GRE Subject Test: Biology : Understanding Cycle Regulation

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #113 : Cell Biology

How does the cell progress through various stages of the cell cycle?

Possible Answers:

Each cell type has a natural time frame for each portion of the cell cycle that is independent of protein expression

Controlled expression and degradation of various cyclin proteins

Controlled expression and degradation of various cyclin-dependent kinase (CDK) proteins

Controlled expression and degradation of both cyclin and cyclin-dependent kinase (CDK) proteins

Correct answer:

Controlled expression and degradation of various cyclin proteins

Explanation:

Cells progress through the cell cycle by controlled expression and degradation of cyclin proteins. Cyclin-dependent kinases (CDKs) are always present in the cell and are not degraded after progression to a new stage of the cell cycle. Cyclins bind their respective CDKs to activate them. This activation causes a chain of events that allow the cell to progress to the next phase of the cell cycle. Afterwards, cyclins are ubiquinated and degraded until they are needed again.

Example Question #114 : Cell Biology

Cytokinesis begins during which phase of mitosis?

Possible Answers:

Anaphase

Telophase

Prophase

Prometaphase

Metaphase

Correct answer:

Anaphase

Explanation:

During anaphase, sister chromatids are pulled apart towards opposite poles. The cell becomes longer and the cleavage furrow (contractile ring) forms. This marks the beginning of cytokinesis. The process completes during telophase, producing two new daughter cells. Cytokinesis must be preceeded by karyokinesis (physical movement of the chromosomes).

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