Cytokinesis is a fundamental biological process where a single eukaryotic cell divides its cytoplasm into two distinct daughter cells. This division typically occurs after the nucleus has divided during mitosis or meiosis, marking the final stage of cell reproduction. The precise partitioning of cellular components ensures that each new cell receives the necessary materials for its survival and proper function. Cytokinesis is important for growth, tissue repair, and reproduction across various eukaryotic organisms.
Cytokinesis in Animal Cells
Cytokinesis in animal cells initiates with the formation of a cleavage furrow, which is an indentation on the cell’s surface. This furrow appears at the cell’s equator, positioned where the metaphase plate once was. The formation of this furrow is driven by a contractile ring located just inside the plasma membrane.
The contractile ring is primarily composed of actin filaments and myosin II motor proteins, similar to those found in muscle contraction. This actomyosin ring assembles equatorially and constricts, much like a drawstring tightening around a purse. As the ring contracts, it pulls the plasma membrane inward, deepening the cleavage furrow until the cell is pinched into two separate daughter cells.
Cytokinesis in Plant Cells
Plant cells, unlike animal cells, possess a rigid cell wall outside their plasma membrane, which prevents the formation of a cleavage furrow. Instead, cytokinesis in plant cells involves the construction of a new cell wall, called the cell plate, in the middle of the dividing cell. This process typically begins during telophase.
Vesicles originating from the Golgi apparatus, carrying materials for cell wall construction like cellulose and pectin, are transported to the cell’s equatorial plane. These vesicles are guided by a microtubule-based structure known as the phragmoplast. The vesicles then fuse together from the center outwards, forming a disc-shaped cell plate. As more vesicles fuse and their contents are deposited, the cell plate expands centrifugally until it merges with the existing parent cell walls, completely separating the two new daughter cells.
Key Differences in Cytokinesis
The fundamental distinction between cytokinesis in plant and animal cells lies in their mechanism of cytoplasmic division, dictated by the presence or absence of a rigid cell wall. Animal cells, lacking a cell wall, divide by an inward “pinching” action of a contractile ring. Plant cells, encased by a stiff cell wall, cannot constrict. Instead, they build a new cell boundary from the center outwards, forming a cell plate from Golgi-derived vesicles guided by the phragmoplast. Thus, animal cells constrict their membrane, while plant cells synthesize a new internal partition.