Cell Division

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Cell Division

• Part One Mitosis

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In this lesson

• Explain the difference between double and single
  stranded chromosome, chromatin and chromatid
• List the steps of mitosis and describe what
  happens in each
• Identify what stage of mitosis a cell is in by
  looking at the chromosomes
• List three reasons cells divide by mitosis
• Describe cytokinesis

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In the nucleus

• In non-dividing cells, the genetic material is
  stored as thin DNA super coils called CHROMATIN
• When a cell divides, the chromatin will shorten
  and thicken into CHROMOSOMES
• One strand of a double stranded chromosome is
  called a CHROMATID

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Mitosis

• MITOSIS a process by which the nucleus of a cell
  divides while maintaining the chromosome number
• One cell ? two cells
• New cells have identical genetic material (DNA)
  of the parent cell
• Four stages of division (Prophase, Metaphase,
  Anaphase and Telophase - PMAT) plus a period of
  growth and metabolism called Interphase

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The Cell Cycle
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Interphase

• Period between divisions
• Longest part of the cell cycle
• Cell is growing and metabolizing
• Nuclear membrane present
• Genetic information in the form of chromatin and
  cannot be seen with a microscope
• Before division each strand of DNA will replicate
  (copy) itself to become double stranded
• Near the end of interphase the DNA begins to
  condense (shorten)

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Interphase
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Draw a double stranded chromosome. Label
chromosome, chromatid and centromere
Chromatid
Chromosome
Chromatid
Centromere
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Phase One Prophase

• Chromatin contracts and becomes visible
  (spaghetti). It is now called CHROMOSOMES
• Each is a double chromosome with a pair of SISTER
  chromatids which are joined to each other by a
  centromere
• Chromosomes begin to move towards the equator
  (center) of the cell
• Nuclear membrane disintegrates (breaks down)
• CENTRIOLES will form SPINDLE FIBERS that will
  attach to each centromere and move around the
  chromosomes

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Prophase
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Phase Two Metaphase

• The centromeres of each chromosome line up along
  equator ( looks like praying hands)
• Centromeres divide so the doubled chromosomes
  become two identical single stranded sister
  chromatids
• Centrioles are now at the poles of the cell and
  are attached to each centromere by spindle fibers

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Metaphase
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Phase Three Anaphase

• The spindle fibers begin to shorten and the
  chromosomes begin moving to opposite ends or
  poles of the cell (fingers)
• Each side gets one chromatid from each double
  stranded chromosome

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Anaphase
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Phase Four Telophase

• Begins when single stranded chromosomes reach the
  poles
• Chromosomes uncoil and turn into chromatin
• Nuclear membrane reappears
• Reverse of prophase
• Division of the cytoplasm or CYTOKINESIS is
  completed by pinching off in animals or by
  building a cell wall in plants

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Telophase
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Whats the point of Mitosis?

• Mitosis creates identical copies of cells for
• 1. growth
• 2. Repair/regeneration of damaged tissue
• 3. Asexual reproduction (animals) or
  vegetative reproduction (plants)

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Asexual Reproduction

• Reproduction that involves only one parent
  parent and offspring have identical genetics
• No special reproductive cells or organs used to
  create offspring
• Occurs through mitosis and cytokinesis
• Both single and multi-celled organisms, plants
  and simple animals can reproduce asexually
• In multi-cellular organisms, the offspring
  develop from undifferentiated, unspecialized
  cells from the parent
• Usually a rapid form of reproduction

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Binary Fission

• Simplest form of asexual reproduction
• Parent divides into two approximately equal sized
  daughter cells
• Bacteria circular chromosome attaches to plasma
  membrane then replicates, cell wall separates
  each copy
• Protozoa eg. Amoeba become circular and use
  mitosis

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Budding

• New individuals develop from small outgrowths of
  the parent (buds)
• May develop colonies (sponges) or break off to be
  individuals (hydra, yeast)
• Some organisms can both bud and reproduce
  sexually

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Spores

• Specialized single cells that are released from
  the parent organism, germinate and grow by
  mitosis
• New cells differentiate to form a new organism
• Can reproduce quickly and in large quantities
• Often have thick protective coats
• Eg. Fungi, algae, protozoa

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Regeneration

• The ability to regrow lost body parts
• Some animals can regrow entire new organisms from
  parts
• Ability to regenerate decreases as organisms
  increase complexity
• Even simple organisms that can regenerate entire
  organisms generally prefer to utilize a different
  method to reproduce

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Vegetative reproduction

• MERISTEM area on plant with unspecialized cells
  (cells that can become any kind of cell) that
  frequently divide using mitosis
• Meristematic cells can be found in the vegetative
  structures of a plant (roots, stems, leaves)
• Given proper treatment, meristem cells can
  reproduce mitoticlly then differentiate into new
  independent plants
• Structures include bulbs, corms, tubers, runners,
  rhizomes
• Can also be artificially propagated using
  cuttings, layerings or grafting

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Bulb

• short underground stem with thickened storage
  leaves
• small new bulbs sprout from the old ones
• Eg. onions, tulips

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Corm

• short underground stems with no fleshy leaves
• Eg. gladiolas, crocuses

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Tuber

• enlarged part of an underground stem that
  contains stored food
• potatoes (eyes are tiny buds)

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Runner

• AKA stolon
• is a stem that runs sideways and contains buds
• Eg. strawberry

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Rhizome

• a stem that grows sideways under the ground
• ferns, irises

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Cutting

• a stem, root or leaf cutting used to make a new
  plant

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Layering

• part of a stem is bent and covered in soil
• once it roots the original can be cut off
• Eg. raspberries, roses

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Grafting

• stem or bud removed from one plant and
  permanently joined to another plant
• Eg. grapes and many seedless fruits