Cell Cycle

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Cell Cycle

• Cell growth and reproduction.

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Surface to Volume Ratio

• The ratio or proportion of surface area to
  internal volume is limited and this limits how
  large a cell can become.

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Cell Size is Limited

• By surface area can only take in a limited
  amount of materials by diffusion.
• By DNA can only direct a limited amount of cell
  activities.

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Why do cells divide?

• During reproduction
• Replace damaged or dead cells
• Growth after fertilization.

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When do they divide?

• When stimulated by growth factors.
• GROWTH FACTORS- mostly protein signals.
• GO/NO GO switch is during G1 of cell cycle.

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Cell Cycle
Events in the growth, development
and reproduction of the cell. Go cells have
stopped dividing or have lost the potential to
divide.
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G2
P
M
S
A
T
Cytokinesis
G1
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G1- gap or growth after cell division. Cell
grows in size. S- synthesis of new DNA from
existing template (chromosome replication) G2-
gap 2 or growth prior to cell division
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• M- mitosis or chromosome division
• C- cytokinesis or cell division

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Interphase is non-dividing

• Interphase G1, S, and G2

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Chromosomes

• In Eukaryotes
• Chromosomes organize and carry the DNA during
  cell division.

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Chromosome- same as chromatid

• A chromatid is made of DNA and a protein. They
  have a centromere in the center for spindle
  attachment.
• centromere

DNA
chromatid
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Chromosomes
DNA is continuous and wound around protein which
is coiled and super coiled into a dark staining
body. Chromosomes can be seen as having two arms
and often one is longer.
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chromatid
centromere
Sister chromatid
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Chromosome Number is fixed in each species
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Mitosis Animation

• http//www.cellsalive.com/mitosis.htm

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Interphase
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Prophase
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Metaphase
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Anaphase
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Telophase
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interphase
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prophase
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prophase
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metaphase
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anaphase
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telophase
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telophase
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telophase
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Initiate Mitosishttp//faculty.plattsburgh.edu/d
onald.slish/Anaphase20transitionII.html

• Molecular motors in Mitosis
• http//faculty.plattsburgh.edu/donald.slish/Motors
  .html
• Asters http//faculty.plattsburgh.edu/donald.slish
  /astralII.htm

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Microtubules motors attached to the kinetochores
to move them Toward the minus end of shrinking
microtubules (a dynein). Toward the plus end
of lengthening microtubules (a kinesin). The
chromosome arms use a different kinesin to move
to the metaphase plate. . The sister
kinetochores separate, carrying their attached
chromatid. powered by minus-end motors, dyneins,
while the microtubules themselves shorten
(probably at both ends).
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2. The overlapping non-kinetochore spindle
fibers move past each other (pushing the poles
farther apart) powered by plus-end motors, the
"bipolar" kinesins.
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prophase- centrioles migrate, aster form,
chromosomes condense, nucleolus nucleus
disappear, mitotic spindle forms.
Centrosome-tubule organizing center.
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Prometaphase ( prophase)- bundles of microtubules
migrate to poles while spindles form and attach
to centromere
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Metaphase- chromosomes are on equator( center)
Centrioles are at opposite poles
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Anaphase- paired centromeres of each chromosome
divide and sister chromatids move towards
opposite poles. Cell begins to elongate.
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Telophase- microtubles elongate the cell even
more. The nucleus and nucleoli begin to reform.
Cytokinesis begins.
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kinetochore


Non-kinetochore
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Cytokinesis

• Animal cells- constriction ring of microfilaments
  on the inside of membrane creates a cleavage
  furrow.
• Plant cells- vesicles align at metaphase plate
  and fusion of vesicles creates cell membranes
  which give rise to cell plate.

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Cell Cycle Clock

• Rhythmic changes in the molecules that regulate
  the cell cycle.
• Proteins regulate the cell clock

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KINASE PROTEINS

• -enzymes which activate other proteins by
  phophorylating them

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CYCLIN

• Proteins which combine with kinase proteins to
  activate them
• Cdks-cyclin dependent kinases

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MGrowth Factors

• MPF- Mitogen or Maturation Promoting Factor
• Stimulates the Mitotic Cycle in many ways (
  mostly by phosphorylating various kinase
  proteins)
• A cyclin dependent complex
• Levels Fluctuate
• Breaks cyclin down

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How it works

• Cyclin dependent kinase, Cdks, are in constant
  circulation
• They are activated when the attach to cyclin
• Once activated they promote some aspect of
  mitosis
• ex. Synthesis of DNA
• spindle elongation and attachment
• They also catalyze the breakdown of Cyclin

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Changes in Cyclin

• http//faculty.plattsburgh.edu/donald.slish/MPF.ht
  ml

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Stem cells

• (Unspecialized ) Can become other cells
• Can renew themselves through repeated cell
  division

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Types of Stem Cells

• Totipotent- can produce any type of cell
• source-newly fertilized egg-blastocyst
• Pluripotent-can produce a variety of tissue types
  but not all
• Source-HSC (hematopoietic stem cells) adult bone
  marrow

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Stem cells

• Used to treat disease
• Parkinsons disease.
• Spinal Cord Injury
• Heart disease
• Loss of Body Parts

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Embryonic Stem Cells

• ESC- can produce all the different types of cells
  that make up our bodies
• Source inner cell mass of a blastocyst (
  5 days following fertilization)

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Adult Stem Cells

• Cells which retain some ability to form many type
  of tissues
• source-mostly bone marrow, although other
  sources are being investigated
• Umbilical Cord Cells
• Placental cells and those of the
  Amniotic Fluid

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Normal Cells

• Adhesive stick together
• Anchorage dependence- must be attached to other
  cells
• Contact inhibition- cells prevent their neighbors
  from dividing by proteins or enzymes that control
  the cell cycle

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Cancer cells

• Lost adhesiveness( anchorage dependence)
  metastasis ( move throughout body)
• Lost contact inhibition- neighboring cells no
  longer exhibit control
• compete with normal healthy cells

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Single cell origin

• Cancer tumors begin as a single cell
• Tumor suppressor genes prevent this.

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Causes of Cancer

• Genetic- cancer occurs because of mutations in
  genes that control the cell cycle or cell clock.
• Requires multiple HITS

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Carcinogens

• Environmental factors that can induce or cause a
  mutation leading to cancer.
• Radiation ex. X rays
• Ultraviolet light ex. Sunlight
• Chemical Carcinogens ex. PCBs, nicotine, benzene.

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Not a Single Event

• Accumulated damage to genes
• ( MULTIPLE HITS )
• This means that it may take several exposures to
  a carcinogen or not depending on your genetic
  make-up

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Cancer Trends

• Cancer cluster- group with a higher rate for some
  form of cancer
• Cancer rates are related more to where your live
  not where you are from

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Klinefelters Syndrome
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Anaphase
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