Cell Division

• Most cells reproduce through some sort of Cell Division
• Prokaryotic cells divide through a simple form of division called Binary Fission
• 3 step process

1. Single "naked" strand splits and forms a duplicate of itself.
2. The two copies move to opposite sides of the cell
3. Cell "pinches" into two new and identical cells (Cell wall then forms if applicable)

• Eukaryotes divide by a more complicated system called Mitosis
• This is because:

1. They have a nucleus which must be broken up and then reformed.
2. They have their DNA "packaged" in the form of Chromosomes
   • Chromosomes are composed of Chromatin
     • Made of DNA Strands
     • Also contain Histones - Proteins the DNA is wrapped around
3. They usually have more than 1 chromosome (humans have 23 pairs)
4. They have numerous organelles to distribute between the daughter cells.

• Most of the cell's life is spent doing its regular function.
• Cells divide along a rough time frame called its Cell Cycle.

• The Cell cycle consists of the folowing steps:

1. G1 (Gap 1) Phase - Cell performs its normal function (cells which do not divide stay in this stage for their entire life span)
2. S (Synthesis) Phase - Here the cell actively duplicates its DNA in preparation for division
3. G2 (Gap 2) Phase - Amount of cytoplasm (including organelles) increases in preparation for division.
4. Mitosis - Actual division occurs

• Mitosis is a 6 Stage process which is summarized in the table below:

	Name	Image	Description
1	Interphase		Cell Replicates its DNA/Chromosomes in preparation of upcoming division
2	Prophase		Chromosomes Shorten and become visible.Nuclear envelope disappears Centrioles begin to migrate to opposite poles of the cell Spindle & Astral Fibers   begin to form
3	Metaphase		Chromosomes line up along center of cell along the Metaphase Plate Chromosomes attach to spindle fibers Spindle and astral fibers now clearly visible.
4	Anaphase		Centromeres break up separating chromosome copies Chromosomes are pulled apart to opposite sides of cell Spindle & astral fibers begin to break down
5	Telophase		Nuclear envelope forms around both sets of chromosomes DNA uncoils Spindle & astral fibers completely disappear
6	Cytokenesis		Happens with most (but not all) cells. Cytoplasm & organelles move (mostly equally) to either side of the cell. Cell Membrane "pinches" to form 2 separate cells

Mitosis

Overview of Mitosis