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8/3/2019 MITOSIS A&P I
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MITOSIS
Mitosis is the nuclear division
of somatic, or body cells.This process divides the
chromosomes found in the
nucleus. It results in two nuclei,which are identical.
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MITOSIS
Mitosis occurs in theM phase of the cell cycle.
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MITOSIS
Chromosomes were first
observed by Walter Fleming
in 1882. He was observingthe dividing cells of a
salamander larvae. It was
Fleming who first used theterm mitosis.
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CHROMOSOMES
Chromosomes are composed
of both DNA and histoneproteins. This complex of DNA
and histone proteins is about
50% DNA and 50% proteins.
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CHROMOSOMES
A typical human chromosome
contains about half billionnucleotides in one long DNA
helix that would be about 5
centimeters if laid out in astraight line.
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CHROMATIN-CHROMOSOMES
When our DNA-histone protein
molecule is long and uncoiled,it is termed chromatin. However,
when it becomes coiled and
condensed it is termed a chromosome.
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CHROMATIN-CHROMOSOMES
Chromatin is present during
interphase and the C phaseof the cell cycle. Chromosomes
are present during the M phase
of the cell cycle.
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CHROMOSOMES
Chromosomes exist in somatic
cells as two nearly identical
copies of each other calledhomologous chromosomes, or
homologues. Cells that have
two of each type of chromosomeare called diploid cells.
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CHROMOSOMES
During the s subphase of
interphase, each of the two
homologues chromosomesreplicate. This results in two
identical copies called sister
chromatids. The chromatidsare joined at a site called the
centromere.
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INTERPHASE
During interphase the cell is not dividing.
Interphase is divided into phases. G1 phase isthe time when the cell carries out basic
functions and performs specialized activities.The cell produces energy and grows. The
duration is extremely variable. This phasecontains a restriction checkpoint when the
cell “decides” to divide, enter a quiescentphase, G0 , or die.
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INTERPHASE
The G0 Phase can replace the G1 Phase ifthe cell maintains its specialized
characteristics, but does NOT divide.Examples of this in the human body
include neurons and muscle cells.
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INTERPHASE
S Phase - cell replicates
chromosomes &synthesizes proteins.
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INTERPHASE
G2 Phase –The cellsynthesizes additional
proteins and assemblesmembrane materials.Also the centriolesreplicate.
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MITOSIS
The process of mitosis occurs during theM Phase of the cell cycle. Mitosis is
one continuous event. However,for the ease of study it is
divided into 4 stages: prophase, metaphase, anaphase,
and telophase.
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PROPHASE
1. The chromatincondenses and forms areplicated chromosome.
2. The nuclear enevlopeopens.
3. The nucleolus degrades.
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PROPHASE
4. The centrioles migrateto opposite ends of thecell.
5. The mitotic apparatusforms from thecytoskeleton.
6. The replicatedchromosomes attach tothe spindle fibers usingtheir kinetochore fibers.
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METAPHASE
1. The replicatedchromosomes movetoward the center of themitotic apparatus.
2. The replicatedchromosomes alignthemselves in the centerof the mitotic apparatus.
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ANAPHASE
1. The centromere, whichis composed of twokinetochores, splits andthe sister chromatidsseparate.
2. The sister chromatids“travel” toward the polesof the mitotic apparatus.
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ANAPHASE
3. The cleavage
furrow begins to form.
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TELOPHASE
1. The sister chromatidsarrive at the poles of themitotic apparatus.
2. The mitotic apparatusis degraded and reformsthe cytoskeleton of thecell.
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TELOPHASE
3. The nuclear envelopereforms from the roughE.R.
4. The nucleolus reforms.
5. The chromosomes begin
to uncoil and lengthen toreform chromatin.
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CYTOKINESIS
Cytokinesis is the divisionof the cell’s cytoplasm after
mitosis. It results in two cells.
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CYTOKINESIS
1. The cleavage furrowdeepens using
microfilaments.
2. The contraction
continues until the cellis literally pinched intwo.
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Cytokinesis in
animal cells
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MITOSIS and CYTOKINESIS
Mitosis followed by cytokinesis leads toincrease in the number of cells, growth,with each cells having the same numberof chromosomes and the same genetic
information.
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CANCER
Cancer (loss of cell cycle control) is a
condition resulting from excess celldivision or deficient apoptosis.
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CANCER
Characteristics of Cancer Cells:
can divide uncontrollably
are heritable & transplantablelack contact inhibition
readily metastasize
exhibit angiogenesisexhibit genetic mutability
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CAUSES OF CANCER
1. Over-expression of oncogenesOncogenes are genes that trigger
limited cell division.2. Inactivation of tumor suppressor
genes
Tumor suppressor genes prevent a cellfrom dividing or promote apoptosis.