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