CELL DIVISION

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The Cell Cycle Mitosis Beyond
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THINK Of how many cells are you composed? 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 cells ever stop
dividing? Are all cells capable of division and
replacement?
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Why does a cell divide?

• As a cell absorbs nutrients and gets larger, the
  volume of the cell increases faster than the
  surface area.
• -Therefore, the demands of the cell (the volume)
  exceed the ability of the cell to bring in
  nutrients and export wastes. Solution? Divide
  into two smaller cells

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When is cell division occurring?
GROWTH -increase number of cells REPAIR -replace
lost cells due to injury, disease CANCER
Abnormally high rates of cell division due to
mutation Different kinds of cells divide at
different rates E. coli 20 minutes (What
domain?) Yeast cell 2 hours (What domain? What
kingdom?) Amoeba a few days (What domain? What
kingdom?) Human embryo cell 15-20 minutes Human
adult cell 8 hours to 100 days
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Aging
All cells die after a certain number of divisions
(programmed cell death-apoptosis). At any
given time some cells are dividing and some cells
are dying. Childhood Cell division gt
cell death Adulthood Cell division
cell death Aging Cell division lt cell death
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Control of the Cell Cycle Cell proliferation
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Interphase
Interphase 90 of the time. Ø   G1 Little new
cell absorbs nutrients and grows larger. Does
protein synthesis, its job. Ø   S phase
Synthesis of new DNA (DNA replication) for
daughter cells in preparation for mitosis. Ø  
G2 Cell continues to grow, do protein synthesis,
do its job. Gets too large, needs to divide.
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• Chromosomes exist in 2 different states, before
  and after they replicate their DNA. Before
  replication, chromosomes have one chromatid.
  After replication, chromosomes have 2 sister
  chromatids, held together at the centromere.
  Each chromatid is one piece of DNA with its
  supporting proteins.
• Remember that diploid cells have two copies of
  each chromosome, one from each parent. These
  pairs of chromosomes are NOT attached together.

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• Prior to cell division
• chromosomes (DNA) are replicated
• (duplicated)

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How long is one cell cycle? Depends. Eg. Skin
cells every 24 hours. Some bacteria every 2
hours. Some cells every 3 months. Nerve cells,
never. Cancer cells very short. Programmed cell
death Each cell type will only do so many cell
cycles then die. (Apoptosis)
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MITOSIS
Equal distribution of the 2 sets of DNA amongst
the 2 daughter cells. 4 Stages PMAT 1.
Prophase 2. Metaphase 3. Anaphase 4. Telophase
How the Cell Cycle Works Mitosis Animation Cell
Cycle
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What is Mitotic Cell Division?

• Division of somatic cells (body cells)
• (non reproductive cells) in
• eukaryotic organisms

• A single cell divides into two
• identical daughter cells
• (cellular reproduction)

gt Maintains chromosome ploidy of cell
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Ploidy refers to the number of pairs of
chromosomes in cells

• haploid one copy of each
• chromosome
• designated as n

• diploid two copies ( pair) of each
• chromosome
• designated as 2n

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As a 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.
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Prophase
 
-Chromatin condenses (coils) into chromosomes.
Sister chromatids joined by centromere.
-Nuclear membrane dissolves. -Centrioles divide
and move to opposite poles forming spindle
between them.
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Metaphase
-Sister chromatids line up on metaphase
plate. -Centromeres lock on to spindle fibre
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Anaphase
-Centromeres divide. -Spindle fibres contract
pulling sister chromatids apart to poles.
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Telophase-New nuclear membranes form around
new nuclei
Mitosis Movie
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CYTO KINESIS Cytoplasm splits into 2 cells.
-Animal cells Cleavage furrow forms from
outside in. - Plant cells Division/cell plate
forms from inside out.  
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Cell now returns to interphase . The chromosomes
uncoil back into chromatin. The whole cell cycle
starts over again..
http//www.cellsalive.com/mitosis.htm
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At any point in time the cells in a tissue will
be at different stages in the cell cycle.
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Mitosis Stages Put these in the correct order..
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The Guarantee of Mitosis

• The 2 daughter cells formed are identical to each
  other and identical to the mother cell.
• Why is this so important?

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In Mitosis, each daughter cell is exactly the
same as the original mother cell. Cell
Differentiation
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Budding of Yeast
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
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Homologous pairs of chromosomes
Each chromosome has a certain gene sequence on
it. Eg. Chrom 1 Has insulin, foot size, and
lactase on it. You have a chromosome one from
your mom and one from your dad. So you have 2
genes for each trait. One from your mom one
from your dad. A homologous pair is a pair
with the same gene sequence one from mom, one
from dad.
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Cancer

• Cancer is a disease of uncontrolled cell
  division. It starts with a single cell that
  loses its control mechanisms due to a genetic
  mutation. That cell starts dividing without
  limit, and eventually kills the host.
• Normal cells are controlled by several factors.
  They stay in the G1 stage of the cell cycle until
  they are given a specific signal to enter the S
  phase, in which the DNA replicates and the cell
  prepares for division. Cancer cells enter the S
  phase without waiting for a signal.
• Another control normal cells are mortal. This
  means that they can divide about 50 times and
  then they lose the ability to die. This clock
  gets re-set during the formation of the gametes.
  Cancer cells escape this process of mortality
  they are immortal and can divide endlessly.
• A third control cells that suffer significant
  chromosome damage destroy themselves due to the
  action of a gene called p53. Cancer cells
  either lose the p53 gene or ignore its message
  and fail to kill themselves.

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• Many Mutations Lead to Cancer
• All cancer is genetic, in that it is triggered by
  altered genes. Genes that control the orderly
  replication of cells become damaged, allowing the
  cells to reproduce without restraint.
• Cancer usually arises in a single cell. The
  cell's progress from normal to malignant to
  metastatic appears to follow a series of distinct
  steps, each controlled by a different gene or set
  of genes.

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• Even though all cancer is genetic, just a small
  portionperhaps 510 is inherited.
• Most cancers come from random mutations that
  develop in body cells during one's
  lifetimeeither as a mistake when cells are going
  through cell division or in response to injuries
  from environmental agents such as radiation or
  chemicals.

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• Cancer cells contain several (6-8) mutated genes.
  These almost always include
• mutations in genes that are involved in mitosis
  (oncogenes tumor suppressor genes)
• Genes that regulate apoptosis
• Genes that maintain telomeres
• Genes that stimulate angiogenesis
• Metastasis genes
• Genetic Therapy Breast Tumors

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Cancer Progression

• There are many different forms of cancer,
  affecting different cell types and working in
  different ways. All start out with mutations in
  specific genes called oncogenes. The normal,
  unmutated versions of the oncogenes provide the
  control mechanisms for the cell. The mutations
  are caused by radiation, certain chemicals
  (carcinogens), and various random events during
  DNA replication.
• Once a single cell starts growing uncontrollably,
  it forms a tumor, a small mass of cells. No
  further progress can occur unless the cancerous
  mass gets its own blood supply. Angiogenesis
  is the process of developing a system of small
  arteries and veins to supply the tumor. Most
  tumors dont reach this stage.
• A tumor with a blood supply will grow into a
  large mass. Eventually some of the cancer cells
  will break loose and move through the blood
  supply to other parts of the body, where they
  start to multiply. This process is called
  metastasis. It occurs because the tumor cells
  lose the proteins on their surface that hold them
  to other cells.

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Cancer Treatment

• Two basic treatments surgery to remove the
  tumor, and radiation or chemicals to kill
  actively dividing cells.
• It is hard to remove all the tumor cells. Tumors
  often lack sharp boundaries for easy removal, and
  metastatic tumors can be very small and anywhere
  in the body.
• Radiation and chemotherapy are aimed at killing
  actively dividing cells, but killing all dividing
  cells is lethal you must make new blood cells,
  skin cells, etc. So treatment must be carefully
  balanced to avoid killing the patient.
• Chemotherapy also has the problem of natural
  selection within the tumor. If any of the tumor
  cells are resistant to the chemical, they will
  survive and multiply. The cancer seems to have
  disappeared, but it comes back a few years later
  in a form that is resistant to chemotherapy.
  Using multiple drugs can decrease the risk of
  relapse.

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Resources

• Mitosis ? CANCER
• http//www.biology.iupui.edu/biocourses/N100H/ch8m
  itosis.html
• http//www.schoolscience.co.uk/content/4/biology/a
  bpi/cancer/cancer3.html
• http//www.schoolscience.co.uk/content/4/biology/a
  bpi/cancer/cancer3.html
• http//genetics.gsk.com/chromosomes.htm
• http//www.horton.ednet.ns.ca/staff/selig/handouts
  /bio12/cellrepro/cancermitosis.pdfsearch2222ca
  ncer20animation2220mitosis22
• How Cancer grows http//www.pbs.org/wgbh/nova/canc
  er/grow_flash.html
• Mitosis http//pages.csam.montclair.edu/smalley/
  mitosis.mov
• http//faculty.pingry.org/thata/pingry_upload/movi
  es/cellular_reproduction/plantcell_lily_mitosis.mo
  v
• http//www.zo.utexas.edu/faculty/delozanne/celldiv
  ision/Mitosis20Video.mov
• Cell Cycle Cancer Animations
  http//science.education.nih.gov/supplements/nih1/
  cancer/activities/activity2_animations.htm
• Cell Biology Cancer Animations
  http//www.learner.org/channel/courses/biology/uni
  ts/cancer/images.html
• Mitosis Meiosis Interactive Exercise
  http//biologyinmotion.com/cell_division/
• Mitosis Animations http//www.sci.sdsu.edu/multim
  edia/mitosis/navigator.html
• Plant Cell Mitosis http//www.teachersdomain.org/
  resource/tdc02.sci.life.stru.dnadivide/