BIOLOGY 285 Study Guide - Quiz Guide: Chromosome, Dna Replication, Restriction Point

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16 Nov 2020

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Question 1: explain how cdk activation in g1 leads to commitment to the cell cycle (the. Restriction point aka r in vertebrates aka start in yeast). Be sure to include g1- cyclin/cdk, rb and e2f in your explanation. Once growth factors are received by the cell, the ras/map pathway is activated, and this will produce cyclin-d. cdk4-cyclin d complexes will activate e2f-rb complex through phosphorylation. The phosphorylation of the protein rb will cause it to release the transcription factor e2f and allow it to perform its function. E2f is a family of transcription factors involved in the transcription of proteins required for s phase. Explain. (hint: we"ve discussed them in class, and they are required for dna replication and chromosome segregation) The origin of replication complex it is an atpase on dna that recruits another protein called cdc6 (atpase). This activates the recruitment of cdt1 and mcm-helicase.

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For your responses please justify your answer. No justificationfor answer will recieve "needs work" rating.

32. Which statements concerning the regulation of CDK/cyclincomplexes are correct?
A. At different points in the cell cycle, G1 and mitotic cyclinscan activate the same CDK subunit.
B. Phosphorylation of CDK proteins can both activate and inhibitcyclin/CDK activity.
C. If CAK has phosphorylated the CDK subunit, CDKs will remainactive in the absence of cyclin.
D. The CDK/G1 cyclin complexes that control S phase initiation arelikely to have signal sequences
that target them for nuclear import.
F. Cyclin/CDK complexes are frequently targets of cell cyclecheckpoint pathways.

33. Which of the following statements concerningubiquitin-mediated proteolysis are correct?
A. Ubiquitin modification serves as a molecular âtagâ to signaldegradation by the proteosome.
B. Both G1 and mitotic cyclins are targets for ubiquitin-mediatedproteolysis.
C. Nuclear envelope breakdown during mitosis is accomplished byubiquitin-mediated
proteolysis of lamin intermediate filament proteins.
D. The separation of sister chromatids at the metaphase to anaphasetransition is controlled by
ubiquitin-mediated proteolysis of an anaphase inhibitor.
E. Conditional mutations that inactivate the gene encodingubiquitin in yeast would be expected
to exhibit a cdc phenotype.

The Myc gene is a very important proto-oncogene that encodes the Myc transcription factor. The Myc gene is normally only expressed in response to the presence of growth factors, and once expressed the Myc protein promotes passage through the restriction point by activating the transcription of early cell cycle genes. As an indication of the importance of Myc, overexpression of the Myc protein is sufficient to cause tumorigenesis in many cell types. For example, Burkittâs lymphoma is the result of a chromosomal translocation that leads to increased myc expression in B-lymphocytes.

(A) (3 pts) What is the restriction point, and which CDK complex is most directly activated by passage through the restriction point?

(B) (10 pts) Describe how activation of the CDK complex from part (A) leads to entry of cells into S-phase. Your answer must indicate the protein(s) that this CDK directly acts on, the proteins that directly stimulate S-phase entry, and the mechanism that prevents premature entry into S-phase.

(C) (8 pts) Indicate whether each protein you mention in part (B) is a proto-oncoprotein (e.g. a protein encoded by a proto-oncogene) or a tumor suppressor. You can incorporate this into your answer to part (B) if you choose.

(D) (4 pts) Why does the overexpression of Myc lead to cancer, for example Burkittâs lymphoma?

BIOLOGY 285 Study Guide - Quiz Guide: Chromosome, Dna Replication, Restriction Point

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