The Cell Cycle and Mitosis

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The Cell Cycle and Mitosis

• You Complete Me
• A process where one parent cell gives rise to two
  daughter cells- exact replicas of the original
  cell.

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Intro

• Mitosis describes the process by which the
  nucleus of a cell divides to create two new
  nuclei, each containing an identical copy of DNA.
  
• Cytokinesis describes the division of the rest of
  the cell.

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The Cell Cycle

• Every cell goes through a process of growth, this
  is called the cell cycle.
• New cells start at G1 or Gap 1, go on to an S
  phase (where DNA is synthesized in preparation of
  Mitosis), and then G2 or Gap 2 before Mitosis or
  Cell division.

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• Some cells will no longer divide and they exit
  the cell cycle in G1(neurons, muscle cells, fat
  cells do this)
• As one cell enters Mitosis, two cells exit which
  are exact replicas or clones of the original
  parent cell.
• Purpose to replenish dead or dying cells, to
  allow an organism to grow and develop

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Before The Split

• A human cell contains 46 chromosomes.
• Though the genetic code of a human being is
  contained within 46 chromosomes, only half of
  this number exists within the cell of a sperm or
  egg.

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Mitosis

• Mitosis occurs in order for organisms to grow and
  develop. In order to replenish dead or dying
  cells such as skin cells, cells in the digestive
  tract and in the fertilized egg.

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• There are 4 main phases Interphase, Prophase,
  Prometaphase, Metaphase, Anaphase, Telophase.
• Cytokinesis (division of the cytoplasm) follows
  and one cell becomes two.
• We remember by saying
• I perfectly planted my apple tree.

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BERFORE THE BREAK-UP
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Interphase

• This phase encompasses all of the G1,S, and G2
  phases of the cell cycle. The chromatin is
  diffuse.
• It may not look like much is going on here, but
  there is a lot of activity because the cell must
  prepare for Mitosis protein synthesis, DNA
  synthesis, replication of other cellular
  structures too.
• Onion root tip (on left side)

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Interphase

• Interphase is the period between cell divisions.
  During this time, chromosomes replicate -- each
  DNA strand unzips into two strands while
  free-floating bases attach to the unzipped
  strands. The chromosomes are loosely packed and
  not visible with a microscope.
• Two pair of centrioles lie just outside the
  nucleus, next to each other. A centriole is a
  cylindrical structure within the cell that plays
  a part in cell reproduction.

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INTERPHASE
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Mitosis Prophase

• Major processes during this
• phase
• Chromosomes condense and form visible bodies (DNA
  was replicated in S phase)
• Nuclear envelope breaks down
• Onion root tip (top photo)

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Prophase

• Chromosomes begin to condense, normally looks
• like four arms connected at a point. Each
• chromosome is, at this time, actually two
  identical
• copies. Each copy is called a chromatid.
• A spindle begins to form from the centrioles.
  This
• spindle is made of fibers. The centrioles begin
  to
• separate.
• Also, the membrane of the nucleus, or nuclear
• envelope, fragments and disperses.

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PROPHASE
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Prometaphase

• The centrioles are now at opposite ends of the
  cell.
• The spindle fibers from both of the centrioles
  attach to each one of the chromosomes.

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PROMETAPHASE
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Mitosis Metaphase

• Chromosomes attached to spindle fibers line up in
  the middle (the equator) of the cell
• Spindle fibers attach to the centromeres and
  other places along the chromosome
• Onion root tip (top photo)

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METAPHASE
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Mitosis Anaphase

• The last bit of DNA at the centromere replicates
  to allow the the centromere to split
• The sister chromatids separate and are pulled to
  opposite sides of the cell
• Onion root tip (top photo)

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ANAPHASE
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Mitosis Telophase

• Chromosomes now uncoil
• Nuclear envelope reappears and surrounds the
  chromosomes
• The chromatids (now also considered chromosomes)
  arrive at the opposite ends of the cell, and new
  nuclear membranes form. Mitosis, which
  describes only the division of the nucleus, is
  now complete.

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TELOPHASE
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Cytokinesis

• The cytoplasm and all its contents are divided
  between the 2 daughter cells (cytoplasmic
  division)
• The red arrow points at the newly developing
  plasma (cell) membrane that creates the 2 new
  daughter cells
• The 2 daughter cells are exact replicas of the
  original parent cell they are clones and have
  the exact same genetic make-up as the parent
  cell.

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CYTOKINESIS
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Can you identify these stages?
A
B
D
C
Answers A. Telophase B. Prophase C.
Cytokinesis D. Metaphase
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Summary

• One parent cell begins the journey through the
  cell cycle and 2 new identical daughter cells
  emerge from one cycle.
• Mitosis occurs regularly in tissues that require
  new cells continuously such as skin cells, hair
  follicles, the lining of the digestive tract and
  in a newly fertilized egg.
• This process is important as it allows for an
  organism to grow and develop over its lifespan
  and replenishes dead or dying cells in certain
  tissues.

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Homework

• Mutation Quiz Tomorrow!
• Mitosis Wordlist Due tomorrow at the start of
  class
• Mitosis Computer Assignment Due Thursday
• Work on notes from text 533-537
• Textbook Questions p.537 1,2,3,4,5,6

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Exit Activity

• Using the information you have gathered about
  cell
• reproduction and mitosis, complete the following
  brief
• constructed response explaining the following
  scenario.
• If you cut your finger while preparing
  dinner one evening. Explain how mitosis would
  play a role in the healing process.