Cell Cycle

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					• http://www.youtube.com/watch?v=wRrNjH
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The Cell Cycle
              INTERPHASE
• 90% of a cell’s life
  cycle
• Comprised of three
  subphases
  – G1
  –S
  – G2
                      G1
• Primary Activity is
  Protein Synthesis and
  Cell Growth.
• At end of G1, cells
  reach a
  RESTRICTION
  POINT (“Go or No Go”)
• Cells Either Enter G0
  or go on to S phase
G0
 • If cells do not pass
   the restriction point at
   the end of G1, they
   enter G0
 • Cells in G0 will never
   divide again
 • Most somatic (body)
   cells are in G0
       Finger Regeneration:
http://www.youtube.com/watch?
         v=ITxx2sOLW2Y
                  S Phase
• Cells that DO pass
  the restriction point
  enter the S phase
• In S phase, DNA is
  replicated
• Control over S phase
  regulated by the
  enzyme kinase
G2
 • At the end of S
   phase, cells re-enter
   a period of protein
   synthesis and
   organelle
   development
           M Phase = Mitosis
• NOTE: NOT A PART
  OF INTERPHASE
• If cells pass the
  restriction point, they
  must undergo S, G2
  and finally, the
  division of the genetic
  material known as
  MITOSIS
The length of the cell cycle varies
         on the species
 Length of cell cycle also depends on
the cell function WITHIN an organism
WHY DO CELLS EVER HAVE TO DIVIDE?
                 Surface Area To Volume




• As the cell increases in size, the volume (cytoplasm) of
  the cell grows faster than the surface area

• With more cell volume to feed, cell is required to do more
  diffusion, but can’t speed up RATE of diffusion

• Cell also cannot excrete wastes via diffusion effectively
MAJOR LIFE EVENTS
Do individual cells have a life history?
             Mitosis (M Phase)
• To ensure a high surface
  area to volume ratio (and
  to reduce the need for
  more DNA), the cell
  undergoes mitotic division
• Mitosis is comprised of
  four subphases;
  prophase, metaphase
  anaphase and
  telophase
               Early Prophase
• chromatin begins to coil
  and condense to form
  chromosomes
• each chromosome
  appears to have two
  strands (each containing
  a single DNA molecule)
• each strand is called a
  chromatid
• each chromatid is
  attached to its sister
  chromatid at the
  centromere
              Late Prophase
• the nuclear envelope
  and nucleolus
  disappear
• in cytoplasm, the
  spindle apparatus
  forms
• eventually the spindle
  guides the separation
  of sister chromatids
  into the two daughter
  cells
METAPHASE
    • spindle grows and forms
      attachments to the
      chromosomes at the
      centromeres
    • chromosomes move to an
      equatorial plate which is
      formed along the midline
      between the poles
    • chromosomes are at their
      most condensed state
                   ANAPHASE
• centromeres divide to
  create two chromosomes
  instead of a pair of attached
  chromatids
• spindle fibers shorten and
  the sister chromosomes are
  drawn to the opposite poles
  of the cell
• poles of the spindle
  apparatus are pushed apart
  as the cell elongates
• anaphase results in the
  exact division of genetic
  information to each
  daughter cell
TELOPHASE
    • nuclear envelopes
      reassemble and surround
      each set of daughter
      chromosomes
    • nucleoli reappear inside
      the newly formed nuclei
    • chromosomes
      recondense in the
      daughter cells to become
      chromatin
               CYTOKINESIS
• in animal cell, a
  furrow appears
  around the cell that
  eventually pinches
  the cell into two new
  cells
• in plants, a cell plate
  forms between the
  two daughter nuclei
  as the cell wall
  divides the cell
         Variances In Mitosis
• At any given time,
  different parts of an
  organism may be in
  different parts of the
  cell cycle
• Different organs,
  tissues and structures
  in the body also
  perform mitosis at
  different rates
Lab: Comparitive Cell Cycles In
        Allium cepa
Comparative Cell Cycles in Allium cepa

• Purpose: To compare the relative
  proportion of time required to complete the
  cell cycle in two different regions of an
  organism’s anatomy
• Two zones of root growth in Allium cepa
  – Zone of elongation
  – Zone of maturation
How do the lengths of the various parts of the
  cell cycle (including mitotic subphases)
    compare? Why are they different?
                    Protocol
• For each lab pair, one lab partner will assess the
  zone of elongation, one will assess the zone of
  maturation
• While the other partner tallies the results, the
  other partner should view the required region of
  the slide and classify each of the cells in the field
  of view based on its place in the cell cycle
• Continue until 100 cells have been assessed
• Move the slide to the zone of maturation and
  switch roles with your partner. Repeat
                      Analysis
• Based on your collected results, construct two pie charts
  for the percentage of time spent in each of the cell cycle
  phases (interphase, prophase, metaphase, anaphase
  and telophase).

• In a paragraph, contrast the reasons behind the
  differences. Use the following terms: G1, G2, S, G0, zone
  of elongation, zone of maturation, mitosis, anaphase,
  telophase, metaphase, prophase, cytokinesis,

• Explain the differences regarding the function of each
  subphase and the actions in each of the subphases

				
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posted:12/19/2011
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