Question

Describe the events that characterize each stage of mitosis.

Short answer

Question: Briefly describe the key events that happen in each stage of mitosis. Answer: In prophase, DNA condenses into chromosomes, nuclear membrane breaks down, and spindle fibers form. In metaphase, chromosomes align at the metaphase plate and spindle fibers attach to centromeres. In anaphase, sister chromatids separate and move to opposite poles of the cell. In telophase, chromosomes decondense, nuclear membranes reform, and spindle fibers disappear. Cytokinesis, though not a stage of mitosis, involves the division of cytoplasm, creating two distinct daughter cells.

Step-by-step solution

Prophase

During the prophase, the first stage of mitosis, the chromatin fibers of the DNA condense into chromosomes, which appear as sister chromatids joined together at a region called the centromere. The nucleolus disappears, the nuclear membrane begins to break down, and the mitotic spindle, made up of microtubules called spindle fibers, starts to form. The centrosomes, which are microtubule-organizing structures, begin to move towards opposite poles of the cell, forming the spindle apparatus.

Metaphase

In the metaphase, the chromosomes line up along the middle of the cell, also known as the metaphase plate or the equatorial plane. The spindle fibers coming from the centrosomes attach to the centromeres of the sister chromatids at the kinetochore, a protein structure. Each pair of sister chromatids is now held at the metaphase plate by the spindle fibers from both poles of the cell, ensuring equal distribution of the genetic material during cell division.

Anaphase

The third stage of mitosis, the anaphase, involves the separation of the sister chromatids to opposite poles of the cell. The centromeres split, and the spindle fibers begin to shorten, pulling the chromatids apart. The sister chromatids are now considered as individual chromosomes. The cell also elongates during this stage, preparing for cytokinesis, which is the division of the cell's cytoplasm.

Telophase

During the telophase, the final stage of mitosis, the chromosomes decondense, returning to their chromatin fiber state. The nuclear membrane reforms around each set of chromosomes, creating two distinct nuclei within the cell. The nucleoli also reappear in each nucleus. The spindle fibers disassemble and disappear, and the cell prepares for cytokinesis.

Cytokinesis (not a stage of mitosis, but an important part of cell division)

Cytokinesis typically occurs simultaneously with telophase. This process is the division of the cytoplasm into two distinct daughter cells, each containing a copy of the genetic material. In animal cells, cytokinesis involves the formation of a cleavage furrow that pinches the cell's membrane, eventually splitting the cell in half. In plant cells, a cell plate forms along the metaphase plate and gives rise to a new cell wall that separates the two daughter cells. By understanding the key events that take place in each of the stages of mitosis, you can grasp the overall process of how cells divide and transfer their genetic material to produce two identical daughter cells.