Cytokinesis is the final step in cell division, where a parent cell divides its cytoplasm and contents to form two distinct daughter cells. This follows nuclear division (mitosis or meiosis), ensuring each new cell receives a complete set of genetic material. Cytokinesis partitions the cell’s internal components, allowing independent functioning. Without this division, cells would become multinucleated, disrupting normal biological processes.
How Cytokinesis Occurs in Animal Cells
Cytokinesis in animal cells begins during the late stages of nuclear division, in anaphase or early telophase. A specialized contractile ring forms inside the plasma membrane at the cell’s equator. This ring is composed of two protein filaments: actin and myosin II. These proteins, also responsible for muscle contraction, allow the ring to generate force.
Actin filaments organize into a ring that interacts with myosin II, a motor protein. As myosin II moves along the actin filaments, the contractile ring tightens, like pulling a drawstring. This action pulls the cell membrane inward, creating a cleavage furrow.
The furrow deepens, constricting the parent cell into two. This continues until the cell is completely pinched apart, resulting in two daughter cells, each enclosed by its own plasma membrane. The contractile ring’s positioning is guided by central spindle microtubules, ensuring accurate division.
How Cytokinesis Occurs in Plant Cells
Plant cells use a distinct mechanism for cytokinesis due to their rigid cell wall, which prevents cleavage furrow formation. Instead, a new cell wall is constructed between the two daughter nuclei. This process begins with the formation of the phragmoplast, which develops from remnants of the mitotic spindle. The phragmoplast is a complex network of microtubules and actin filaments that forms in the center of the dividing cell.
Within the phragmoplast, vesicles from the Golgi apparatus accumulate and fuse at the cell’s equatorial plane. These vesicles carry components for building a new cell wall and plasma membrane. As more vesicles fuse, they form a flattened, disc-like structure known as the cell plate. The cell plate expands outwards from the center towards the existing parental cell walls. Once the cell plate reaches and fuses with the original plasma membrane and cell wall, it establishes a complete new cell wall, dividing the parent cell into two daughter cells.
Why Cytokinesis is Essential
The successful completion of cytokinesis is essential for organism functioning and survival. Following nuclear division, cytokinesis ensures each newly formed daughter cell receives an equitable distribution of cytoplasmic contents, including organelles. This balanced partitioning is necessary for the viability and functionality of the daughter cells.
If cytokinesis fails after nuclear division, the result is a single cell with multiple nuclei. Such multinucleated cells can lead to abnormal development and various cellular dysfunctions. Cytokinesis also supports processes like growth by increasing cell number. It plays a role in tissue repair by generating new cells to replace damaged or old ones, and is part of reproduction, particularly asexual reproduction, by creating genetically similar and functional offspring cells.