Question

Describe the events that characterize each stage of mitosis.

Short answer

Question: Describe the main events that occur during each stage of mitosis. Answer: In prophase, chromatin condenses into chromosomes, nucleolus disappears, and spindle fibers start to extend from centrosomes. During prometaphase, nuclear envelope breaks down, and spindle fibers attach to the centromeres of chromosomes. In metaphase, chromosomes align along the metaphase plate with centromeres connected to spindle fibers. Anaphase involves the separation of sister chromatids, which are pulled towards opposite poles of the cell. Finally, in telophase, chromosomes decondense, nuclear envelope reappears, and spindle fibers dissolve, followed by cytokinesis, which results in two identical daughter cells.

Step-by-step solution

1. Prophase

During prophase, the first stage of mitosis, the chromatin inside the cell nucleus condenses and becomes visible as chromosomes. The nucleolus disappears, and the centrosomes, which are specialized organelles, move to opposite ends of the cell, forming the spindle apparatus. Microtubules start to extend from the centrosomes, preparing to attach to the chromosomes.

2. Prometaphase

In the prometaphase, the nuclear envelope breaks down, and the spindle fibers (microtubules) grow longer. The chromosomes become even more condensed and move towards the equator of the cell. Each chromosome consists of two sister chromatids joined by the centromere, which is the region where the spindle fibers attach.

4. Metaphase

The third stage, metaphase, is characterized by the alignment of the chromosomes along the cell's equatorial plane, which is also called the metaphase plate. The centromere of each chromosome is attached to spindle fibers originating from the centrosomes, ensuring that the sister chromatids will separate correctly in the next stage.

5. Anaphase

During anaphase, the sister chromatids are separated by the action of spindle fibers, which pull the chromatids apart at the centromere. Each chromatid is now considered a separate chromosome. The chromosomes are then pulled towards opposite poles of the cell by the shortening of the spindle fibers, making the cell elongate.

6. Telophase and cytokinesis

In the final stage of mitosis, telophase, the chromosomes arrive at the opposite poles of the cell and begin to decondense, forming chromatin again. The nuclear envelope reappears around each set of chromosomes, and the nucleolus reappears within the new nuclei. Spindle fibers dissolve, and the cell starts to return to a normal state. During cytokinesis, which occurs simultaneously with telophase, the cytoplasm and cell membrane are divided, forming two daughter cells with identical genetic material.