Final answer:
Microtubules are hollow structures made from α-tubulin and β-tubulin dimers that form part of the cytoskeleton. They have structural polarity and play key roles in cell rigidity, intracellular transport, and cell division. Cilia, flagella, and centrioles contain microtubule doublets or triplets, illustrating the variety in microtubule structure.
Step-by-step explanation:
Understanding Microtubule Structure
Microtubules are fundamental components of the cytoskeleton in eukaryotic cells. They are small hollow tubes with diameters of about 25 nm. Each microtubule is made from polymerized dimers of two globular proteins, α-tubulin and β-tubulin. Thirteen of these dimers polymerize side by side to form a sheet that rolls into a tube, creating a single microtubule, or a singlet. Structures such as cilia and flagella consist of microtubule doublets, in which one microtubule is shared between two structures, or triplets as in centrioles.
Each tubulin dimer has an orientation, with the α-tubulin exposed at the minus end and β-tubulin exposed at the plus end, giving the microtubule structural polarity. This polarity is essential for their functions, such as provinding tracks for motor proteins like dynein and kinesin, helping resist cell compression, facilitating vesicle transport, and segregating chromosomes during cell division. Mircofilaments, made primarily of actin, and intermediate filaments, which include keratin, are other components of the cytoskeletal network.