Study Guide for Cell Cycle
Cell Division Notes:
 There are 3 main reasons why cells need to divide:
1. To replace worn out cells
2. To replace damaged cells
3. Growth and Development
 Before a cell can divide, it must do two things:
1. Copy DNA
2. Copy Organelles
But why?
So that each new cell has a complete set of DNA and organelles
 Organisms with prokaryotic cells (_bacteria_) do a very simple process of dividing called
__binary _fission__. (draw below)
 However, eukaryotic organisms (_like us!_) go through a much more complicated
process called the _cell_cycle_, which is the dividing of non-sex cells. Sex cells divide
using a different process called _meiosis_.
 We can divide this process into _3_ main steps:
o _interphase_- cell grow and DNA is copied (90% of time spent here)
o _mitosis_- (4 steps) steps in which the nucleus’s DNA actually divides
o _cytokinesis_- cytoplasm splits and cell divides making two daughter cells
 In between each phase, there are _ checkpoints__ to make sure that the cell has done
everything it needs to do correctly.
 If a mistake has happened, the cell usually _fixes_ the mistake, but if it does not catch
the mistake, the cell could _malfunction_ (not work correctly).
 If cells do not divide correctly, _mutations_ or _cancer_ can occur.
Steps of the Cell Cycle
1st: Interphase
Chromosomes appear as threadlike
coils (chromatin) at the start, but then
coil up making chromosomes, then
are copied making sister chromatids.
2nd: Prophase
 Mitosis begins
 Centrioles appear and begin
to move to opposite ends
 Spindle fibers form between
poles
Nuclear membrane dissolves away
3rd: Metaphase
Chromatids (or pairs of chromosomes)
attach to the spindle fibers and line up
in the middle of the cell.
4th: Anaphase
 Chromatids (or pairs of
chromosomes) separate and
begin to move to opposite
ends of the cell.
5th: Telophase
 Two new nuclei form
 Chromosomes are starting to
uncoil back to chromatin
 Cell membrane starts to pinch
inward
 Mitosis Ends
6th: Cytokinesis
 Cell membrane completely
moves inward to create two
new daughter cells- each with
its own nucleus with identical
chromosomes.