Cell Cycle Regulation - Genetics

1387 Words6 Pages
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
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Therefore, mutations in tumor suppressor genes are recessive at the level of an individual cell. As we will see, the inactivation of tumor suppressor genes plays a major role in cancer.

3. In a tabulated form, present the different proteins and genes involved in the regulation of the cell cycle. Include their functions and their classifications as oncogene and tumor-suppressor gene. Protein/Gene | Function | Classification | Retinoblastoma (RB) protein | * located on chromosome 17p13.1, is the single most common target for genetic alteration in human tumors * tumor suppression protein that is dysfunctional in many types of cancer. One highly studied function of pRb is to prevent excessive cell growth by inhibiting cell cycle progression until a cell is ready to divide. It is also a recruiter of several chromatin remodelling enzymes such as methylases and acetylases. | Tumor Suppressor Gene | Cdk inhibitors | * drives the cell cycle by unregulated activation of cyclins and CDKs | Tumor Suppressor Gene | P16 | * is a common target of deletion or mutational inactivation in human tumors * an inhibitor of Cdk4-cyclin D complexes; * The loss of p16 leads to increased Cdk4-cyclin D activity | Tumor Suppressor Gene | P53 | * located on chromosome 17p13.1, is the single most common target for genetic alteration in human tumors | Tumor Suppressor Gene | BRCA1 and BRCA2 | * located on
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