The Cell Cycle and Mitosis

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Chapter 12

• The Cell Cycle and Mitosis

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The Key Roles of Cell Division

• Cell division functions in reproduction, growth,
  and repair
• Unicellular organisms (ex. Amoeba) will divide to
  reproduce entire organisms
• Cell division also will allows a multicellular
  organism to develop from a single cell

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The Key Roles of Cell Division

• DNA is passed from one generation of cells to the
  next without dilution.
• -cell duplicates it DNA
• - moves the 2 copies to opposite ends of the
  cell
• - and then splits into 2 daughter cells

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The Key Roles of Cell Division
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Concept 12.1

• Cell Division distributes identical sets of
  chromosomes to daughter cells
• A cells genetic material is called its genome
• - prokaryote single long DNA strand
• - eukaryote number of DNA molecules

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Concept 12.1

• The replication and distribution of DNA is
  manageable because it is packaged into
  chromosomes
• - the nuclei in human somatic cells contain 46
  chromosomes
• - the nuclei in human gametes contains 23
  chromosomes

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Concept 12.1
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Concept 12.1

• The DNA-protein complex is called the chromatin
  and is a long thin fiber.
• After the chromatin is duplicated, it will
  prepare for division. It will condense and coil
  up to form chromosomes.

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Concept 12.1

• Each duplicated chromosome has 2 sister
  chromatids.
• - each contains identical copies of the
  chromosomes DNA molecule
• - they are connected together at the centromere

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Concept 12.1
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Concept 12.2

• The mitotic phase alternates with interphase in
  the cell cycle
• The mitotic (M) phase (mitosis and cytokenesis)
  is the shortest part of the cell cycle.
• Interphase accounts for about 90 of the cell
  cycle.

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Concept 12.2

• Interphase can be divided into subphases
• - G1 (first gap), S (synthesis), and G2 (second
  gap)
• - during subphases, cell grows by producing
  proteins and organelles
• - chromosomes are only duplicated during the S
  phase

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Concept 12.2
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Concept 12.2

• Mitosis is broken down into 4 subphases
• - prophase, metaphase, anaphase, and telophase
• Prophase
• - chromatin coil into chromosomes
• - nucleoli disappears
• - spindles begin to appear as centrosomes move
  to the poles of the cell

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Concept 12.2

• The cell moves into prometaphase
• - nuclear envelope fragments
• - kinetochore attaches to forming spindles
• - cell prepares for metaphase

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Concept 12.2
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Concept 12.2

• Metaphase
• - centrosomes area at opposite poles
• - chromosomes are on equator of cell, the
  metaphase plate
• Anaphase
• - begins when the centromeres of the chromosomes
  separate

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Concept 12.2

• - sister chromatids begin moving toward opposite
  poles
• - by the end, the poles have equal sets of
  chromosomes
• Telophase
• - daughter nuclei form at the poles
• - nuclear envelope begins to reform

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Concept 12.2

• - chromosomes become less tightly coiled
• -Cytokenesis, the division of the cytoplasm,
  follows immediately

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Concept 12.2
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Concept 12.2

• The mitotic spindle distributes chromosomes to
  the daughter cells
• -during interphase, the single centrosome
  replicates to form 2 centrosomes during the
  early stage of mitosis, they separate and move
  toward opposite poles helping the spindle fibers

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Concept 12.2
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Concept 12.2

• Cytokenesis divides the cytoplasm
• - in animals, cytokenesis occurs by the
  formation of a cleavage furrow
• - in plants the cleavage cannot occur because of
  the cell wall vesicles will move to the center
  of the cell to form the cell plate.

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Concept 12.2
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Concept 12.2

• The origins of mitosis are believed to be from
  bacterial organisms of cell reproduction
• - prokaryotes reproduce by binary fission
  (dividing in half)
• - prokaryotes do not have mitotic spindles
  instead, once the DNA replicates, the copies of
  the region move apart rapidly

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Concept 12.2
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Concept 12.3

• The cell cycle is driven by specific chemical
  signals present in the cytoplasm
• Sequential events of the cell cycle are directed
  by a distinct cell cycle control system
• - driven by a built in clock
• - the cell cycle is regulated at certain
  checkpoints by internal and external controls

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Concept 12.3
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Concept 12.3

• The checkpoint is a control point where stop and
  go-ahead signals can regulate the cycle
• - kinases, a type of regulatory protein that
  activate or inactivate other proteins, give the
  signals for G1 and G2 checkpoints

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Concept 12.3

• To be active the kinase must be attached to a
  cyclin (kinases become cyclin-dependent kinases
  or Cdks)
• - the activity of Cdks rises and falls with
  changes in the cyclin
• - first called MPF maturation promoting
  factor or M-phase-promoting factor

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Concept 12.3

• - when cyclins accumulate during G2, MPF
  initiates mitosis
• Internal and external cues help regulate the cell
  cycle
• - for cells to divide a growth factor, a
  specific protein, is released to stimulate cell
  division

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Concept 12.3
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Concept 12.3

• The discovery of growth factors has led us to
  understand density-dependent inhibition of cell
  division
• - when a cell population reaches a certain
  density, the amount of growth factors and
  nutrients needed for division becomes
  insufficient for increased growth

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Concept 12.3

• Most animal cells also exhibit anchorage
  dependence
• - to divide, the cell must be attached to a
  substratum (ex. inside of a culture jar or
  extracellular matrix of a tissue)

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Concept 12.3
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Concept 12.3
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Concept 12.3

• Cancer cells have escaped from cell cycle
  controls
• - they do not respond to the control mechanisms
• - they do not stop dividing when growth factors
  are depleted dont respond to density dependant
  inhibition

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Concept 12.3

• - if cancer cells stop dividing, it is at random
  points and not at the checkpoints
• Caner begins when a single cell tissue undergoes
  a transformation
• - if the cell evades destruction by the immune
  system it may form a tumor

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Concept 12.3

• - if the abnormal cell remain at the original
  site, it is called a benign tumor
• - a malignant tumor becomes invasive enough to
  impair the functions of organs
• - the spread of cancer cells from the original
  site is called metastasis

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Concept 12.3
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Concept 12.3