BIOL2200 Lecture Notes - Lecture 6: Atp Hydrolysis, Axoneme, Dynein
CYTOSKELETON LEC 3 BIOL2200
Lecture 3: microtubules and intermediate filaments
Microtubules
Long tubular structures that they called microtubules. Transverse sections showed that they
were composed of 13 repeating units: protofilaments
Purified microtubules were found to be composed of a protein tubulin
Microtubules are one of the components of the cytoskeleton
They have diameter of ~24nm length varying from several micrometres to possible
millimetres in axons of nerve cells
Microtubules serve as structural components within cells and are involved in many cellular
processes including mitosis, cytokinesis, and vesicular transport
They are formed of hetero-dimers of a alpha-tubulin and beta-tubulin
Tubulin extensive array of microtubules
Globular protein 55kDa
Microtubules are assembled from dimers of alpha- and beta-tubulin
Microtubules consist of 13 laterally associated protofilaments forming a tubule of 25nm
Subunits alternate down each protofilament
Other family member: gamma-tubulin: nucleation and polar orientation of microtubules
Microtubule assembly
Microtubules are assembled at specific sites: microtubule organising centres - MTOC
MTOC also called the centrosome in nonmitotic cells
Comprised of specialised microtubules
MTOC anchors to (-) end of microtubule
MTOC located near the nucleus and extend
MTOC located near the nucleus and extend radical arrays of microtubules
MTOC in dividing cells
During mitosis cells completely reassemble their microtubules to form a bipolar spindle
Spindle assembles from two MTOCs called spindle poles
Microtubule dynamics
Alpha/beta-tubulin dimers bind GTP and assemble onto the (+) ends of microtubules
After dimer is incorporated into the microtubule, GTP is hydrolysed to GDP (beta-subunit).
The GTP cycle is essential for the dynamic instability of the microtubule
Thus microtubules treadmill (like microfilaments)
Microtubules as transport structures
Organelles is cells are transported long distances
Cargo vesicles can be:
oTransported toward the (+) end or cell periphery (anterograde) or
oTransported from the periphery to the cell body toward the (-) end (retrograde)
Classic example: axonal transport in neurones
Concept of microtubules as molecular motors
Microtubule motors
Two molecules mediate transport:
oKinesin for anterograde
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Long tubular structures that they called microtubules. Transverse sections showed that they were composed of 13 repeating units: protofilaments. Purified microtubules were found to be composed of a protein tubulin. Microtubules are one of the components of the cytoskeleton. They have diameter of ~24nm length varying from several micrometres to possible millimetres in axons of nerve cells. Microtubules serve as structural components within cells and are involved in many cellular processes including mitosis, cytokinesis, and vesicular transport. They are formed of hetero-dimers of a alpha-tubulin and beta-tubulin. Microtubules are assembled from dimers of alpha- and beta-tubulin. Microtubules consist of 13 laterally associated protofilaments forming a tubule of 25nm. Other family member: gamma-tubulin: nucleation and polar orientation of microtubules. Microtubules are assembled at specific sites: microtubule organising centres - mtoc. Mtoc also called the centrosome in nonmitotic cells. Mtoc anchors to (-) end of microtubule. Mtoc located near the nucleus and extend.
