BIOL 200 Chapter Notes - Chapter 6: Axoneme, Molecular Motor, Cilium
Document Summary
Important organizing role in the cell, responsible for: Position of many organelles (especially in mammalian cells) Maintenance of cell shape (especially in plants, fungi and protists) Composed of a ring of 13 protofilaments. Each protofilament: composed of dimers of alpha-tubulin and beta-tubulin. Positions of tubulin dimers in adjacent protofilaments is slightly out of phase form spiral. Grow by addition of new monomers to end of existing microtubule. Subunits have uniform polarity arranged into 2 different ends. Addition of tubulin dimers is fast at one end than the other. Result in growth at one end more than the other. Note: plus/minus ends have nothing to do with charge or electrical polarity. Occurs through the use of a nucleation center. Initiation is difficult if small amounts of very short microtubules are added, long microtubules are quickly formed through a crystallization-like process. Contain rings of a special tubulin monomer (gamma-tubulin) that forms the nucleating sites.
