The Cell Cycle 2
Terms
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- Regulator of cell cycle in eukaryotic cells
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Protein Kinases
-Which are controlled by growth factors - Events during Mitosis
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1 hour
Seperation of daughter cells
Cell division (cytokinesis) - Events during Interphase
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G1, S, G2
Chromosomes decondense
Nucleus appears uniform - G0
- Phase in which cell continues to do normal physiological function but does not divide
- Early Embyonic Cells
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Cell cycle lasts 30 min or less
NO cell growth
NO G1 and G2 phases
DNA replication is very rapid - Regulation of Cell Cycle
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External signals-->growth factors
Internal signals-->cell growth, DNA replication, mitosis - G1
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START point is present
Once initiated, there is no turning back - G2
- Stimulated by extracellular signals like hormones.
- G1 Phase Checkpoint
- DNA is repaired before entering the S phase
- S Phase Checkpoint
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DNA damage is repaired before it is replicated
DNA misincorporation is repaired before it is replicated - G2 Checkpoint
- Prevents mitosis if DNA replication is not complete or DNA is damaged
- M Phase Checkpoint
- Prevents mitosis if the daughter chromosomes are not aligned.
- Mechanism of cell cycle arrest
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-Sensor protein detect DNA damage
-Senor proteins activate ATM and ATP
-Phosphorylation of Chk 1 & 2 & ATM increase levels of p53 which leads to cell cycle arrest - Role of MPF
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Maturation Promoting Factor
Required to transition from G2 to M phase - Cyclin B
- A regulatory subunit required for Cdc2 protein kinase activity
- P-Thr-161
- Required for Cdc2 kinase activity
- P-Try-15 & P-Thr-14
- Inhibit Cdc2 kinase activity
- Activation of MPF is dependent on?
- Dephosphorylation of Try-15 and Thr-14
- Triggers the degradation of Cyclin B
- Activation of Cdc2
- Activates transcription of p21
- Increase in level of p53
- Mechanism of p21
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1) Inhibits Cdk/cyclin complexes by binding to them leading to cell cycle arrest
2) Bind to PCNA to inhibit DNA replication - Events in Mitosis
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1) Chromosome condensation
2) Formation of mitotic spindle
3) Attachment of chromosomes to spindle
4) Seperation of sister chromatids
5) Formation of daugher nuclei - 4 Stages in Mitosis
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Prophase
Metaphase
Anaphase
Telophase - Prophase
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Beginning-Appearance of condensed chromosomes
End-Breakage of nuclear envelope in higher eukaryotes - Metaphase
- Chromosomes align in the center of mitotic spindle
- Anaphase
- Breakage of the link between the sister chromatids
- Telophase
- Nuclei reform and chromosomes decondense, cell begins to break apart
- Processes which are promoted by activated MPF
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Chromatin condensation
Nuclear envelope breakdown
Fragmentation of Golgi and ER
Spindle Formation - Cytokinesis
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Completion step of mitosis
Intiated in late anaphase
Triggered by inactivation of MPF
Contraction of actin-myosin filaments - Result of mitosis
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Diploid daughter cells
Identical genetic components - Result of meiosis
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Haploid daughter cells
Half the number of chromosomes - Fertilization
- Sperm binds to receptor on surface of egg and fuses with egg plasma membrane-->produces a new diploid cell
- Effect of sperm binding to egg on Ca2+ levels
- Cytoplasmic Ca2+ levels increase via hydrolysis of PIP2
- Effect of increased Ca2+ levels
- Exocytosis of secretory vesicles leads to surface alterations and blocks entry of additional sperm