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MITOSIS
To be answered ----THINK
 How many cells are you composed of?
 When an organism grows bigger, do you get more
cells or just bigger cells or both?
 When do your cells divide the fastest? Slowest?
 Do all cells continuously divide? Why or Why n’t?
 Are all cells capable of division and replacement?
 Why would a cell divide?
 When would a cell divide?
ANSWERS
 How many cells are you composed of?- Many cells
 When an organism grows bigger, do you get more cells or
just bigger cells or both? – More cells and bigger cells also
 When do your cells divide the fastest? Slowest? - Fastest
and slowest
 Do all cells continuously divide? Why or Why n’t? –
YES1. Some cells do continuously divide, such as epithelial (skin)
cells, cells in the gastrointestinal tract and blood cells in
the bone marrow.
2. The cells that keep on dividing, even though they are not
supposed to, are cancer cells. They eat up all your nutrients
and form tumors etc.
NO- There are some cells that are extremely specialized such as
neurons, heart cells, and skeletal muscle cells, which will not
divide.
 Are all cells capable of division and replacement?
NO
Permanent cells are cells that are incapable of
reproduction as adults. This includes brain cells,
heart cells, and skeletal muscle cells.
Stable cells are cells that multiply only when needed.
They spend most of the time in the quiescent G0
phase of the cell cycle, but can be stimulated to
enter the cell cycle when needed. Examples include:
the liver, the proximal tubules of the kidney, and
endocrine glands.
labile cells are cells that multiply constantly
throughout life. They spend little or no time in the
quiescent G0 phase of the cell cycle, but regularly
perform cell division.
Why does a cell divide? - As cells absorb nutrients
and get larger, the volume of the cell increases faster
than the surface area.
• This means that a cell can no longer absorb nutrients
and get rid of wastes fast enough to support its
demands (volume)
• So what’s a cell to do?
– Solution: divide in 2!
Surface area
for exchange
not great
enough to
support cell’s
needs
When would a cell divide?
• Growth
• Repair or Replacement
• Cancer
Different cells divide at different rates:
Most mammalian cells = 12-24 hours
Some bacterial cells = 20-30 minutes
Yeast cell – 2 hours
Amoeba – a few days
Human embryo cell – 15-20 minutes
Human adult cell – 8 hours to 100 days
How does cell division change over a lifetime?
All cells die after a certain number of
divisions (programmed cell death). At any
given time some cells are dividing and
some cells are dying.
Example:
• Childhood = cell division > cell death
• Adulthood = cell division = cell death
• The Later Years (Aging) = cell division < cell
death
MITOSIS
• Mitosis is the process in which the
nucleus divides to form two new
nuclei.
(OR)
• Equal distribution of the 2 sets of DNA
amongst the 2 daughter cells.
• Mitosis: Division of somatic (body) cells
• Mitosis: Asexual Reproduction
MITOTIC PHASES
4 Stages:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Interphase
occurs before mitosis begins
• Chromosomes are copied (# doubles)
• Chromosomes appear as threadlike coils
(chromatin) at the start, but each chromosome
and its copy(sister chromosome) change to sister
chromatids at end of this phase
Nucleus
CELL MEMBRANE
Cytoplasm
As cell enters mitosis
from interphase it has
2 complete sets of
chromosomes because
of replication in the S
phase. Each set must
be re-arranged and
distributed into the 2
new daughter nuclei.
This is mitosis.
Prophase
Chromosome pair up!
1. Chromosomes thicken and shorten
-become visible
-2 chromatids joined by a centromere
2. Centrioles move to the opposite sides of the nucleus
3. Spindle fibers form between the poles.
4. Nucleolus disappears
5. Nuclear membrane disintegrate
Sister chromatids
Centrioles
Spindle fibers
Prophase
Animal Cell
Plant Cell
Spindle fibers
Centrioles
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
METAPHASE
• Chromosomes meet in the middle!
1. Chromosomes arrange at equator of
cell
2. Become attached to spindle fibres by
centromeres
Metaphase
Animal Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Plant Cell
Anaphase
• Chromosomes get pulled apart
1. Spindle fibres contract pulling
chromatids to the opposite poles of
the cell
Anaphase
Animal Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Plant Cell
Telophase
•
1.
2.
3.
4.
5.
Now there are two!
Chromosomes uncoil
Spindle fibres disintegrate
Centrioles replicate
Nucleur membrane forms
Cell divides
Telophase
Animal Cell
Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm
Plant Cell
Animal Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
Plant Mitosis -- Review
Interphase
Prophase
Metaphase
Anaphase
Telophase
Interphase
The Guarantee of Mitosis…
Why is this so important?
The 2 daughter cells formed are identical
to each other and identical to the mother
cell.
2n = 46
4n = 92
2n = 46
In Mitosis, each daughter cell is exactly
the same as the original mother cell.
What Happens After Mitosis?
The cell returns
to interphase
Chromosomes
uncoil back into
chromatin
The cycle
repeats itself
over & over…
Bacteria Reproduce via Binary Fission
Mitosis is also an ASEXUAL form
of reproduction. These are other
examples of the uses of mitosis to
create new organisms asexually:
Propogation of
plants by cuttings
Runners from
plants like
strawberries
Budding of Yeast