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CELL DIVISION
Cell Division/Reproduction
Why?

Cells divide for many
reasons:
 In order to stay small
 Diffusion occurs at a
faster, more efficient
rate in smaller cells.
 Why would diffusion
rate matter in cells?
 Remember what
materials need to
enter and exit the
cell.
DNA limits their size
 DNA can only control
cells up to a certain
size.
 Repair/replace old or
damaged cells.
 Growth and
Development
 We start out as one
cell, mitosis allows that
1 cell to turn into
billions of cells.

Cell Cycles
Prokaryotic Cells
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No nucleus
No membrane bound
organelles (ex. mitochondria,
vacuole, chloroplast)
 A.) Cell division takes
place in 2 steps:
 1.) DNA is copied
 2.) Cell splits by binary
fission
Cell Cycles
Eukaryotic Cells
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Contain a nucleus and
organelles.
 Repeating sequence of
growth and division
Occurs in two cycles for two
purposes
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Mitosis
 Occurs in somatic (ordinary
body cells) for growth and
repair
 Creates 2 identical cells
Meiosis
 Occurs in germ cells
(ovaries and testes) to
make gametes (sex cells).
 Creates 4 similar cells.
Eukaryotic Cell Cycle

3 Stages
 Interphase
 G1: First growth phase
 S: Synthesis phase
 G2: Second growth phase
 Mitosis
 nuclear division
 Prophase
 Metaphase
 Anaphase
 Telophase
 Cytokinesis
 Division of cytoplasm
Centromere
Interphase

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G1 – first growth phase:
 The cell doubles in size
and the organelles double
S – synthesis phase:
 the DNA that makes up
the chromatin is copied
(DNA replication) this is
the longest phase of
interphase.
G2 – second growth phase:
 Growth and preparation
for mitosis, second checkpoint.
This is when the cell is
preparing to divide.
 The LONGEST phase of the
cell cycle
 90% of the cell’s life is
spent in Interphase.

Interphase (G1, S, G2)
Terms to know: (Start a VOCAB page)
DNA related terms
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Chromosome
 Single piece of coiled DNA
Diploid
 A cell that contains a set of
chromosomes from mom and
dad. (46 in Humans)
Replicated Chromosome
 A single piece of DNA that
has been copied through DNA
replication
Sister Chromatids
 2 identical strands of DNA
Non-Replicated Chromosome
 Single strand of DNA before
it is copied
Structural Terms

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Spindle Fibers
 Fibers that are attached to
centrioles to help pull
apart chromosomes
Centrioles
 Organelles that aid in
pulling apart chromosomes
Centromere
 Structure that holds the
replicated chromosomes
together
Mitosis (PMAT)

Mitosis
 The nucleus of a cell is
divided into two nuclei
with the same number
of chromosomes.
 Cell Stays diploid
 Consists of 4 phases
 Prophase
 Metaphase
 Anaphase
 Telophase
Mitosis Step1: Prophase

Longest phase of MITOSIS
 Chromatin
coils and
forms chromosomes
 Nuclear envelope
breaks down
 Spindle fibers form
and stretch from one
end of the cell to the
other
 They
attach to the
centrioles
 They help to pull the
cell apart
Mitosis Step2: Metaphase

Chromosomes line up
in the middle of the
cell
Mitosis Step3: Anaphase
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Centromere of each
chromosome splits
Two sister chromatids
separate and move to
opposite poles
Each chromatid
becomes separate
(non-replicated)
chromosome in each
daughter cell.
Mitosis Step4: Telophase

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Last stage of Mitosis
Chromosomes at each
pole uncoil and
become chromatin
Nuclear envelope
reforms
Spindle fibers break
down
Cytokinesis
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NOT part of mitosis
The cytoplasm divides
into two cells
Cell membrane
reforms
In plant cells the cell
wall reforms