Notes 4-3
Cell Division
Cell Division
• How do you get bigger?
• Your cells grow and divide into 2 cells over and
over again.
• This is known as the cell cycle.
• The 2 new cells made are known as daughter
cells
The cell cycle
• The cell cycle is divided
into 3 stages:
1. Interphase
2. Mitosis
3. Cytokinesis
*Notice how long
interphase is, then
mitosis is short, and
cytokinesis is VERY
short!
Stage 1: Interphase
• Longest phase of the cell
cycle
• The cell is doing 3 major
things:
1. Growing
2. Copying its DNA
(process known as
replication)
3. Preparing for cell
division (preparing for
stage 2: mitosis)
• Why do you think the cell
must copy its DNA before
it divides?
After cell division, you end up
with 2 new cells. Each of these
cells must have its own copy of
DNA in order to carry out
functions.
Stage 2: Mitosis
• The cells nucleus
divides, each containing
a copy of DNA
• This way, each of the 2
daughter cells made
gets a copy of DNA
• Mitosis is divided into
four parts:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Let’s look at each phase!
Prophase
• Chromatin (DNA) in the
nucleus condenses into
X-like structures called
chromosomes
• Each part of the “X” of
the chomosome is an
identical copy of DNA
and is called a “sister
chromatid”
• The nuclear envelope
begins to disappear
• A spindle begins to form
Metaphase
• Chromosomes attach to the spindle fibers and
move to the middle of the cell
• Metaphase = middle!
Anaphase
• Each chromosomes are pulled apart
• Spindle fibers move each sister chromatid to
opposite sides of the cell
• Each chromatid is now called a chromosome
Telophase
• The cell begins to pinch off in the middle
• 2 Nuclear envelopes reform around each set
of chromosomes
• By now, the nucleus has successfully divided
into 2 distinct nuclei
Stage 3: Cytokinesis
• The cell membrane continues to pinch off
until the cell splits into 2 daughter cells
• Each daughter cell has an identical and
complete copy of DNA
• After cytokinesis, each daughter cell will then
immediately enter interphase, and restart the
cell cycle
• The process is endless
• This slide shows
you telophase
again at the top (1
cell but 2 nuclei),
and then
cytokinesis (2
cells, each with 1
nucleus)
• This is an animal
cell
Cytokinesis in plant cells
• Since plant cells have rigid cell walls, the
cytoplasm cannot pinch off like in animal cells
• Instead, a cell plate forms across the middle of
the cell
• The cell plate eventually turns into new cell
membranes between the 2 daughter cells, and
then the cell walls form around the new cell
membranes
Plant cell
The Cell Cycle
How to remember the steps…
• I-P-MAT, then cytokinesis
• This represents the order of all the parts of
the cell cycle… a teacher told me this silly
riddle once and I never forgot it!
• I-P-MAT (Don’t pee on your mat!!!) 