Make your own free website on Tripod.com








Cell Reproduction

6-2 Mitosis and Cell Division














Home | 6-1 Chromosomes | 6-2 Mitosis and Cell Division | The Cell Cycle | 6-3 How Gametes Form: Meiosis | Vocabulary





When cells get so big they either stop growing or they divide into two cells. In order for a cell to divide and make two working cells it has to first copy the genetic information.

Bacteria Simply Split.

Cell division in bacteria is a lot more simple then when eukaryotic cells divide. First the bacterium gets bigger. Then its single cirlce of DNA attaches to the inner surface of the cell membrane and makes a copy. The copy attaches to a differnt part of the inner wall. After it makes a copy, new membrane and wall materials start to form in the middle of the cell, away from the the two chromosomes. The the cell pinches itself together to make two instead of one. It takes about 20 minutes for bacteria to divide.
 

bio8.jpg
Bacteria just after division.
















Mitosis

Eukaryotic cell division is a lot differnt from bacterial cell sivision. First each chromosome must be copied exactly. Then the chromosomes must be sorted out so that each new cell gets a complete set. Finally the cell can divide in half.
 
There are two processes that have evolved that make it possible for eukaryotic cells to divide sucessfully.Those two processes are mitosis and cell division. Mitosis is the process when the bucleus of a eukaryotic cell divides to form two nuclei, each containing  a complete set of the cell's chromosomes.
 
The first stage is Interpahse. Cromosomes are nto yet visible. The DNA of each bhromosome consits of two identical strands.
 
The second stage is Propahse. This is when mitosis begins. The chromosomes coil into short fat rods. The nuclear envelope breaks up and a network of protein cables called spindle fibers assemble across the cell.
 
The thrid stage is Metaphase. Chromosomes attach to the spindle fibers and line up in the middle of the cell.
 
The fourth stage is Anaphase. Each chromatid seperates from its identical copy. Chromosomes are pulled to the opposite sides of the cell. The spindle fibers begin to break down.
 
The fifth stage is Telephase. The nuclear envelope forms around each set of chromosomes. The chromosomes uncoil so that the proteins can be bullt. The spindle fibers disappear.
 
The first five stages are easy to remember. All you have to do is remember 'IPMAT'.
 
The last stage is Cytokinesis. This is when the cytoplasm is pinched in half, forming to new, identical cells.
 
















bio9.gif

"Biology is the only science in which multiplication means the same thing as division."