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Cell Cycle Unit I biochemistry


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What are the stages of the cell cycle?
Mitosis and interphase
Interphase contains (G1, S, and G2 phases)
What occurs during the S phase?
Replication of nuclear DNA (i.e.) chromosomes
Cells contain athe diploid number (2n) amount of DNA before S phase; after S, the amount of DNA is doubled (4n) in preparation for cell division
Duplicated chromosomes consist of two identical chromatids called ___________
Sister chromatids
What occurs during the G2 Phase?
Metabolism of RNA, regulatory proteins and enzymes necessary for mitosis to take place
DNA is analyzed for possible errors and errors are corrected before mitosis
During this period, the cell has two complete diploid sets of chromosomes
What occurs during the G1 Phase?
Cell volume is restored to normal 2n DNA
Metabolism of RNA, regulatory proteins, and enzymes necessary for DNA replication
Cells can withdraw from the cell cycle into G0 (outside) during G1 and stop dividing for long periods of time or indefinitely.
3 types of experimental systems for cell cycle research
Biochemical analysis of animal eggs and embryos
Identification of yeast cell division cycle mutants
Mammalian cell fusion experiments
MPF (Mitosis Promoting Factor) is required for: (4)
Chromatin condensation
Nuclear envelope breakdown
Fragmentation of ER and Golgi apparatus
Reorganization of microtubules to form the mitotic spindle
What parallels MPF activity?
Cyclin B Levels
What happens when cells are treated with cyclohexamide?
Protein synthesis is required for MPF and cyclin B, treatment blocks cyclin B synthesis, chromosome condensation and nuclear envelope breakdown.
MPF is a complex consisting of:
cyclin B and a cyclin dependent kinase (M-Cdk)
What effects do Cdc25 and Wee1 have on MPF?
Cdc25 and Wee1 have opposing effects on MPF. Wee1 inhibits MPF while Cdc25 stimulates activity.
Name the 3 checkpoints in the cell cycle, where they are and what they check for.
G1 to S phase transition (Is the environment favorable?)
G2 to M phase transition (Is all DNA replicated?, Is environment favorable?)
Metaphase checkpoint (Are all chromosomes attached to the spindle?)
Cyclin dependent Kinases (Cdks) What do they do?
Activity rises and falls through the cycle and lead to cyclic changes in the phosphorylation of intracellular proteins that initiate or regulate the major events of the cell cycle.
Cyclins: What do they do?
Bind to Cdks to cyclically regulate their activity. Cdks are dependent on cyclins for their activity. Cyclin levels undergo a cycle of synthesis and degradation with each cell cycle.
Four classes of cyclns and what they do.
G1/S cyclins bind to CdKs at the end of G1 and commit the cell to DNA replication
S-cyclins bind Cdks during S phase and are required for the initiation of DNA replication.
M-cyclins prompote the events of mitosis
G1 cyclins help promote the passage through start or the restriction point in late G1
Two ways in which the Cell cycle is controlled with cyclins
Proeteolysis of cyclins- cyclins are destroyed by a ubiquitin dependent mechanism that marks the protein for destruction
Transcription- Cyclin levels controlled by changes in cyclin gene transcription and cyclin synthesis
What does SCF do?
Ubiquitynates G1/S cyclins and certain CKI proteins that control S-phase initiation. SCF activity is regulated by the phosphorylation status of target proteins.
What does Anaphase promoting complex (APC) do?
Ubiquitynates M cyclins and other regulators of mitosis. APC activity is regulated at different stages in the cell cycle via the addition of specific subunits.

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