Stages of Mitosis

Prophase-chromsomes condense, mitotic spindle forms.

Prometaphase-nuclear envelope breakdown,

  spindle attaches to kinectochores

Metaphase- chromosomes align midway between spindle poles

Anaphase-sister chromatids separate into daughter chromosomes.

Telophase- chromosomes reach poles, nuclear envelope reforms.

Cytokinesis-cytoplasm is divided to create two daughter cells.

MPF

mitotic cyclin/CDK

-MPF stimulates entrance into mitosis.

-High levels of MPF freeze the cell at metaphase.

-Degradation of MPF allows cells to finish mitosis.

Thus,  completing mitosis requires something else.

Something else is…

            Anaphase Promoting Complex (APC).

Anaphase Promoting Complex

-Anaphase Promoting Complex (APC) is required to exit metaphase and to enter anaphase, i.e., promote anaphase.

-APC is active at the time points that MPF begins to fall.

-APC is a ubiquitin ligase that targets cyclin B.

After all, the cell has to reform nucleus and cellular structures that dissolve during mitosis.  Cyclin B/CDK activity induce this dissolution.

Mitotic Cyclin Summary

5.  APC is activated by MPF phosphorylation.  

Checkpoint Controls

1.  Complete Synthesis of DNA

  -ensures daughter cells get complete genome.

 2.  Cell Growth and Nutrients.

  -ensures sufficient energy and cell material to make 2 cells

  3.  DNA Damage-Radiation or Chemical toxins.

  -double stranded breaks could result in loss of chromosome

  4.  Mitotic Spindle.

  -chromosome loss due to unequal distribution of chromosomes

Multiple Levels of Regulation

Multiple Levels of Regulation

-Cyclin Expression*

  -Cyclin Degradation*

  -Phosphorylation of CDK*