Mitosis

Mitosis is a highly dynamic and controlled process in the cell cycle, during which DNA and components (organelles) of a cell are accurately divided into 2 identical daughter cells.

We can describe mitosis as consisting of 4 phases: prophase, metaphase, anaphase and telophase.

Quite a number of things happen during prophase.

  1. Chromatin (thread-like DNA) is supercoiled and condensed into chromosomes.

  2. The nuclear envelope breaks down, allowing the chromosomes to fill the entire cell space.

  3. The two centrosomes (or microtubule organizing centers, MTOCs) move apart to opposite ends of the cell.

  4. Microtubules from the centrosomes form mitotic spindles that can attach to the chromosomes to move them.
PROPHASE



The chromosomes are then moved by the mitotic spindle until they are all lined up in the middle of the cell, forming what is known as a metaphase plate. This stage of mitosis is called metaphase.

METAPHASE


Once all the chromosomes are "captured" by microtubules, the cell can proceed to anaphase. The mitotic spindles shorten, splitting the chromosome into two chromatids, and pulling each one to opposite ends of the cells.

If chromosomes are not segregated accurately, the resulting daughter cells will have errors and could become cancerous. To make sure that cells divide correctly, there are some internal checkpoints that stop the cell from continuing in the cell cycle if prior conditions are not met. For example, anaphase cannot take place until all chromosomes are attached to microtubules.

ANAPHASE


At the end of mitosis (telophase) we have two identical sets of DNA at the poles of the cell. This DNA starts to decondense back to the thread-like chromatin structure. A nuclear envelope reassembles around each set, forming 2 nuclei.

TELOPHASE


After mitosis has completed, the cell then divides into 2 daughter cells, a stage known as cytokinesis. Read more about this final stage of the cell cycle.

Animations make it really easy to understand the different phases of mitosis. Here's a really good one!



* All images here were modified from Molecular Biology of the Cell, 4th edition, Garland Science