Transcript The Cell Cycle

The Cell Cycle
Mitosis & Cytokinesis
Why do living things grow?
• This baby
king penguin
grows
because he
produces
more and
more cells.
How do cells know when to
quit dividing?
• Cell growth is CAREFULLY
controlled.
• Only certain cells are allowed to
divide rapidly.
–Ex. Hair follicles & stomach lining.
•One experiment using
cells in a petri dish
showed that they
stopped dividing when
they touched!
•But……
That’s not always the case…
Breast cancer cell
Liver Cancer cells
Mitosis
• The process where the
nucleus divides into two
new, IDENTICAL, nuclei.
During the early stages of
Mitosis…
• The chromatin (DNA +
Proteins) becomes
condensed (gets tighter)
and you can see the
chromosomes.
Chromosomes
• Chromosomes are tightly
coiled chromatin/DNA.
A Chromosome
*Two sister CHROMATIDS
Make up the chromosome
*The CENTROMERE, a sticky
Spot in the middle of the
Chromosome, keeps the sister
Chromatids together.
Interphase
• A long period between cell divisions.
• Doubling of all cell parts happens.
• Most cells, when looked at under the
microscope are in interphase
because it takes the longest time.
M
I
T
O
S
I
S
Mitosis is…
•The process of cell
growth & division
.
• There are 4 parts of Mitosis:
–P
–M
–A
–T
Prophase
Metaphase
Anaphase
Telophase
Prophase
Interphase
Anaphase
Telophase
Interphase
• This cell shows how all cells look
before mitosis.
• Interphase is a phase of the cell
cycle, but NOT a stage of mitosis.
Prophase
• The nuclear membrane breaks down.
• The chromosomes become visible
(shorten and thicken).
• The other structures important for
mitosis are also forming (ex. the
centrioles).
Metaphase
*The chromosomes are pulled to
the cell's equator by the spindle
fibers.
*The chromosomes MEET IN
THE MIDDLE
Anaphase
• The newly formed
chromosomes are pulled by
the spindle fibers, AWAY from
each other, toward opposite
poles of the cell.
Telophase
• The chromosomes stop moving.
• The spindle fibers break down.
• The membrane of the cell pinches
creating two separate cells.
• The nuclear membrane reforms.
• The nucleolus reappears.
Very Last Part…
Cytokinesis
• This is when the two new cells
completely divide.
• Plant and animal cells do this
differently!
Animal Cell
• A ring (contractile ring) tightens and
tightens until the two new cells pinch
apart.
Furrow
Plant Cell
• A cell plate forms between the two cells
and this forms into the cell wall eventually.