Question

The number of protofilaments in a microtubule is
(a)10
(b)13
(c)16
(d)18

Answer 1

Hint Microtubules are part of the cytoskeleton of the cell which is responsible for maintaining the shape and structure of the cell and keeping the organelles in place. Microtubules are made up of protofilaments which are further made up of subunits known as tubulin.

Complete Answer:
Microtubules are long fibers of indefinite length found in the cytoplasm of the cell. Each microtubule has a dense wall with a hollow center. This dense wall of microtubules is made up of 13 protofilaments. The protofilaments are further made up of a subunit known as tubulin protein which is a dimer of alpha and beta-tubulin proteins. Thus, each protofilament is arranged parallel to the long axis of the microtubule and has alpha and beta-tubulin arranged alternately throughout its length. Proteins like dynein and kinesin are associated with microtubules.

Additional information:
Let us look at the functions of microtubules in detail.
Microtubules give rise to structures of cellular movement such as cilia and flagella.
Cell organelles were also formed by the special assemblies of microtubules such as basal bodies and centrioles.
Microtubules play a major role in cell division as they form the mitotic spindles which are responsible for organizing and separating chromosomes during cell division.
Microtubules are responsible for moving vesicles, granules, organelles like mitochondria and chromosomes.
Transportation and communication of molecules within the cells via microtubule “conveyor belts”.

So, the correct option is ‘13’.

Note: Since the tubulin protein is a dimer made up of two different kinds of subunits, it is known as a heterodimer. Along with microtubules, microfilaments and intermediate filaments make up the cytoskeleton of the cell. Centrioles form the basal body of the cilia or flagella or give rise to spindle fibers that form the spindle apparatus during cell division.