Regulation of the Eukaryotic Cell Cycle (PowerPoint)

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					          Chapter 21
Regulation of the Eukaryotic Cell
            April 6, 2005

             Presented by:
            Jennifer Payne
     Sections within the Chapter
 21.1 Overview of the Cell    21.5 Genetic Studies with
  Cycle and Its Control         S. cerevisiae
 21.2 Biochemical Studies     21.6 Cell-Cycle Control in
  with Oocytes, Eggs, and       Mammalian Cells
  Early Embryos                21.7 Checkpoints in Cell-
 21.3 Genetic Studies with     Cycle Regulation
  S. pombe
 21.4 Molecular
  Mechanisms for
  Regulating Mitotic Events
21.1 Overview of the Cell Cycle
        and Its Control
 There are ordered series of events that eukaryotic cells
  proceed through, which constitutes the cell cycle.
 During the cell cycle the cells chromosomes are
  duplicated and one copy of each of the chromosomes
  segregates into two daughter cells.
 The regulation of the cell cycle is essential for normal cell
  development of multicellular organisms. Any loss of
  control can result in cancer, a disease that leads to death
  in one in every six people.
            Overview continued
 Cell replication is primarily controlled by regulating the
  timing of two critical events in the cell cycle: nuclear DNA
  replication and mitosis.
 The main controllers of these events are heterodimeric
  protein kinases that contain a regulatory subunit and a
  catalytic subunit.
 The kinases regulate the activities of multiple proteins
  involved in DNA replication and mitosis by
  phosphorylating them at specific regulatory sites,
  activating some and inhibiting others to coordinate their
  The Ordered Series of Events
 Leading to Replication of Cells
 The cell cycle is divided
  into four major phases: 1. S
  phase 2. G2 phase 3. M
  phase 4. G1 phase
 Each of these phases have
  their own series of events
  until the cell is duplicated
  into two daughter cells at
  the end of the M phase.
 The M phase is when the
  process of mitosis occurs.
  Four Phases of the Cell Cycle
 In the S (synthesis phase) the chromosomes
  are replicated.
 After the cell progresses through the G2
  phase the cell then begins mitosis.
 Mitosis occurs during the M phase of the
  cell cycle. Mitosis is divided into several
  different stages.
           Following Mitosis
 The G1 phase follows mitosis. This phase is
  the period before DNA synthesis is
  reinitiated into the S phase.
 In vertebrates and diploid yeasts the cells in
  G1 have a diploid number of chromosomes
  (2n), one inherited from each parent.
 In haploid yeasts, cells in G1 have one of
  each chromosome (1n).
      Length of the Cell Cycle
 There are rapidly replicating human cells
  that progress through the entire cell cycle in
  approximately 24 hours.
 Mitosis takes around 30 minutes; G1, 9
  hours; S phase, 10 hours; and G2, 4.5 hours.
 In growing yeast cells the cycle only takes
  about 90 minutes combined.
                  Postmitotic Cells
 The postmitotic cells can leave
  the cell cycle and remain for
  days, weeks, or sometimes the
  lifetime of the organism.
 Cells that remain the lifetime of
  the organism does not
  proliferate any further.
 In vertebrates cells leave the
  cell cycle in G1 phase and enter
  into a phase called G0.
 G0 cells returning to the cell
  cycle enter into the S phase.
A Pictorial Representation of the Cell Cycle

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