D103 - Lecture 7 - Microtubules.docx

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Department
Biological Sciences
Course
BIO SCI D103
Professor
Grant Mac Gregor
Semester
Winter

Description
A.Microtubule a. Alpha and beta tubulin i. Are not found free in the cytosol ii. Always need to be a dimer b. Alpha tubulin i. GTP is bound- never hydrolyzed b. Beta tubulin i. GTP bound here can be hydrolyzed to GDP b. 13 polar protofilaments form a microtubule c. GTP on beta tubulin is hydrolyzed slowly i. GTP cap 1. The alpha/beta dimers are still bound to GTP at the + end 2. Adding too fast 3. Needed for the microtubule to extend 4. NOT A CAPPING PROTEIN ii. GDP cap 1. Microtubule will depolymerize 2. Individual protofilaments are falling apart B.MT binding proteins a. Stathmin i. Sequestering protein, binds subunits b. Kinesin 13 i. Enhances disassembly at the plus end ii. Catastrophe - disassembly b. Gamma-TuRC i. Related to tubulin ii. Nucleation factor at the minus end 1. Serves as a cap at the minus end b. XMAP215 i. Stabilizes plus end and accelerates assembly B.Microtubule Organizing Center (MTOC) a. Centrosome b. Nucleates and anchors MT at the minus end c. Gamma-tubulin is localized here B.Centrosome a. Centrioles are organized in triplets, 9 triplets b. Centrioles i. Not present in plants or fungi b. Gamma-tubulin = part of the gamma-TuRC proteins c. No branching d. JOB i. Interphase 1. Helps with cell polarity, organelle position, vesicle transport ii. Mitosis 1. Forms the bipolar mitotic spindle B.Centrosomes duplicated a. Centrosomes are duplicated once per cell cycle i. Duplica
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