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IB BIOLOGY
CELL DIVISION
MITOSIS:
Mitosis is the process by which a cell divides and produces
two daughter cells from a single parent cell.
http://www.johnkyrk.com/mitosis.html
animation
http://www.youtube.com/watch?v=lf9rcqifx34
Cell cycle.
http://www.youtube.com/watch?v=8LhQllh46yI
Cell how does it become cancerous
FUNCTIONS OF MITOSIS:
Mitosis is used in eukaryotes whenever genetically
identical cells are needed.
1. During growth. Cell divisions in the root tip produces
new cells, which elongate to bring about growth of the
root.
2. Cell replacement: Mitotic cell division within the red
marrow of your body’s bones (particularly within your
ribs, vertebrae, breast bones and pelvis) continuously
create new blood cells that replace older ones.
3. When tissues have been damaged and need to be
repaired. Dividing cells within your epidermis
continuously replace dead cells that slough off the
surface of your skin.
4. To reproduce asexually: Hydra is a multicellular
organism which can reproduce both sexually and
asexually. It reproduces asexually by budding. A bud
starts as a mass of mitotically dividing cells growing
on the side of the parent. The bud develops into a
small hydra.. Eventually the offspring detaches from
the parent and takes up life on its own.
In all these cases stated above, the new cells have exactly
the same number and types of chromosomes as the
parent cells because of the day the duplicated
chromosomes divide during mitosis.
If a human skin cells with 46 chromosomes divides by
mitosis, each daughter cells will have ----------chromosomes.
STAGES IN CELL CYCLE:
Cell cycle, is an ordered sequence of events that extends
from the time a cell is first formed from a dividing parent
cell until its own division into two cells. The cell cycle
consists of two broad stages:
A growing stage (called interphase), during which the cell
roughly doubles everything in its cytoplasm and precisely
duplicates its chromosomal DNA, and
the actual cell division (called the mitotic phase).
INTERPHASE:
The longest part of the cell cycle in most cells is interphase.
This is the time when the cell’s metabolic activity is high.
The cell in interphase increases its supply of proteins,
creates more cytoplasmic organelles (such as mitochondria
and ribosomes) and grow in size. The chromosomes
duplicate during this period.
Interphase lasts for at least 90% of the total time required
for the cell cycle.
Interphase can be divided into three subphases.
1. The G1 phase (“first gap”)
2. the S phase and
3. the G2 phase (“second gap)
The major event during interphase is growth.
Events of interphase
Phases of interphase
Major events
G1
Growth of cell and increase
in number of organelles.
S
G2
Overall
Continues to grow.
Replication of
chromosomes with copies
remaining attached to one
another
Further growth occurs,
organelles increase in
number, DNA condenses to
form visible chromosomes,
microtubules begin to form.
The cell is performing the
tasks appropriate to its type.
The mitotic phase: It is the part of the cell cycle when the
cell actually divides, accounts for only 10% of the total
time required for the cell cycle.
The mitotic phase is divided into two stages called mitosis
and cytokinesis although the second stage begins before
the first phase ends.
In mitosis, the nucleus and its contents, including the
duplicated chromosomes, divide and are evenly distributed
to from two daughter nuclei.
During cytokinesis, the cytoplasm is divided into two.
The combination of mitosis and cytokinesis produces two
genetically identical daughter cells, each with a single
nucleus, and plasma membrane.
Each newly produced daughter cell may then proceed
through G1 and repeat the cycle.
Cancer, is the disease of the cell cycle. Cancer cells do not
respond normally to the cell cycle control system, they
divide excessively and can invade other tissues of the body.
If unchecked , cancer cells may continue to grow until they
can kill the organism.
The abnormal behavior of cancer cell begins when a single
cell undergoes transformation, a process that converts a
normal cell to cancer cell. The body’s immune system
recognizes a transformed cell as abnormal and destroys it.
If the cell evades destruction, it may proliferate to form a
tumor, an abnormally growing mass of body cells. If the
abnormal cells remain at the original site, the lump is called
a benign tumor. Benign tumor cells can cause problems if
they grow in and disrupt certain organs, such as the brain,
but they can often be completely removed by surgery.
In contrast , a malignant tumor can spread into neighboring
tissues and other parts of the body, displacing normal tissue
and interrupting organ functions.
The spread of the cancer cells via the circulatory system
beyond their original site is called metastasis.
1. Structure
Normal Cells
Cancer Cells
DNA in genes and
chromosomes go about
their business in a
normal way.
Cancer cells develop a
different DNA or gene
structure or acquire
abnormal numbers of
chromosomes.
Cells continue to be
Cells divide in an orderly created without control
way to produce more
or order. If not needed,
cells only when the body a mass of tissue is
needs them.
formed, which is called a
tumor
2. Energy
Normal Cells
Cancer Cells
Cells have a defective
Cells derive 70% of their
"Krebs Cycle" and
energy from a system
derive little or no energy
called the "Krebs Cycle.
from it
Cells derive only 20% of
Cancer cells derive
their energy from a
almost all their energy
system called
from "Glycolysis."
"Glycolysis."
Cells derive most of
Cells derive most of
their energy with the use their energy in the
of oxygen.
absence of oxygen.
3. Blood Vessels
Normal Cells
Cancer Cells
Cells have a built-in
blood vessel system.
Cells don’t have a builtin blood vessel system.
They require more of
certain amino acids to
build one.
4. Growth Factors
Normal Cells
Cancer Cells
While similar to cancer
cells, the amount of
them are more in
balance to produce a
more normal level of
activity.
These cells have over
produced, require more
chemicals (food) and
are over active
5. Functions
Normal Cells
The enzymes and
hormones go about
business in a normal
balanced manner.
Cancer Cells
The enzymes and
hormones are either
over active or under
active.
Tumors Are Different
Benign
Benign tumors are not
Malignant
Malignant tumors are
cancerous. They do not
invade nearby tissues
nor spread to other parts
of the body. They can
be removed and are not
a threat to life.
cancerous. They can
invade and damage
nearby tissues and
organs, and they can
break away and enter
the blood stream to form
new tumors in other
parts of the body. The
spread of cancer is
called metastasis.
During the growth phase, G2, the chromatin
(elongated DNA and histones) begins to condense.
This condensation is accomplished by the process
called supercoiling.
First the DNA wraps around histones to produce
nucleosomes.
The nucleosomes are further wrapped into a
solenoid.(coil of nucleosomes)
Solenoid group together in looped dmomains, and
then a final coiling occurs to produce the
chromosome.
Eukaryotic cells contain chromosome which, before
replication in the S phase of the cell cycle, are
composed of one molecule of DNA. After replication,
the chromosome includes two molecules of DNA.
These two identical molecules are held together by
the centromere, and each molecule is referred to as a
chromatid. Together they are called sister chromatids.
The chromatids will eventually separate during the
process of mitosis. When they do each is then called
a chromosome and each has its own centromere.
MITOSIS:
Mitosis involves four stages:
Prophase, metaphase, anaphase, and telophase.
The process occur in continuum. We only use the
separate stages to understand the overall process.
Prophase:
1. During prophase , changes occur in both the nucleus
and cytoplasm.
2. Within the nucleus, the chromatin fibers become more
tightly coiled and folded forming discrete
chromosomes.
3. The nuclear envelope disintegrates and nucleoli
disappear.
4. Each duplicated chromosome appears as two identical
sister chromatids joined together , at the centromere.
The centromere of each chromosome has a region
called kinetochore that attaches to the spindle.
5. In the cytoplasm, the mitotic spindle begins to form as
microtubules rapidly grow out from the centrosomes,
which begin to move away from each other(the
centrosomes move toward opposite poles of the cell due
to lengthening microtubules.)
6. The spindle is complete at the end of prophase.
METAPHASE:
1. At metaphae the spindle is completely formed with its
poles at the opposite ends of the cell.
2. The chromosomes are moved to the middle or equator
of the cell.This is referred to as the metaphase plate.
3. The centromere of all the chromosomes are lined up on
the metaphase plate.
4. The movement of the chromosomes is due to the action
of the spindle which is made of microtubules.
5. The centrosomes are now at the opposite poles.
ANAPHASE:
1. This is usually the shortest phase of mitosis. It begins
when the sister chromatids of each chromosome are
split.
2. These chromatids, now chromosomes, move toward the
opposite poles of the cell.
3. The chromatid movement is due to shortening of the
microtubules of the spindle.
4. Because the centromeres are attached to the
microtubules, they move towards the poles first.
5. At the end of this phase, each pole of the cell has a
complete, identical set of chromosomes.
TELOPHASE:
Telophase is roughly the reverse of prophase.
1. The chromosomes are at each pole.
2. A nuclear membrane (envelope) begins to re-form
around each set of chromosomes.
3. The chromosomes start to elongate to form chromatin.
4. Nucleoli reappear.
5. The spindle apparatus disappear.
6. The cell is elongated and ready for cytokinesis.
CYTOKINESIS:
Once the process of nuclear division has occurred the cell
undergoes cytokinesis.
In animal cells cytokinesis involves an inward pinching of
the fluid plasma membrane to form cleavage furrows.
Plant cells have a relatively firm cell wall and they form
cell plate. The cell plate occurs midway between the two
poles of the cell and moves toward the sides of the cell
from the central region.
Both process result in two separate daughter cells that
have genetically identical nuclei.
http://www.nclark.net/MitosisLab.pdf