soon after being added.  MTs shrink at the + end in the absence of a GTP cap. Centrosomes are located near the center of interphase cells (adjacent to nucleus) The – ends of MTs are anchored at centrosomes & extend outward to the periphery of  the cells.  Once assembled, microtubules can be released from the centrosome to organize  elsewhere in the cell.  Ex.) MTs in axons & dendrites of neurons.  Microtubules are dynamic within cells. MT assembly and disassembly is regulated by  microtubule-associated proteins (aka,  MAPs) Bind & stabilize MTs Sever the middle of MTs Modulate rates of assembly/disassembly
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Cytoskeleton and Motor Proteins 19:00 Direct the localization & orientation of MTs Ex.) Tau = neuronal MAP involved in the pathology of several neurodegenerative  diseases (e.g., Alzheimer’s Disease) Tau normally binds & regulates MT stability in neurons QUESTION: What roles do microtubules play within cells? 1. Microtubule organization affects cell structure.  2. Microtubules play a key role in chromosome segregation during cell division  (i.e., mitosis) 3. Facilitate the transport of vesicles & organelles within cells.  ROLE #3 of MTs HOW? MTs provide “tracks” along which “motor proteins” transport cargo. Motor proteins  = proteins that bind MTs & “cargo” and carry out intracellular transport Two families of motor proteins: (1) Dynein & (2) Kinesin Two functional domains Head domain = motor domain Bind MTs & ATP Couple ATP hydrolysis to walk along MTs Tail domain = cargo domain Bind specific cargo & mediates its transport along the MT Dynein & kinesin transport cargo in specific directions along microtubules Dyneins walk towards – end
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Cytoskeleton and Motor Proteins 19:00 Kinesins walk towards + end ACTIN FILAMENTS Polymers of actin monomers, called  G actin Two ends: barbed end & pointed end Pointed end connects to barbed end Assembly begins with nucleation Trimer forms Growth at both ends  Results in actin filament ( F actin ) with distinct polarity Actin filaments underlie the plasma membrane to provide structure.  Actin filaments are anchored ot the plasma membrane via protein-protein interactions  with transmembrane & adaptor proteins Actin filaments are organized in actin  bundles  &  networks  by  cross-linking proteins.
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Cell Division  Guest Lecture: Lucia Pastorino 19:00 Topics:
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