D2.1.2 Cytokinesis as splitting of cytoplasm in a parent cell between daughter cells Notes

Cytokinesis Splits the Cytoplasm Between Daughter Cells

1. It ensures that each daughter cell receives the necessary organelles, cytoplasmic components, and plasma membrane to function independently.
2. While nuclear division (mitosis or meiosis) separates the genetic material, cytokinesis completes the physical separation of the cell.

In Animal Cells, Cytokinesis forms The Cleavage Furrow

1. In animal cells, cytokinesis is driven by a contractile ring of actin and myosin proteins.
2. This ring forms just beneath the plasma membrane at the cell’s equator.

Steps of Cytokinesis in Animal Cells

1. Formation of the Contractile Ring
   1. Actin and myosin proteins assemble into a ring beneath the plasma membrane.
2. Cleavage Furrow Formation
   1. The contractile ring begins to tighten, pulling the plasma membrane inward.
   2. This creates a cleavage furrow, a visible indentation that deepens as the ring contracts.
3. Pinching the Cell Apart
   1. The contractile ring continues to constrict until the plasma membrane is pinched into two separate membranes.
   2. This process divides the cytoplasm and its contents equally between the two daughter cells.

In Plant Cells, Cytokinesis Builds a New Wall

1. Plant cells face a unique challenge during cytokinesis: their rigid cell wall.
2. Instead of pinching inward, plant cells construct a new cell wall and plasma membrane between the daughter cells.

Steps of Cytokinesis in Plant Cells

1. Formation of the Cell Plate:
   1. Vesicles from the Golgi apparatus, carrying cell wall materials (e.g., pectins and cellulose precursors), move to the cell’s equator.
   2. These vesicles align and fuse, forming a cell plate.
2. Expansion of the Cell Plate:
   1. The cell plate grows outward as more vesicles fuse, eventually connecting with the existing plasma membrane.
3. Formation of the Middle Lamella and Cell Wall:
   1. The fused vesicles form two layers of membrane, which become the plasma membranes of the daughter cells.
   2. Pectins are deposited between these membranes to create the middle lamella, which cements the two cells together.
   3. Each daughter cell then builds its own cell wall by depositing cellulose adjacent to the middle lamella.

Why Cytokinesis Matters

1. Cytokinesis ensures that each daughter cell receives a complete set of organelles and cytoplasmic components.
2. Without cytokinesis, nuclear division would result in a single cell with multiple nuclei, disrupting normal cell function.