Mitosis

Cell Division is “Multiplication”

Each of us began life as a cell smaller than the period at the end of this sentence. All of the cells in our body have the same DNA, so each are essentially clones of each other.

How did we multiply from one to many cells? The answer is cell division. We learned in the previous lesson that cell division is a part of the cell cycle made up of mitosis and cytokinesis. Mitosis is the stage divides nuclei in an organized fashion so that you have two identical copies of DNA in each new cell.

Watch the following video reviewing mitosis. While doing so, think about this question: What is the result of mitosis?

Stop and Think: In the time it took you to watch this video clip, you lost 40,000 skin cells, yet you are not skinless. How does the information contained in the video clip explain why this is so?

Mitosis is a highly organized process that divides the nuclei of a cell into two nuclei. It aims to produce two daughter cells that have identical DNA. Keeping track of that DNA requires organization and cooperation in all parts of the cell.

There are four phases that we recognize in Mitosis. In reality, the cell does not pause as it moves through these stages; we have only given the events names to help us keep track.

Look at the stages of mitosis and cytokinesis below. Pay attention to the appearance and location of chromosomes (red structures).

MitosisFlow

Cytokinesis , or the separation of the cytoplasm, would occur after mitosis. Sometimes you will see cytokinesis begin to occur while telophase is completing.

Events in Mitosis and Cytokinesis

Take notes on the stages/events of Mitosis.

What is a spindle fiber? The spindle fibers are thin protein filaments that are constructed by the centrioles in prophase. Their role is pivotal in mitosis. They assist in guiding the chromosomes to separate properly. Spindle fibers attach to chromosomes at their centromeres. During mitosis, the centromere has a protein kinetochore attached that helps spindle fibers to control the chromosomes.

 

MitosisSpindle.png

Below is a summary graphic of the events of mitosis and cytokinesis. You can click on it to open a pdf to print and use as a study aid if you like. Add notes to it as necessary.

Mitosis_and_Cytokinesis (1)

Comparing Plant and Animal Cell Division

PlantAnimalMitosis.png

There are two important differences between cell division in animal cells and plant cells:

  1. In plant cells, cytokinesis occurs as a cell plate (which eventually forms a cell wall) begins to grow out from the center and merely separates the two daughter cells. In animal cells you would see a cleavage furrowduring cytokinesis instead.
  2. Plant cells do not have centrioles that form spindle fibers; there is a mysterious structure called the microtubule organizing center which performs the job of the centriole.

Examine the picture below of mitosis in plant cells, and try to find all the stages, including cytokinesis.

MitosisAllium.jpg