The Cell Cycle

What is the cell cycle?

• The cell cycle is the growth and division of a cell into two daughter cells...from there, 2 cells become 4 cells, 4 cells become 8 cells, and so on...get it?

The cell cycle is made up of three major parts:

1. Interphase-the part of the cell cycle between cell divisions (mitosis and cytokinesis).
2. Mitosis (mitotic phase)-the division of the chromosomes and nucleus into two separate, but equal nuclei (one for each cell).
3. Cytokinesis-distribution of the cytoplasm into two separate cells, happens just after mitosis.

Now, Interphase is made up of three smaller phases as well:

1. G1- is the first gap or growth phase. During G1 phase, the cell does most of its growing and performs its daily functions.
2. S-is the synthesis phase. During S phase the chromosomes duplicate.
3. G2-is the second gap phase. During G2 phase, the cell preps for cell division (mitosis and cytokinesis.

*Note: there is also a G0 phase, which is outside of the cell cycle...this phase is for non-dividing cells (i.e. nerve cells).

Mitosis is also made up of smaller phases:

1. Prophase-during prophase, the chromosomes condense and the nuclear membrane disintegrates.
2. Metaphase-during metaphase, the paired chromosomes line up exactly in the middle of the mitotic spindle.
3. Anaphase-during anaphase, the chromosomes split at their centromeres, and one half move to each pole of the dividing cell.
4. Telophase-during telophase, the chromosomes have stopped moving, and a new nucleus forms in each cell. The mitotic spindle breaks up, and cytokinesis is ready to begin. So, teleophase is pretty much the opposite of prophase.

So the whole process is:

• Interphase-G1 --> S --> G2 to....
• Mitosis- Prophase---> Metaphase--->Anaphase--->Telophase to....
• Cytokinesis: splitting of the cytoplasm.
• Done. We now have two cells from one.
• REPEAT!

Okay, so that is definitely a lot of information and moving around of cellular stuff to try to just imagine in your head. Here's some links to help clarify the whole thing.

These two are good animations of the cell cycle:

• http://www.csuchico.edu/~jbell/Bio1207/animations/mitosis.html
• http://www.cellsalive.com/mitosis.htm

This one is kind of neat, kind of cheesy. It's a cell cycle game. Hey, at least your not stuck reading your book, right?

• http://nobelprize.org/medicine/educational/2001/