Question

What is the role of microfilaments in cytokinesis?

Answer 1

Hint: Microfilaments are one among the cytoskeleton of the eukaryotic cell. It is a double-stranded helical biopolymer of fibrous actin, which is formed from the monomeric units of globular actin proteins. Both F (fibrous) and G (globular) actins exist in dynamic equilibrium within the cell.

Complete answer:
Actin filaments or microfilaments are polar in nature, and they have a minus-end (referred to as “pointed”) and a plus end (referred to as “barbed”). New G-actin monomers are added to the growing plus end, and after addition to the filament, the ATP in G protein hydrolyzes to ADP. The process of addition of monomers continuously at the plus end and removal of monomers from the minus end is known as treadmilling.
Microfilament participates in many crucial cellular processes such as cytokinesis, cell motility, maintenance and modification of cell shape, and so on. They are associated with other intracellular proteins such as lamin, myosin, and spectrin within the biological system via extensive intracellular binding and cross-linking. One such association found is the contractile assembly, where microfilaments containing actin orient antiparallel with myosin filaments. These contractile rings are responsible for the cell division process.
As we know, the cell division terminates with the physical separation of the cytoplasm of a parental cell into nascent daughter cells, a process known as cytokinesis. And the contractile ring composed of F-actin and the motor protein (myosin II), along with structural and regulatory proteins, generates the constricting force to separate the cells during cytokinesis.
Cytokinesis begins during the late stage of karyokinesis (anaphase) in mitosis and meiosis. The actomyosin contractile ring is formed beneath the surface of the plasma membrane at the cell equator perpendicular to the axis of chromosome separation towards the end of telophase. When the contractile ring contracts, the plasma membrane linked to it constricts, and a cleavage furrow is created that separates the daughter cells apart between the separating chromosomes. Since plant cells lack myosin II, or contractile ring, their cytokinesis is assisted by the assembly of the microtubule-containing structure called the phragmoplast.

Note:
Cytokinesis in animal cells begins with cleavage plane specification or cleavage site selection process. Then the cleavage furrows initiate at a position midzone of the microtubule bundles. The position of radial arrays of microtubules (asters) depends on the prior position of the metaphase spindle. Subsequently, microtubules interact with the cell cortex to determine the cleavage furrow assembly site and assist in contractile ring assembly at the furrow region. Then, the spindle midzone containing microtubules promotes ingression of the cleavage furrow.