Cell Division

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Cell Division

• The way cells reproduce.
•   Cell replacement and body growth are
  mitosis and cytokinesis.
• Sex cell production is meiosis.

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Mitosis

• Nuclear division
•   Cytoplasmic division
•   Division of cell nucleus into 2 genetically
  identical daughter cells
• Before mitosis, the cell undergoes cytoplasmic
  growth and doubles

•  DNA also has duplicated itself. Has double
  set of chromosomes (in humans, now has 92), this
  is called replication.
• This all occurs during the interphase stage
  between mitosis

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Mitosis

• There are 5 stages in mitosis. Look at p. 71 for
  diagrams.

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1. Interphase

• Resting stage
• Chromosomes not visible.
•  Nuclear membrane envelopes nuclear chromatin.

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2. Prophase

• First stage of mitosis.
• Chromosomes thicken into chromatids which are
  connected to each other at centromeres.
• Centrioles (microtubules) migrate to opposite
  poles.
• Spindles are formed from centrioles to
  centromeres.

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3. Metaphase

• Spindle expands.
•  Nuclear membrane completely gone.
•  Chromosomes lined up along center of cell.

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4. Anaphase

• Chromatids are separated and pulled to
  opposite poles.
• Cytokinesis begins with a cleavage furrow through
  cytoplasm.

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5. Telophase

• Chromatids reach opposite poles.
• Now referred to as chromosomes.
• Nuclear membrane forms around chromosomes.
• Spindle disappear.

• Nucleoli form.
• During cytokinesis, cleavage furrow divides
  cytoplasm.
• 2 genetically, identical daughter cells
  are formed.
• Each new cell enters interphase stage.

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Telophase
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Mitosis

• Most body cells are replaced like this. This is
  done to replace dead cells which die by disease,
  wear and tear, and aging.
• Over 1 trillion cells die and need replaced each
  minute. 
• Nerve cells, heart muscle cells, skeletal muscle
  cells are specialized cells not capable of
  dividing. Their functions are taken over by
  neighbor cells or are lost.

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Meiosis

• Sex cell division is meiosis.
• Division of parent cell into genetically
  different daughter cells.
• Each contains 1/2 the number of chromosomes.
• These are the sex cells or gametes which are
  only produced in the sex organs known as gonads.
  Ovaries for females and testes for males.

• Female gamete is ovum and it has 23
  chromosomes.
• Male gamete is sperm and it has 23
  chromosomes.
• Fertilization occurs and you end up with 46
  chromosomes (23 pairs) and this forms a zygote.
• After this occurs, than each sex cell
  undergoes meiosis and the new daughter cells will
  each contain only 23 chromosomes once again.

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Meiosis
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Aging

• Aging is the result of reduction of function
  in cells that lead to their death. There are 3
  ways that aging occurs.
• 1.   cellular senescence
• 2.   free radicals
• 3. autoimmune response

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 1. Cellular Senescence

• Aging is turned on by genetic code.

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2. Free Radicals

• Molecule of oxygen that contains free electrons.
  Capable of damaging proteins. As one increases
  in age, the number of free radicals in the
  cytoplasm increases. Free radicals produced by
  radiation and chemicals.

• Antioxidants inhibit the production of free
  radicals. These include vitamin C, vitamin E
  (vegetable oils, whole grains, leafy green
  vegetables), and selenium.

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3. Autoimmune Response

• When WBC destroy healthy body cells.