MCB 150 Lecture 24: Week 7 - Topic 2-1

• School: University of Illinois
• Department: Molecular and Cell Biology
• Course: MCB 150
• Professor: B Mehrtens

Document Summary

Microtubules long, relatively rigid hollow tubes made of a globular protein tubulin dimer composed of 2 closely related 55 kda polypeptides -tubulin + -tubulin. Both - and -tubulin have nucleotide binding site bind gtp. Large compared to actin filaments spiral (have some stabilizing protein inside) Assembled head-to-tail microtubule has polarity (one end looks different than the other) minus end is usually occupied. Tubulin building block has polarity plus end and minus end in vivo assembly and disassembly fastest at plus end bc. Nucleotide in -tubulin is essentially hidden gtp hydrolysis happens @ -tubulin. Tubulin binds gtp gtp-bound tubulin has high affinity for plus end. Shortly after binding gtp in the -tubulin polypeptide is hydrolyzed. Gtp hydrolysis weakens affinity of tubulin for adjacent molecules favoring depolymerization. If concentration of gtp-bound tubulin is high, polymerization is favored. If concentration of gtp-bound tubulin is low, depolymerization is favored, (lost of gtp cap)