Cytokinesis is a physical process of cell division, that normally takes place after mitosis. Cytokinesis is the physical division of the cell cytoplasm, the cell membrane, and cell organelles in eukaryotic cells to produce two distinct cells at the end of the cell cycle in both mitosis and meiosis.
In animal cells, cytokinesis is achieved when a contractile ring of the cell microtubules form a cleavage furrow that divides the cell membrane into half. The microtubules used during cytokinesis are those generated during the initial stages of division, and they contribute to the restructuring of the new cell. In the plant cell, a cell plate is formed that divides the cell into two.
Cytokinesis in animal cells
- The contractile ring is held together by the microtubules of the mitotic spindles.
- These microtubules and cell signals determine the location of the contractile ring and therefore they direct the plane of cell division, known as the division plane.
- The cleavage furrow forms around the division plane which eventually pinches off separating the cell into two cells.
- This is furtjer followed by a process of contraction and constriction by the contractile ring, made up of actin, myosin, and regulatory proteins.
- Actin and myosin are formed during interphase assembled in a cortical network o the filaments filled with actin and myosin.
- The contractile ring is positioned by the actin-myosin and regulatory proteins, and they also act as the motor proteins, allowing the contraction of the muscle cells.
- The muscle cells which are packed with actin filaments are pulled together by myosis
- After the exclusion of the cytoplasm and the organelles, the ring and the microtubules are left behind forming the midbody structure
- The cellular proteins cut and fusion of the plasma membrane are shut, while the extracellular elements that hold the cell together get dissolved, separating the cells.
- The separated cells may remain associated linked by the cytoplasm at bridges known as the gap junctions
Cytokinesis in plant cells
The major difference between an animal cell and a plant cell is that plants are made up of an extra-rigid cell wall, and therefore, a special kind of microtubules are involved in the completion of cytokinesis. These are known as the phragmoplasts.
- Phragmoplasts are vesicular spindle microtubules formed by Golgi vesicles during telophase on the metaphase plate
- When these Golgi vesicles fuse at the centre next to the cell wall, they form the cell plate, the site of plant cytokinesis.
- The more the vesicles fuse, the cell plate continues to enlarge, emerging at the periphery of the cell wall of the cell.
- The phragmoplasts carry vesicles of the cell wall to the newly formed cell plate
- Accumulated enzymes, structural proteins, and glucose molecules between the membranes by the Golgi apparatus during interphase contribute to the formation of the new cell wall
- The cellulose carried by the phragmoplast interact and combine forming the complex and strong rigid matrix of the plant cell wall.
- After the cell plate divides the cell, the plasma membrane seals off separating the two newly formed daughter cells.
- In between the two cells, trapped endoplasmic reticulum forms the plasmodesmata, space, or gap which allows the passage of molecules from one cell to another