BIOLOGY 2B03 Lecture 10: (Module 10) Checkpoints That Maintain Cell Integrity
30 Nov 2016
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Bio2b03- module 10: checkpoints that maintain cell integrity. Cells exit the cell cycle & enter g0. In mammals, most cells have entered g0 & will never re-enter cell cycle; they instead have differentiated & will undergo apoptosis. Replacement of lost cells depends upon cell division of associated adult stem cells, followed by cell differentiation. E. g. (of post-mitotic cells) red blood cells; nerve cells; muscle cells. Some cells withdraw temporarily & re-enter g1 when they receive a certain signal. Recall: cell cycle of fission yeast requires single cyclin & single cdk for regulation. Vertebrates- multiple cyclin & cdk variants that control transitions between cell cycle phases. D-type cyclins & cdk4/cdk6 regulate events in early g1 phase; Cyclin e-cdk2 triggers s phase; cyclin a-cdk2 & cyclin a-cdk1 regulates completion of s phase; cdk1-cyclin b responsible for mitosis. Re-entry into cell cycle requires expression of d-type cyclins & cdk4/6. Mitogens/growth factors: signaling molecules that induce cell division by causing expression of g1 cyclin/cdk.
