THE REPRODUCTION

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• CHAPTER 11
• THE REPRODUCTION
• OFCELLS

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Mitosis

• Cells divide to make more cells. While all the
  other organelles can be randomly separated into
  the daughter cells, the chromosomes must be
  precisely divided so that each daughter cell gets
  exactly the same DNA.
• Mitosis is normal cell division, which goes on
  throughout life in all parts of the body.
  Meiosis is the special cell division that creates
  the sperm and eggs, the gametes.
• Mitosis and meiosis occur in eukaryotes.
  Prokaryotes use a different methodfission to
  divide.
• Humans have 46 chromosomes, 23 from each parent.
  Every cell has the same 46 chromosomes Each
  species has a characteristic number of
  chromosomes corn ahs 20, house flies have 10,
  chimpanzees have 48.

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Chromosomes

• The essential part of a chromosome is a single
  very long strand of DNA. This DNA contains all
  the genetic information for creating and running
  the organism.
• The DNA is packaged by proteins bound to it. At
  different times, these proteins cause the DNA to
  be spread out like spaghetti in a bowl, or
  tightly condensed into the X-shaped chromosomes
  we can see in the microscope.
• Chromosomes have
• Chromatids
• Centromere

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More Chromosomes

• Before replication, chromosomes have one
  chromatid.
• After replication, chromosomes have 2 sister
  chromatids, held together at the centromere
• In mitosis, the two chromatids of each chromosome
  separate, with each chromatid going into a
  daughter cell.
• 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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Cell Cycle

• Some cells divide constantly (cells in the
  embryo, skin cells, gut lining cells, etc.)
  Other cells divide rarely or never only to
  replace themselves.
• Actively dividing cells go through a cycle of
  events that results in mitosis. Most of the
  cycle was called interphase (the cell increases
  in size, but the chromosomes are invisible.)
• The 3 stages
• G1 (Gap) is the period between mitosis and S,
  when each chromosome has 1 chromatid. It is the
  time when the cell grows and performs its normal
  function. The S phase (Synthesis) is the time
  when the DNA is replicated, when the chromosome
  goes from having one chromatid to having 2
  chromatids held together at the centromere.
• G2 is the period between S and mitosis. The
  chromosome have 2 chromatids, and the cell is
  getting ready to divide.

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Machinery of Mitosis

• The chromosomes are pulled apart by the spindle,
  which is made of microtubules. They attach to
  each centromere, and anchored on the other end to
  centrioles.
• There are 2 centrioles, one at each end of the
  spindle. The chromosomes are lined up between
  the poles of the spindle.
• When they contract, the chromosomes are pulled to
  the opposing poles.

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Prophase

• In prophase, the cell begins the process of
  division.
• 1. The chromosomes condense (long thin to
  short fat).
• 2. The nuclear envelope disappears.
• 3. The centrioles move to opposite poles.
  During interphase, the pair of centrioles were
  together just outside the nucleus.
• 4. The spindle starts to form, growing out of the
  centrioles towards the chromosomes.

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Kinetochore vs Nonkinetochore

• Kinetochore protein structure located at
  centromere regions
• Kinetochore microtubules attach to the
  kinetochores!! (PULL CHROMOSOMES)
• Nonkinetochore microtubules overlap with
  nonkinetochore microtubules from the opposite
  pole. (ELONGATE CELL)

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Metaphase

• chromosomes line up on the equator (metaphase
  plate) of the cell, with the centrioles at
  opposite ends and the spindle fibers attached to
  the centromeres.
• Entire structure nonkinetochore microtubules
  kinetochore microtubules spindle

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Anaphase

• In anaphase, the centromeres divide.
• At this point, each chromosome goes from having 2
  chromatids to being 2 chromosomes, each with a
  single chromatid.
• Then the spindle fibers contract, and the
  chromosomes are pulled to opposite poles.

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Telophase

• Nonkinetochore microtubules elongate the cell
• The spindle disintegrates
• The nuclear envelope re-forms around the two sets
  of chromosomes.
• Daughter nuclei begin to reform
• The cytoplasm divides into 2 separate cells.

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Cytoplasmic Division

• The organelles (other than the chromosomes) get
  divided up into the 2 daughter cells passively
  they go with whichever cell they find themselves
  in.
• Plant and animal cells divide the cytoplasm in
  different ways.
• In plant cells, a new cell wall made of cellulose
  forms between the 2 new nuclei, about where the
  chromosomes lined up in metaphase. Cell
  membranes form along the surfaces of this wall.
  When the new wall joins with the existing side
  wall, the 2 cells have become separate.
• In animal cells, a ring of actin fibers
  (microfilaments are composed of actin) forms
  around the cell equator and contacts, pinching
  the cell in half.

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Summary of Mitosis

• Prophase
• Chromosomes condense
• Nuclear envelope disappears
• Centrioles move to opposite sides of the cell
• Spindle forms and attaches to centromeres on the
  chromosomes
• Metaphase
• Chromosomes lined up on equator of spindle
• Centrioles at opposite ends of cell
• Anaphase
• Centromeres divide each 2-chromatid chromosome
  becomes two 1-chromatid chromosomes
• Chromosomes pulled to opposite poles by the
  spindle
• Telophase
• Chromosomes de-condense
• Nuclear envelope reappears
• Cytoplasm divided into 2 cells

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PLANT vs ANIMAL

• PLANT CELL ANIMAL CELL
• Cell plate Cleavage furrow

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REGULATION OF THE CELL CYCLE

• GROWTH FACTORS occur in the presence of a wound
  cells respond and grow
• DENSITY-DEPENDENT INHIBITION Cells grow
  depending on the density of cells.
  (nutrients/space/adhesion)
• RESTRICTION POINT go/no go decision. If all
  systems are go (all external and internal
  conditions are favorable), the step proceeds.
• G0 phase nondividing state.

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• Cyclins concentrations fluctuate cyclically
• Cdk complex called MPF (maturation promotion
  factor (M-phase promoting factor)
• Near end of M-phase, MPF switches off by
  activating an enzyme that destroys cyclin.
• 1. cyclin is synthesized through the cycle and
  accumulates during interphase
• 2. cyclin attaches to Cdk and the protein complex
  is activated at the end of interphase
• 3. MPF coordinates mitosis by phosphorylating
  varous proteins, including other protein kinases
• 4. MPF is a cyclin-dependent kinase enzyme that
  destroys MPF activity.
• The Cdk component of MPF is recycled, its kinase
  activity restored by association with new cyclin
  that accumulates during interphase.

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Prokaryotic Cells Binary Fission

• Division in half
• Most bacterial genes are carried on a single,
  circular chromosome associated proteins.
• Replicates
• Attaches to different parts of the cell membrane
• Cell pulls apart and the replicate and original
  chromosomes are separated.

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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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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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MITOSIS LAB