Transcript Chapter 21 Regulation of the Eukaryotic Cell Cycle

Chapter 21
Regulation of the Eukaryotic Cell
Cycle
April 6, 2005
Presented by:
Jennifer Payne
Sections within the Chapter
 21.1 Overview of the Cell
Cycle and Its Control
 21.2 Biochemical Studies
with Oocytes, Eggs, and
Early Embryos
 21.3 Genetic Studies with
S. pombe
 21.4 Molecular
Mechanisms for
Regulating Mitotic Events
 21.5 Genetic Studies with
S. cerevisiae
 21.6 Cell-Cycle Control in
Mammalian Cells
 21.7 Checkpoints in CellCycle Regulation
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
activities.
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.
Mitosis
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