Cell Division

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Cell Division

• Breaking Up Is Hard To Do!

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Cell Division

• The growth and splitting of cells into two new,
  identical cells called daughter cells.

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Why Do Cells Divide?

• DNA overload
• Exchanging Materials
• The volume becomes much larger than the surface
  area

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Chromosomes

• A typical human cell nucleus contains 46
  chromosomes made of DNA.
• You get 23 from mom and 23 from dad.

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DNA

• When DNA is being used for daily activities it
  is called chromatin.
• Chromatin the relaxed fibers of DNA.

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DNA Packing

• When it is time for mitosis, the DNA is copied
  and packed for the move.

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DNA Packing

• To pack, DNA molecules wrap around proteins
  called histones and form a rod-shaped structure
  called a chromosome.

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Chromosome Structure
Section 1 Chromosomes
Chapter 8
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Chromosome Structure

• The copied and packed DNA forms chromosomes.
• The identical halves of a chromosome are called
  chromatids.
• Chromatids are connected by a protein
  bellybutton called a centromere.

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A Chromosome
Chromatid
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Chromosome
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Chromosome Segments

• Chromosomes are divided into segments called
  genes.
• A small segment of DNA that codes for a protein
  that results in a particular trait.
• Alternate forms of a gene are called alleles.

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Chromosome Pairs

• Chromosomes come in pairs.
• Half of the pair came from your mother, the other
  from your father.
• The two chromosomes when together are called
  sister chromosomes or homologous chromosomes.

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A Chromosome
Chromosome from Mother
Chromosome from Father
Sister Chromosomes
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Karyotype
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Cell Cycle

• Life cycle of the cell.
• Made up of the events from one mitosis to
  another.
• Phases are interphase, mitosis, and cytokinesis

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Interphase

• Time for growth and development.
• Cells spend most of their time in interphase.
• The end of interphase is spent preparing for
  mitosis.
• G1 growth 1, doubles in size and gets large
  enough to divide
• S synthesis phase, copies DNA (replication)
• G2 growth 2, copies organelles and makes
  proteins, enzymes that will be needed for mitosis.

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Interphase
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Mitosis

• Follows interphase
• Divides the genetic material (DNA) only.
• Steps involved
• Prophase
• Metaphase
• Anaphase
• Telophase

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Reasons For Mitosis

• Multicellular Organisms
• Growth
• Repair
• Replacement of dead cells/ Maintenance
• Maturation (full grown)
• Unicellular organisms
• Asexual reproduction

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Growth and Maintenance

• Growth an increase in size because of the
  increase in the number of cells.
• Maintenance replacing cells that were dead or
  damaged.

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Prophase

• Chromosomes form
• Nuclear membrane and nucleolus disappear
• Centrioles move to opposite poles
• Spindle fibers begin to form.
• Fibers made by the centrioles that pull the
  chromosome copies apart during mitosis

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Prophase
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Prophase
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Metaphase

• Middle phase
• The chromosomes are pushed and line up on the
  equator or the center of the cell.

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Metaphase
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Metaphase
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Anaphase

• Centromere holding the chromatids together
  splits.
• Spindle fibers shorten and pull the chromatids
  apart.

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Anaphase
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Anaphase
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Telophase

• Chromosomes are at opposite poles.
• Centrioles and spindle fibers disappear.
• The chromosomes begin to uncoil.
• The nuclear membrane and nucleolus reappear.
• Reverse Prophase

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Early/ Late Telophase
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Telophase
Early Telophase
Late Telophase
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Cytokinesis

• Follows mitosis
• Splits the cytoplasm only.
• Results in two identical daughter cells.
• The beginning of the process is indicated by a
  cleavage furrow in an animal cell and a cell
  plate in a plant cell.

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The End !