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17 Cards in this Set

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What are the three stages of interphase?
1) S phase - middle of interphase when DNA is copied and the unpaired chrosomes are replicated
2) G1 - follows mitosis, when cell makes decision to continue growing to enter a resting state termed Gzero.
3) G2 - follows S. Chrosome condensation, nuclear evelope breakdown and mitotic spindle formation are initiated if DNA replication sucessful.
What are the requirements to pass the restriction point, or R?
1) cell must not be programmed to enter Gzero.
2) must be sufficient nutrients for cells to grow large enough so that daughter cells will be of appropriate size
3) cells must have permissive environment with appropriate contact with neighboring cell and EM
4) must be exposed to appropriate growth factors in early G1
Why do cells enter Gzero?
One reason is that they go on to differentiate, eg.: skeletal muscle, neurons
What the general cell cycle generation time?
16 hours
What allows determination of the lengths of time for G1, S and G2 and how does it work?
Thymidine labeling. A culture is briefly exposed to labeled thymidine which is then incorporated into the DNA, then the time it take for the appearance of labeled mitotic cells is measured.
If one took a "donor" cell in early mitosis and fused it another "host" cell in either G1 or S, then...
Nucleus of host cell was stimulated to undergo mitosis immediately.
What is the diffusible factor that triggers mitosis?
MPF, mitosis promoting factor.
What are the two subunits of MPF?
1) serine-threonine kinase called cell division kinase 1, or *CDK1*
2) a regulatory subunit called cyclin B
What activates CDK1 kinase?
cyclin B and certification that DNA synthesis is complete (i.e. kinases and phosphatases that adjust its phosphorylation state)
What deactivates CDK1 kinase?
destruction of cyclin B by proteasomes, at which point mitsosis is allowed to go through anaphase and telophase to completion.
What are the 3 functions of MPF (CDK1 kinase/cyclin B)?
1) Phosphorylation of nuclear lamins and nuclear envelope breakdown
2) Phosphorylation of condensin and chromosome condensation
3) Reorganization of microtubules and spindle formation
Describe each function in detail.
Look at p. 62 of Warren notes
Why do checkpoints in mitosis exist?
Prevents the extremely serious soncequences of improper replication and distribution of genetic material to daughter cells. Without checkpoints, cancer can arise.
What are 2 checkpoints in mitosis?
1) Blockage of mitosis until completion of DNA synthesis
2) The Spindle Assembly checkpoint (makes sure all chrosomes properly aligned at metaphase plate)
What is aneuploidy?
Unequal numbers of chromosomes.
What are two roles of APC related to the spindle assembly checkpoint?
Once metaphase plate is organized, APC (tumor suppressor protein) is activated by CDK1-cyclin B complex. APc 1) initiates destruction of anaphase inhibitor protein. After chromatids are separated and anaphase begins, 2) APC triggers desctruction of cyclin B.
To what stage does CDK1-cyclin B push mitosis by itself?