What happens in the four stages of mitosis?

Wednesday, January 20, 2021

In 1855, Rudolph Virchow, a German scientist, discovered that all cells come from other cells. How do cells produce more cells? Cells go through a carefully regulated process called the cell cycle that consists of two main phases: interphase and mitosis. At the end of the cell cycle, the original cell splits, resulting in two daughter cells. Today, we will focus on mitosis. We will learn about the four steps of mitosis and what occurs during each.  Mitosis occurs after interphase.


Interphase is the first phase of the cell cycle in which cells grow, replicate their DNA, and make sure they are healthy and ready to divide. It is the longest phase in the cell cycle.

Once interphase is completed, the first step of mitosis begins. This first step is called prophase. During prophase, four main events occur: 

1) Chromatin (genetic material containing DNA, RNA, and proteins) condenses into threadlike structures called chromosomes. These chromosomes are x-shaped, and have left and right “arms” (sister chromatids) that are joined in the center by centromeres. 

2) Centrosomes are organelles that act as the cell’s organizer during mitosis. During prophase, centrosomes separate and move toward opposite ends of the cell. 

3) The centrosomes begin to produce threads called spindle fibers. These spindle fibers will attach to the chromosomes and move them around during the other steps of mitosis. 

4) The membrane (or envelope) around the cell’s nucleus dissolves. This is what gives the centrosomes’ spindle fibers the ability to attach to the chromosomes. 


The second step in mitosis is called metaphase. During metaphase, the centrosomes’ spindle fibers pull the chromosomes toward the middle of the cell, arranging them in a neat line. The cell will go through the “spindle checkpoint” to make sure the chromosomes are lined up properly and correctly attached to their spindle fibers. This ensures that the sister chromatids will split evenly during the next step of mitosis. More importantly, this step helps guarantee that after cell division, the two daughter cells will contain identical genetic material.  


The third step in mitosis is called anaphase. During anaphase, the spindle fibers pull the sister chromatids apart, moving them to opposite ends of the cell from one another. In addition, the cell is elongating in preparation for cell division. Anaphase is the shortest step in mitosis. 


The last step of mitosis is called telophase. During telophase, the separated chromosomes on either side of the cell gain nuclear membranes, causing the cell to temporarily have two nuclei. Telophase lasts for about an hour, during which the cell is continuing to elongate. Then, the cell is ready to separate. The fluid inside the cell, or cytoplasm, splits in half, resulting in two daughter cells. This cytoplasmic division is called cytokinesis, and it marks the end of mitosis. 


In summary, cells multiply by making copies of themselves during the cell cycle. There are two main phases of the cell cycle: interphase and mitosis.

Cells grow and make copies of their DNA during interphase. After double checking to make sure it completed interphase properly, the cell moves into mitosis.

Mitosis consists of four main steps: prophase, metaphase, anaphase, and telophase. At the end of mitosis, division of the cytoplasm, or cytokinesis, occurs. You now have two cells with identical genetic material. 

Here are some tricks to help you remember this information: 

*The latin prefix “pro” means “before”. Prophase occurs before all the other steps in mitosis.

*During metaphase, the chromosomes align in the center of the cell. Think “m” in metaphase for “middle” of the cell. 

*During anaphase, the sister chromatids are pulled away from each other. Think ‘a’ in anaphase for “away”. 

*During telophase, the recently separated sister chromosomes are on opposite ends of the cell from one another, and they live inside different houses (nuclei). The chromosomes now need a “telo”phone to communicate with each other. 

*You can use the acronym “PMAT” to help you remember which order the steps occur in.

Relevant links:

All about Genetics

What is a trait?


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