Cell Cycle Regulation - Genetics
1. What are the different restriction points of the cell cycle? Describe each.
G1 (Restriction) Checkpoint * End of G1, just before onset of the S phase (DNA replication) * Yeast “start”; other eukaryotes “restriction point” * The options for the cell at this point: * divide, delay division, or exit the cell cycle * Cells can exit the cell cycle at this point into an arrested stage (G0) * When this checkpoint is passed, cdk4 and cyclin D interact. This interaction results in phosphorylation of the retinoblastoma protein, which in turn allows activation of the transcription factor E2F. Active E2F promotes expression of the cyclin E gene. Cyclin E (protein) and cdk 2 interact to promote the G1 to S phase transition.
DNA Replication Checkpoint (end of G2) * Cell will not proceed with mitosis if DNA replication is not complete * The way the cell senses this is not understood completely * This checkpoint involves signals that block the activation of
M phase cyclin-cdk complex (MPF) by inhibiting the activity of cdc25 protein phosphatase. * Cells with mutations in this checkpoint pathway or cultured mammalian cells treated with caffeine will proceed through mitosis with unreplicated DNA.
Spindle-attachment checkpoint * Before anaphase (separation of chromosomes) there is a checkpoint to ensure the chromatids are correctly attached to the mitotic spindle * The kinetochore (where the chromatids attach to the spindle) is the structure that is monitored * Unattached kinetochores negatively regulate the activity of cdc20-anaphase promoting complex (APC), and anaphase is delayed
Mitosis
* Degradation of the M phase cyclin/cdk complex (aka MPF) is required to proceed with the final activities of mitosis (spindle disassembly and formation of the nuclear envelopes). * This degradation is accomplished by ubiquitinylation of the
G1 (Restriction) Checkpoint * End of G1, just before onset of the S phase (DNA replication) * Yeast “start”; other eukaryotes “restriction point” * The options for the cell at this point: * divide, delay division, or exit the cell cycle * Cells can exit the cell cycle at this point into an arrested stage (G0) * When this checkpoint is passed, cdk4 and cyclin D interact. This interaction results in phosphorylation of the retinoblastoma protein, which in turn allows activation of the transcription factor E2F. Active E2F promotes expression of the cyclin E gene. Cyclin E (protein) and cdk 2 interact to promote the G1 to S phase transition.
DNA Replication Checkpoint (end of G2) * Cell will not proceed with mitosis if DNA replication is not complete * The way the cell senses this is not understood completely * This checkpoint involves signals that block the activation of
M phase cyclin-cdk complex (MPF) by inhibiting the activity of cdc25 protein phosphatase. * Cells with mutations in this checkpoint pathway or cultured mammalian cells treated with caffeine will proceed through mitosis with unreplicated DNA.
Spindle-attachment checkpoint * Before anaphase (separation of chromosomes) there is a checkpoint to ensure the chromatids are correctly attached to the mitotic spindle * The kinetochore (where the chromatids attach to the spindle) is the structure that is monitored * Unattached kinetochores negatively regulate the activity of cdc20-anaphase promoting complex (APC), and anaphase is delayed
Mitosis
* Degradation of the M phase cyclin/cdk complex (aka MPF) is required to proceed with the final activities of mitosis (spindle disassembly and formation of the nuclear envelopes). * This degradation is accomplished by ubiquitinylation of the
References: http://www-personal.umich.edu/~cooper/checkpoint.pdf http://www.landesbioscience.com/journals/cc/article/108/?nocache=355652282 http://www.ncbi.nlm.nih.gov/books/NBK6318/ http://labs.fhcrc.org/fero/CCdescription.html http://www.nature.com/scitable/topicpage/cell-cycle-control-by-oncogenes-and-tumor-14191459 http://www.news-medical.net/health/What-are-Oncogenes.aspx http://biochemistry.ucsf.edu/programs/ptf/m3%20links/TumorSuppressLEC.pdf http://www.youtube.com/watch?v=A7bA8b3-Dhg (Video) http://www.sparknotes.com/biology/cellreproduction/cellcycle/section3.rhtml http://biop.ox.ac.uk/www/lj2001/endicott/endicott.html