BIO 330 Lecture Notes - Lecture 16: Maturation Promoting Factor, Spindle Apparatus, Nuclear Membrane

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24 May 2018
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BIO 330 Lecture notes 16:
Cell Cycle
Cell growth and chromosome replication
Chromosome segregation
Cell Division
M phase
•mitosis, cytokinesis
G1 phase
•protein synthesis, growth, decision about cell division
S phase
•DNA synthesis
G2 phase
•protein synthesis in preparation for mitosis, growth
Early Embryonic Cell Cycle
•Cell divisions in the early embryo follow a modified cell cycle with no G phases and
no expression of embryonic genes, resulting in rapid cell divisions with no overall
embryonic
growth.
Maternal Factors
•(in the yolk) sustain the embryo until the
mid-blastula transition, when G phases begin, cell division rates slow down, and the
embryo begins to grow in size
Cell Division Control System
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•Regulates the events necessary for progression through each phase of the cell cycle.
•Involves specific cell division cycle proteins (Cdc) that are active only during specific
phases
•The control system ensures that events related to progression through the cell
division cycle occur in the proper sequence
•At checkpoints in the cycle, the cell makes sure conditions are right for it to proceed
to next phase (determined by both internal and external signals)
Cyclins
•Regulatory subunits
Cyclin-dependent kinases (Cdk)
•Catalytic subunits
•Only active when bound to cyclin
Active M-Cdk (mitotic Cdk)
•Needed to trigger the events related to mitosis:
-chromatin condensation
-nuclear envelope breakdown
-fragmentation of Golgi apparatus
-formation of the mitotic spindle
•Also know as the maturation promoting factor (MPF)
Chromatin condensation
•Phosphorylation of condensins
Nuclear envelope breakdown
•Phosphorylation of lamins and nuclear pore complexes
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Fragmentation of the Golgi apparatus
•Phosphorylation of Golgi matrix proteins
Formation of the mitotic spindle
•Phosphorylation of centrosome and microtubule-associated proteins
M-Cdk activity
•M-cyclin regulates M-cdk activity
•M-cyclin accumulates to highest level during M-phase
•M-cyclin is destroyed at the end of M-phase
•M-Cdk activity depends on M-cyclin concentration
Inactivation of M-cyclin/M-Cdk complex
•At the end of mitosis, the M-cyclin/M-Cdk complex is inactivated by the selective
degradation of M-cyclin
•The destruction of M-cyclin occurs near the end of M-phase and follows the
ubiquitin pathway
•Activated anaphase promoting complex (APC) adds ubiquitin to cyclin and to other
proteins involved in the regulation of mitosis
•APC is activated (via phosphorylation) by M-Cdk
Discovery of an active MPF during M-phase
•A G2-arrested oocyte can be driven to enter M-phase by injecting cytoplasm from an
M-phase donor cell
•A G2-arrested oocyte injected with cytoplasm from an interphase donor cell, will not
enter M-phase
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