Transcript MitosisPowerPoint 2011

The Cell Cycle
Mitosis and Interphase
Cells Make Cells…..Why?
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Grow
Repair
Regenerate or Replace
So wouldn’t it be easier to just be ONE cell?
Hhmm…let’s check out the surface
area to volume ratio….
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As the cell increases in size, could it move
substances in and out of the cell fast
enough?
Therefore, cells are…
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SMALL!!
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HAVE UNIQUE
SHAPES TO
INCREASE
SURFACE AREA
Prokaryotic Cell Division
 Bacterial
cells reproduce by
Binary Fission
 Much
simpler process than in
eukaryotic organisms (why?)
Prokaryotic Cell Division
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Begins with DNA replication
(why?); each copy moves to
opposite sides of cell
Followed by elongation of cell,
and formation of a septum
(separation) between the two
halves, forming two new cells
Prokaryotic Cell Division

Results in two cells that are
identical (clones) of original cells
Eukaryotic Cell Division
Two forms
 Mitosis
grow, replace dead or worn
out cells, or to repair wounds
Asexual reproduction in
fungi, protists, some
plants/animals
 Meiosis
Sexual reproduction
DNA and Cell Division
 During
cell division, the
genetic material DNA, needs
to be copied and divided
between the two new cells
 DNA
in cells is divided into
long chains called
chromosomes
All living things..
..begin life as a
single fertilized
cell.
Humans begin as a
fertilized OVUM
or human egg
cell.
The egg cell …
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….then begins to
divide into exact
duplicate “stem
cells”.
these first cells will
be the basis for all
future cells in the
human body.
---->note the ovum
has divided into 8
stem cells
How does this work?
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Let’s go back
to the little
batch of 8…
We will now
look at cells
when they are
dividing…and
when they
aren’t!
This little batch of cells…
 …will not stay
the same.
Cells
specialize and
take on
different jobs.
Interphase
The time
between cell
division
 Cell is doing its
job
 DNA duplicateschromosomes
make exact
copies of
themselves
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Genetic material is
all strung out as
chromatin
Nuclear
membrane
clearly in
place
The Cell Cycle
G0
The Cell Cycle: Interphase
When a cell is not dividing it is
said to be in Interphase:
 G1: Gap, cells are recovering
from an earlier cell division
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S: Synthesis, DNA
replication occurs
The Cell Cycle: Interphase G2
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Gap, cells are making sure all the
DNA was replicated correctly; a
little more growth; the
chromosomes start to become
tightly coiled; Centrioles
replicate and one centriole
moves to each pole. *Animal
Cells*
REVIEW:
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In a non-dividing cell, the DNA is called
CHROMATIN.
 During the S phase of the cell cycle,
the DNA replicates to form sister
CHROMATIDS.
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In a dividing cell, the DNA is called
CHROMOSOMES.
Cell cycle
 Two
main parts:
 Interphase
 Cell
division
Eukaryotic Chromosome
Structure
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Normally,
chromosomes are
spread out in a
form called
chromatin
During mitosis,
chromosomes
fold up and
condense
Chromosome structure
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The replicated chromosomes stay
together and are called sister
chromatids
Sister chromatids are attached at the
centromere
The Cell Cycle: Cell Division
 Mitosis
(M Phase)
 Nuclear Division
 Cytokinesis
(C phase)
 Cytoplasmic Division
The Cell Cycle
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The length of time the cell cycle takes
depends on the type of cell. Usually
the more specialized the cell the less
likely it is to divide.
Red blood cells are replaced at a rate
of 2-3 million/sec
Nerve cells usually never divide, they
enter G0
Mitosis
 Cell
divides to form two new cells
 Can look at four different stages
 Prophase
 Metaphase
 Anaphase
 Telophase
Prophase
 DNA
condenses
to form distinct
chromosomes
 Nuclear
membrane
disappears
Metaphase
Chromosomes
line up in the
middle (equator)
of the cell
 Spindle fibers
attach
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Anaphase
 Chromosomes
separate and
move toward
the opposite
ends of the cell
(poles)
Telophase
 Chromosomes
reach the poles
 New nuclear
membrane forms
 Chromosomes
unwind to become
thread-like
chromatin again
Cytokinesis (End of Telophase)
The cytoplasm is
evenly divided
 New cell
membrane forms
in animal cells
 New cell wall is
built across for
plant cells
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OK, fine…but who really
cares about MITOSIS and
dividing cells???
Nerve cells…
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…remain
in
INTERPHASE for
long periods of
time.
They go through
mitosis about once
every 75 years.
So?…
Damage to these cells…
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…is often very
serious.
Some damage is not permanent
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Gloria Estefan was
involved in a tragic tour
bus accident.
Surgeons were able to
repair her nearly severed
spinal chord.
She recently donated
$1,000,000 for spinal
cord injury research--->
Cancer cells…
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…behave
much differently
than nerve cells.
…spend very little time in
interphase and go through
mitosis uncontrollably.
Approx. 1/10,000 of your
cells are cancerous-the good
news-your defense cells
usually kill them fast.