Tuesday, September 28, 2010

The Cell that Divides

Have you ever wondered how your cuts and bruises heal, how sperm and eggs are formed, or how cancerous cells go out of control????

CELL DIVISION!!!

There are 2 types of cell division: mitosis and meiosis.  They are each a part of a larger process called the cell cycle.

The cell cycle has 3 stages or steps:

1. Interphase - during this step the cell is growing, organelles are replicating, and the DNA is copying its code.  It takes the majority of cell cycle's time.

2. Mitosis or Meiosis - during this stage the cell's nuclear material (DNA) is divided equally among resulting cells.

3. Cytokinesis - during this quick stage, the cell's cytoplasm divides and the cell membrane pinches or cleaves to finally form 2 separate cells.

http://staff.jccc.net/pdecell/celldivision/images/cellcycle.gif



 MITOSIS!
Now lets get more detailed information about mitosis.  There are 4 stages of mitosis: prophase, metaphase, anaphase, and telophase.

Once a cell has entered mitosis, it already has a duplicate copy of each strand of DNA that was created during interphase.

1. Prophase
a. chromosomes become visible as sister chromosomes that look like a series of Xs
b. nuclear envelope disintegrates
c. nucleolus also disintegrates
d. centrioles begin to migrate towards opposite poles and to form spindle fibers.

http://www.biologycorner.com/resources/mitosis/prophase.gif
http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/mitosis/pcprophaseB.html
 2. Metaphase
a. each pair of sister chromatids (1 chromosome at this point) lines up in a straight line down the equator (i.e. center of the cell) much like we line up in a line for a movie or to get a meal at a fast food joint.

b. Centrioles that are now at opposing poles attach their spindle fibers to each centromere to prepare to pull each sister chromatid to their respective poles.

http://t2.gstatic.com/images?q=tbn:czhejdprkVlnhM:http://utpa.net/Epithelium/projections/metaphase.JPG&t=1
http://www.uic.edu/classes/bios/bios100/lecturesf04am/metaphase.jpg
3. Anaphase
a. centrioles pull each sister chromatid away from its partner and toward opposing poles

http://www.microscopy-uk.org.uk/mag/imgnov04macro/anaphase.jpg
http://www.ias.unt.edu/~tpp001/anaphase_text.JPG
http://mail.watertown.k12.ma.us:81/~kboudreau/study%20guides/wmssg/gr7hp/gr7sci/sg/Gr7SGrfx/anaphase.jpg
4. Telophase
a.Cell boundaries start to reform
b.2 new nuclei from around their new DNA package in separate areas.
c. Cell begins to look pinched as it prepares for cytokinesis

http://www.karlloren.com/biopsy/images/telophase.jpg
http://www.microbiologyprocedure.com/genetics/cell-divisions/images/telophase.jpg
After mitosis, the cell splits its cytoplasm, closes up its cell membrane, and presto we have 2 cells.

Below is a summary of the cell cycle using a special kind of microscope that relies on fluorescence

http://www.biology.ed.ac.uk/research/groups/earnshaw/mitosisGrL.gif


http://micro.magnet.fsu.edu/cells/fluorescencemitosis/images/mitosisintrofigure1.jpg

Finally, as a total review of mitosis click on the link below to watch a WONDERFUL mitosis video.

Mitosis YouTube Review Video



Tomorrow we will review meiosis which is the process by which an organism forms gametes or sex cells each having half the set of chromosomes as the original cell.

Until then....may your cells divide with a quickness that heals all your worries and woes and makes you appreciate each day we are given to study biology!

Love ya! Mean it!

1 comment:

  1. Nice writeup..keep writing :-) very useful it is.. Thank you..

    ReplyDelete