AP Biology Chapter 12: The Cell Cycle

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AP BiologyChapter 12The Cell Cycle
Omnis cellula e cellula (Every cell from a
cell) -Virchow
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Cell Division

• Basis of the continuity of life.
• Involves making new cells by pinching in half
  after distributing identical genetic material
  (DNA) to each daughter cell

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Basic Vocab

• Genome All the DNA of one cell
• Prokaryotes made of one long DNA molecule
• Eukaryotes made of many long DNA molecules
  (typical human cell has over 3m of DNA!!)
• Chromosome packages of DNA wound around
  proteins for easier organization
• Somatic Cell all body cells that are not sex
  cells. (humans 46 chromosomes)
• Gamete reproductive cells (sperm/eggs) have half
  the chromosomes of somatic cells (humans 23
  chromosomes)

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The Chromosome

• Chromatin long, thin DNA-protein complex.
  Becomes densely coiled around proteins in
  chromosomes
• Sister Chromatids Each duplicated chromosome has
  2 sister chromatids, each with identical DNA.
• Centromere Center, waist region of the
  chromosome where 2 sister chromatids are held
  together

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Cell Division

• Mitosis division of the nucleus. Yields 2
  identical daughter cells.
• Cytokinesis division of the cytoplasm
• Meiosis division which yields daughter cells
  with only ½ the DNA of the parentonly occurs in
  gametes.

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Mitotic Cell Cycle

• Cell Cycle life cycle of the cell as it lives
  and divides.
• Cell Cycle has 2 major phases
• Interphase 90 of the cycleCell grows, copies
  chromosomes, and prepares for division. Has 3
  main parts
• G1 First Gap
• S DNA Synthesis
• G2 Second Gap
• M Mitosis and Cytokinesis
• Has 6 parts
• Prophase, Prometaphase, Metaphase, Anaphase,
  Telophase, Cytokinesis

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Phases of MitosisG2 of Interphase

• Late Interphase
• The nucleus is well defined and has nuclear
  envelope with nucleoli
• Centrosomes have replicated and are together
• Asters or microtubules begin to extend from
  centrosomes
• Chromosomes have been duplicated, but cannot be
  seen because they are still in chromatin form

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Phases of MitosisProphase

• Chromatin fibers condense into chromosomes
  (tightly coiled). Appear as joined sister
  chromatids
• Nucleoli disappear
• Mitotic Spindle begins to form (microtubules
  extending from centrosomes)
• Centrosomes being to move to poles of cell

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Phases of MitosisPrometaphase

• Nuclear envelope fragments
• Spindle fibers interact with chromosomes
• Kinetochores form at the centromere of each
  chromosome to attach to spindle fibers
• Nonkinetochore fibers interact with those from
  the opposite pole.

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Phases of MitosisMetaphase

• Centrosomes are at opposite poles
• Chromosomes line up on Metaphase Plate, an
  imaginary line across the center of the cell
• Kinetochores are attached to 2 spindle fibers,
  one from each pole

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Phases of MitosisAnaphase

• Occurs suddenly, when paired sister chromatids
  separate into separate chromosomes
• Chromosomes are dragged, centromere first, toward
  opposite poles as kinetochore fibers shorten
• Nonkinetochore fibers lengthen, stretching the
  cell
• At the end of anaphase, there are identical,
  complete set of chromosomes at each pole

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Phases of MitosisTelophase

• Nonkinetochore fibers elongate
• Spindle fibers begin to break down
• Daughter nuclei being to form at the poles
• Nuclear envelopes arise
• Nucleoli form
• Chromatin fibers uncoil
• Mitosis is complete
• Cytokinesis begins to form a cleavage furrow and
  pinches the cell into two new cells

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Phases of MitosisCytokinesis

• Separation of the cytoplasm cleavage
• Occurs when actin microfilaments form a ring
  around the inside of the cell and pinch in to
  separate.
• Begins as a cleavage furrow or shallow groove in
  the cell membrane near old metaphase plate

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Cytokinesis in Plants

• Plants cannot pinch in because of cell walls
• Instead, they form a cell plate
• Vesicles containing cell wall materials and
  deposit at metaphase plate to build new wall and
  new membranes

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Binary Fission in Bacteria

• Prokaryotes only have one long circular bacterial
  chromosome
• Use binary fission or division in half as a
  rapid, easy way to divide
• Have no mitotic spindles
• DNA begins to replicate at the origin of
  replication
• Replicated parts move apart, toward poles
• Cell membrane pinches inward and a new cell wall
  is deposited

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Regulation of the Cell Cycle

• Checkpoints critical control point when stop and
  go-ahead signals. Found at G1,G2, and M phases
• G0 phase nondividing statemost of the cells in
  the human body are in this phase.

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Cellular Regulation

• Kinase enzymes that activate or inactivate
  proteins by phosphorylation
• Give the go-ahead signals at the checkpoints
• Cyclins proteins that fluctuate in concentration
  in the cell
• Cyclin-dependant Kinases (Cdks) called M-phase
  Promoting Factor (MPF)
• Triggers the cells passage past the G2
  checkpoint into the M phase
• After M phase, it switches itself off and
  destructs the cyclin

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Internal and External Regulation of the Cell
Cycle

• Internal
• APC Anaphase-Promoting Complex wait signal
  to assure all chromosomes are lined up and
  attached correctly before separating kinetochores
• External
• Growth Factors Protein released by certain body
  cells that stimulates other cells to divide.
• Density-Dependent Inhibition crowded cells stop
  dividing. Only divide when not touching their
  neighbor.
• Anchorage Dependance to divide, cells must be
  attached to a substratum (ECM of tissue)

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Cancer

• Cancer cells do not respond normally to control
  mechanisms. They divide excessively and invade
  tissues.
• Do not exhibit density-dependent inhibition
• Do not stop growing when growth factors are
  depleted
• Stop dividing at random points rather than normal
  checkpoints
• Will divide indefinitely (are immortal)

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Cancer

• Transformation when normal cells convert to
  cancer cells
• Tumor mass of abnormal cells
• Benign remain at the original sitedo not cause
  serious problems
• Malignant becomes invasive and impairs the
  function of an organ
• Metastasis spread of cancer to other locations
  within the body usually by entering the
  circulatory or lymph system

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Curing Cancer

• Removing benign tumors can prevent metastasis
• Chemotherapy or Radiation of metastasized tumors
• Uses high energy rays or toxic drugs that are
  especially harmful to quickly dividing cells
• Makes patient sick because it also kills healthy,
  fast-growing cells (hair, stomach linings, skin,
  etc.)