World Builders™                                                                Session Four  --  Microbiology

  Mitosis: 

          Asexual Reproduction for Eukaryotes    

Eukaryotes use a complex method of cell division to duplicate their chromosomes.


     As we have learned, when a prokaryote divides, it duplicates its loop of DNA and divides into two cells.  This works for prokaryotes, but eukaryotes are more complex, 

     Eukaryotes have their DNA in chromosomes in a nucleus in the cell.  Eukaryotes can also reproduce themselves by division, but they have a problem to solve.  How can the chromosomes be passed on so that each new cell gets a copy of every chromosome in the original cell?

     Eukaryotes use a process called mitosis for dividing one cell into two cells.  This is how it works. 

Mitosis: How the Cells Divide:

Asexual cell division is called Mitosis. Very, very, very simply, this is how it works.

Interphase: The cell appears to be resting  most of the time, but it is actually carrying on the ongoing functions of a cell, absorbing nutrients, utilizing oxygen, excreting wastes, making ATP, and keeping its system in balance.
Prophase:

The cell is getting ready to divide.

You can see chromosomes in the orange colored nucleus.

The gray structures that look like lines are the beginning of  structures called spindles.

Prometaphase:

The spindles go to opposite ends of the cell.
The spindles will pull the chromosomes apart.
Notice that the nucleus is no longer separate from the rest of the cell.

The chromosomes are starting to line up in the middle between the ends of the spindles. The chromosomes are floating freely.

 

Metaphase:

 

Now the chromosomes are lined up across the middle of the cell.

They divide so that there are now two copies of each one.

The spindles are about to pull copies of the chromosomes to each end of the cell.

Anaphase:

Now you can see the chromosomes being pulled toward the poles of the spindles.

You can see that this process duplicates and separates the chromosomes so that each new cell will be an exact copy of the old one.

 

Telophase:

This cell is ready to reconstruct a nucleus at each end of the cell.

The chromosomes are ready to be enclosed in a nucleus again.

The spindles are disappearing. Their job is done!

Cytokinesis

This cell is becoming two identical cells.
The nuclei have formed.
The chromosomes are loosening up.

At this last stage, the cytoplasm which fills the dividing cells is divided between them, and all the necessary extra parts are present in each new cell.

   Why is this process important to us? Well. it is still going on in our bodies. As our hair grows, the cells are dividing asexually. When our fingernails grow, there is asexual division again.

     When we cut our fingers and the skin heals, the cells go through this same process.

     When our bodies grow, this is how our bones get longer and tissues grow: the cells just divide!


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