Mitosis and the Cell Cycle Date ______

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Mitosis and the Cell Cycle Date ______

• The Cell Cycle

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Introduction to Cell Division

• Life is handed down from one generation of
  organisms to the next in the form of cells.
• A unicellular organism reproduces by dividing in
  two
• Multi-cellular organisms begin life as a single
  cell a zygote
• Repeated cell division produces the many cells of
  the body.

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Introduction to Cell Division

• When a cell divides, it must pass on the genetic
  information needed for the new cells to function
• The DNA that is found in the chromosomes of the
  nucleus carries the genetic information.
• Mitosis is the process that produces two new
  nuclei with the same number and kinds of
  chromosomes as the original nucleus
• Mitosis ensures that each new cell inherits a
  complete set of the parent cells genetic
  information.

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Introduction to Cell Division

• Examples of uses of mitosis
•  
• Unicellular organism ? 2 organisms
• Fertilised egg cell ? multi-cellular organism
• Old cells ? new cells
• Repair of damaged tissue

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Introduction to Cell Division

• Each kind of cell has a typical life-span which
  begins when the cell is formed by division of the
  parent cell and ends when the cell itself divides
  or dies.
• Yeast cell 2 hours
• Amoeba a few days
• Human embryo cell 15-20 minutes
• Human adult cell 8 hours to 100 days

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Overview The Key Roles of Cell Division

• The continuity of life is based upon the
  reproduction of cells, or cell division
• Unicellular organisms reproduce by cell division
• Multicellular organisms depend on cell division
  for
• Development from a fertilized cell
• Growth
• Repair

20 µm
200 µm
(b) Growth and development. This micrograph
shows a sand dollar embryo shortly
after the fertilized egg divided, forming
two cells (LM).
(c) Tissue renewal. These dividing bone
marrow cells (arrow) will give rise to new
blood cells (LM).
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Cell Division Key Roles

• Genome cells genetic information
• Somatic (body cells) cells
• Gametes (reproductive cells) sperm and egg cells
• Chromosomes DNA molecules
• Diploid (2n) 2 sets of chromosomes
• Haploid (1n) 1 set of chromosomes
• Chromatin DNA-protein complex

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Cell Division Key Roles Cont
Chromatids replicated strands of a
chromosome Centromere narrowing waist of
sister chromatids Kinetochore The chromosomal
attachment point for the spindle fibers located
within the centromeres. Mitosis nuclear
division Cytokinesis cytoplasm
division Meiosis gamete cell division
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Packaging DNA
Structure of a chromosome interaction.
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The Cell Cycle

• Interphase (90 of cycle) G1 phase growth
  S phase synthesis of DNA G2 phase
  preparation for cell division
• Go phase Quiescence temporary/reversible
  state of rest
• Cellular senescence is the phenomenon where cells
  lose the ability to divide.

Mitotic phase Mitosis nuclear division
Cytokinesis cytoplasm division
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Mitosis

• Prophase
• Prometaphase
• Metaphase
• Anaphase
• Telophase

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Prophase

• Chromosomes visible
• Nucleoli disappear
• Sister chromatids
• Mitotic spindle forms
• Centrosomes move

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Late Prophase

• Nuclear membrane fragments
• Spindle interaction with chromosomes
• Kinetochore develops

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Metaphase

• Centrosomes at opposite poles
• Centromeres are aligned
• Kinetochores of sister chromatids attached to
  microtubules (spindle)

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Anaphase

• Paired centromeres separate sister chromatids
  liberated
• Chromosomes move to opposite poles
• Each pole now has a complete set of chromosomes

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Telophase

• Daughter nuclei form
• Nuclear envelopes arise
• Chromatin becomes less coiled
• Two new nuclei complete mitosis

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Mitosis in a Animal cells
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Mitosis in a Animal Cells continued
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Mitosis in a Plant Cells
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Cytokinesis

• Cytoplasmic division
• Animals cleavage furrow
• Plants cell plate

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Prokaryotes (bacteria)

• Reproduce by a type of cell division called
  binary fission
• The bacterial chromosome replicates
• The two daughter chromosomes actively move apart

Origin of replication
Cell wall
Plasma Membrane
E. coli cell
Bacterial Chromosome
Two copies of origin
Origin
Origin
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The sequential events of the cell cycleare
directed by a distinct cell cycle control system,
which is similar to a clock
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The clock has specific checkpointswhere the cell
cycle stops until a go-ahead signal is received
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Cell Cycle regulation

• Growth factors
• Density-dependent inhibition
• Anchorage dependence

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Cancer

• Transformation
• Tumor benign or malignant
• Metastasis