Biol110-08-Prob Key 8

Biol110-08-Prob Key 8 - Biol110 Cell Biology Problem Set...

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Biol110 Cell Biology Problem Set #8-Key Michael F. Rexach, Associate Professor, MCD Biology E-mail: [email protected] Question #1 Cell cycle stages What do G1 and G2 stand for? What is monitored during these stages of the cell cycle? They stand for gap #1 and gap #2; these are periods of time when the cell monitors: in G1 external signals such as nutrient availability, signals to proliferate or not, cell size, etc; and in G2 internal signals such as are the centrioles duplicated, has the DNA been duplicated, etc. How is G1 extended in time to last anywhere from hours to weeks? It is extended by several mechanisms that act on cyclins or cyclin-CDK complexes. First, the synthesis of cyclin is lowered at the gene expression level. Second, cyclin can be targeted for degradation via the proteasome pathway; and third, a cyclin- CDK inhibitor (CKI; p27; sic1) can cover the active site of CDK. What steps in the cell cycle are vectorial? In other words, which molecular events are not reversible and when are they executed? The most vectorial steps in the cell cycle are those that involve proteolysis, as it is terminal. Cyclin proteolysis at various stages of the cell cycle drives the transition between each stage to the next (M>G1; G1>S; S>G2: G2>M). What is the precise molecular role of the APC and SFC ligases? What is the
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This note was uploaded on 06/23/2008 for the course BIO 110 taught by Professor Rexach during the Spring '08 term at UCSC.

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Biol110-08-Prob Key 8 - Biol110 Cell Biology Problem Set...

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