Microtubules

Microtubules: Key Structures and Functions

• Microtubules are hollow tubes made of the protein tubulin, with a diameter of 25 nm and consisting of 13 protofilaments in its wall.
• They can be divided into stable (found in cilia, flagella, centrioles, and basal bodies) and labile (found in cytoplasmic microtubules and the mitotic spindle) microtubules.
• Microtubules are polar structures with fast-growing (+) ends and slow-growing (-) ends, important for determining the direction of movement along them.
• GTP plays a role in regulating microtubule polymerization, with GTP-bound dimers added to the plus end and hydrolyzed shortly after polymerization.
• Microtubules undergo dynamic instability, alternating between cycles of growth and shrinkage, regulated by Microtubule Associated Proteins (MAPs).
• Cytoplasmic microtubules play roles in intracellular transport, organelle stability, mitotic spindle formation, and cellular structure production.
• Drugs like colchicine, vincristine, and taxol bind to tubulin, affecting microtubule polymerization and spindle formation.
• Microtubule motor proteins, such as kinesin and dynein, transport cytoplasmic vesicles and are involved in ciliary movement, with ATP as a receptor for motor proteins.
• Kinesin and myosin head domains are structurally similar, and different tail sequences move different cargo types.
• Dynein, a 2000 kd protein, interacts with tubulin, moves along microtubules toward minus ends, and results in bending.
• The centrosome serves as the microtubule organizing center, determining the intracellular organization of microtubules and initiating their assembly.
• Centrosomes are located near the nucleus, play a significant role in microtubule assembly, and have a fundamental role in determining the intracellular organization of microtubules.