Mitosis - Cloudfront.net
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Cell Division
MITOSIS
When a living thing grows
are its cells getting bigger
or is the organism producing
more of them?
It is producing more cells. Cells of an adult are
usually no larger than cells of a younger
animal.
Why don’t our cells just
grow larger?
Cell Growth
There are many reasons cells just can’t grow to be
huge . . .
DNA overload – DNA controls the cell’s functions, but if
the cell were much larger the nucleus could not direct
all of that activity
Material Exchange – if our cells were larger it would
take materials a long time to reach their destinations
(cell membrane)
Cell Death – if we only had a few large cells and one
died it would be very detrimental to the entire organism
So, when cells reach a
critical size they . . .
Cell Cycles
Cells go through a
cycle that
determine when
they should grow
and when they
should divide.
There are four stage to the cell cycle:
G1 (Gap 1)
S Phase (DNA Synthesis)
G2 (Gap 2)
M-Phase (Mitotic phase)
Gap 1
The cell grows
They make new proteins and organelles
S-Phase
During this phase the DNA in the nucleus is
replicated
That means each leg of the chromosome is
copied
Gap 2
Organelles required for cell division are
created for example centroile
The centrioles are organelles that play a very
important role in mitosis
M-Phase
This is the phase the cell goes through to divide
Cell Division – the process cells go through to
split into two new daughter cells
There are two important parts to this:
Mitosis - the process eukaryotes go through to
replicate and divide their nucleus
Cytokinesis – the division of the cytoplasm during cell
division
DNA
One of the most important parts of cell
division is splitting up the DNA so that all cell
functions can be performed
There two different forms of DNA
Chromatin – DNA unwound with no particular
shaoe
Chromosomes – DNA that is tightly wound into an
X shape
Chromosomes
Sister
Chromatids
Centromere
Mitosis
There are four
stages to mitosis
Prophase
Metaphase
Anaphase
Telophase
Prophase
During prophase the chromatin starts to
condense (thicken and shorten) forming
chromosomes
The nuclear membrane begins to break down
The centrioles move to opposite end of the
cell
The centrioles start to create the spindle
fibers
Prophase
Metaphase
During metaphase the
chromosomes line up
along the middle of
the cell
The spindle fibers
lengthen and attach
to the centromere on
each chromosome
Metaphase
Anaphase
During anaphase the centromeres separate
splitting up the sister chromatids
The spindle fibers shorten pulling the sister
chromatids towards the centrioles at the
opposite ends of the cell.
Anaphase ends when the chromatids reach
the opposite ends of the cell and stop moving
Anaphase
Telophase
During telophase the nuclear envelop reforms
around the chromatids
As the this happens the chromatids relax
becoming chromatin again
The nucleolus also reappears
Telophase
Cytokinesis
This usually happens about the same time as
telophase
The cytoplasm separates and all of the
organelles separate into the new cells
Cytokinesis in Animal Cells
The cell membrane pinches inward until it
touches.
The cells
break off
and become
separate cells
Cytokinesis in Plant Cells
A cell plate forms
down the middle
of the cell
The cell
membranes
separates at the cell plate
The cell wall begins to form in the middle
of the cell plate
Mitosis Animation
http://www.teachersdomain.org/asset/lsps07
_int_celldivision/