D2.1.7 Phases of mitosis Notes

There Are 4 Phases of Mitosis

1. Mitosis is divided into four distinct phases: prophase, metaphase, anaphase, and telophase.
2. Each phase plays a critical role in ensuring the accurate distribution of chromosomes.

Prophase Prepares Cells for Division

Prophase is the first phase of mitosis, where chromosomes condense, the nuclear envelope breaks down, and the mitotic spindle begins to form.

1. During prophase, the chromatin (loosely packed DNA) condenses into visible chromosomes.
2. Each chromosome consists of two sister chromatids joined at a centromere.
3. The nuclear envelope begins to break down, allowing the chromosomes to move freely in the cytoplasm.
4. Microtubules assemble into a mitotic spindle, which will guide the chromosomes during division.

Metaphase Aligns the Chromosomes

Metaphase is the second phase of mitosis, where chromosomes align at the cell’s equator, attached to spindle fibers.

1. Chromosomes line up along the metaphase plate (the cell’s equator).
2. Spindle fibers attach to the kinetochores (protein structures) on the centromeres of each chromatid.
3. This alignment ensures that each daughter cell will receive one copy of each chromosome.

Anaphase Separates the Sister Chromatids

Anaphase is the third phase of mitosis, where sister chromatids are pulled apart to opposite poles of the cell.

1. The cohesin proteins holding the sister chromatids together are broken down.
2. Spindle fibers shorten, pulling the sister chromatids apart toward opposite poles of the cell.
3. Once separated, each chromatid is considered an individual chromosome.

Telophase Reforms and Relaxes the Cell

Telophase is the final phase of mitosis, where nuclear envelopes reform around the separated chromosomes, which decondense back into chromatin.

1. Nuclear envelopes reform around the two sets of chromosomes at each pole.
2. The chromosomes decondense back into chromatin, becoming less visible under a microscope.
3. The spindle fibers disassemble, and the cell prepares for cytokinesis (the division of the cytoplasm).

Cytokinesis Completes Cell Division

Cytokinesis is the process of dividing the cytoplasm to form two separate daughter cells.

1. In animal cells, a cleavage furrow forms, pinching the cell into two.
2. In plant cells, a cell plate forms, eventually developing into a new cell wall.