According to the current model, which of the following is the correct sequence of microtubule assembly?

oligomers, sheets of protofilaments, protofilaments, closing of microtubule, elongating microtubule dimers,

sheets of protofilaments, closing of microtubule, oligomers, protofilaments, elongating microtubule dimers,

oligomers, protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule dimers

protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule dimers,

oligomers, protofilaments, elongating microtubule dimers, sheets of protofilaments, closing of microtubule

oligomers, protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule dimers

Explanation:

Microtubules are polymers of tubulin and they are part of the cytoskeleton. The roles of the microtubules are to maintain the shape and structure of the cell, intracellular transport, they are structural part of the cilia an flagella, they are involved in cell division etc.

Tubulin that is the basic unit of microtubules is composed of two globular proteins, alpha and beta tubulin. Alpha and beta subunits sponta­neously form dimerswhich then assemble into oligomers, then in chains (protofilaments); that can form a variety of intermediate structures such as single and double rings or spirals. Protofilaments that associate side-by-side  form sheets of protofilaments which then curle to form a tube or cylinder (closing of microtubule). Continued growth of microtubules occurs by the di­rect addition of more dimers on + side.