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Cell Division
Ch. 10
Why do cells divide?
(1)
Exchanging materials
The larger a cell becomes, the
harder it is to get enough materials
and waste across the cell
membrane.
Why do cells divide?
(2)
DNA Overload
Larger cells place more demands on
their DNA.
Why do cells divide?
(3)
Surface Area : Volume Ratio
As the length of a cell increases, the
volume increases much more rapidly
than surface area.
The Cell Cycle
Interphase (period in-between division)
– G1 (growth)
– S (DNA replication)
– G2 (prepare for mitosis)
M phase (division)
– Mitosis (division of the nucleus)
– Cytokinesis (division of the cytoplasm)
Most of the time the cell is in interphase!!!
Mitosis
Mitosis is the division of the nucleus.
There are 4 stages of mitosis:
– Prophase
– Metaphase
– Anaphase
– Telephase
Prophase
Everything sets up for mitosis.
First and longest stage of mitosis.
The chromatin condenses into chromosomes.
The centrioles separate and form a spindle of
microtubules.
The nuclear membrane breaks down.
Metaphase
Metaphase is the 2nd phase of
mitosis.
Chromosomes line up on the spindle
in the MIDDLE of the cell.
May last only a few minutes.
Anaphase
Anaphase is the 3rd phase of mitosis.
Chromosomes are pulled APART to
opposite ends of the cell.
Begins as soon as the chromosomes
begin separating and ends as soon
as the chromosomes stop moving.
Telophase
Last phase of mitosis.
Chromosomes disperse and tangle.
The nuclear envelope forms around the
chromosomes.
The spindle breaks down.
The nucleolus becomes visible.
Cytokinesis
The division of the cytoplasm.
Occurs at the same time as telephase.
The cytoplasm can be divided 2 ways:
– Animal cells pinch off into 2 cells.
– Plant cells form a cell plate (which is the
beginning of the cell wall)
Final Product
The final product of mitosis
and cytokinesis is:
–2 genetically identical daughter
cells
Controls of Cell Growth
When cells come into contact with
other cells, they stop growing.
Cyclins are proteins that regulate the
timing of the cell cycle.
Cancer
Cancer is a disorder where the cell has
uncontrolled growth.
Cancer cells do NOT respond to
regulators.
This causes the cells to form masses
called tumors, which can damage
surrounding tissues.