BIOL 212 Lecture Notes - Lecture 29: Origin Recognition Complex, Cdc6, Spindle Apparatus
18 May 2018
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Lecture 29 Notes
Cell Cycle
- Involves duplication and division of cellular material
o 1: cell growth and chromosome duplication
o 2: chromosome segregation
o 3: cell division
- Completion of cell cycle results in formation of two copies of pre-existing cell
- Times vary over orders of magnitude
- 4 phases:
o Gap1 Phase (grow and duplicate organelles)
o Synthesis Phase (DNA replication)
o Gap2 Phase (cells grow and duplicate organelles)
o Mitosis Phase (mitosis [nuclear division] and cytokinesis [cytoplasmic division])
Cell-Cycle Control System
- Set of regulatory protein, many of which function as biochemical switches controlled by
phosphorylation
- System ensures:
o Proper sequence of steps carried out in the cell cycle
o Each process has been completed before next one begins
- Regulated by feedback from cell cycle processes, in form of checkpoints
- Checkpoints utilize various molecular brakes that can stop the cycle if the previous step is not complete
Oocyte
- Inject cytoplasm from M-Phase Cell into oocyte → spindle easily detected, oocyte is driven into M
phase
- Inject cytoplasm from interphase cell → oocyte does not enter M phase
- Activity called maturation promotion factor (MPF)
MPF Activity and Levels
- MPF (M-Cdk) activity oscillates during cell cycle
- M- cyclin (cyclin B) protein levels oscillate during cell cycle
- MPF activity resides in the M-Cdk complex
M-Cdk
- M-Cdk phosphorylates proteins important for M phase processes
o Chromosome condensation
o Nuclear envelope breakdown
o Mitotic spindle formation
- Kinase activity of Cdk protein is dependent on its binding to cyclin, w/o cyclin Cdk does not work
- M-Cdk activity oscillates cuz of the regulated destruction of M-cyclin
o Cyclin and active Cdk → ubiquitylation of cyclin by APC (anaphase promoting complex) →
destruction of cyclin in proteasome → inactive Cdk
- Proteins are eventually degraded by the proteasome
- M-Cdk activity is also regulate by phosphorylation and dephosphorylation
o Mitotic Cdk → M cyclin and inhibitory kinase (Wee1) → inhibitory phosphate and inactive M-
Cdk → activating phosphatase → active M-Cdk
- M-Cdk reinforces its own activity via a positive feedback loop
o This mechanism helps to explain an abrupt activation of M-Cdk at the start of M phase
- Different cyclin-Cdk complexes trigger different parts of the cell cycle
- Activated cyclin-Cdk complexes phosphorylate different sets of target proteins in the cell
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Document Summary
Involves duplication and division of cellular material: 1: cell growth and chromosome duplication, 2: chromosome segregation, 3: cell division. Completion of cell cycle results in formation of two copies of pre-existing cell. 4 phases: gap1 phase (grow and duplicate organelles, synthesis phase (dna replication, gap2 phase (cells grow and duplicate organelles, mitosis phase (mitosis [nuclear division] and cytokinesis [cytoplasmic division]) Set of regulatory protein, many of which function as biochemical switches controlled by phosphorylation. System ensures: proper sequence of steps carried out in the cell cycle, each process has been completed before next one begins. Regulated by feedback from cell cycle processes, in form of checkpoints. Checkpoints utilize various molecular brakes that can stop the cycle if the previous step is not complete. Inject cytoplasm from m-phase cell into oocyte spindle easily detected, oocyte is driven into m phase. Inject cytoplasm from interphase cell oocyte does not enter m phase. Mpf (m-cdk) activity oscillates during cell cycle.
