GRE Subject Test: Biology : The Cell Cycle

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

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Example Questions

Example Question #1 : The Cell Cycle

Which part of the cell life cycle is not part of interphase?

Possible Answers:

M phase

G1 phase

G2 phase

S phase

Correct answer:

M phase

Explanation:

Interphase is the portion of the cell life cycle where the cell is preparing for division. This portion of the life cycle includes growth, as well as reproducing organelles and proteins. The genome is also replicated in interphase. Interphase is composed of the G1, S, and G2 phases. G1 and G2 correspond to periods of growth, protein synthesis, and organelle replication. The S phase is the period of DNA replication.

The M phase is mitosis, and is the portion of the cell cycle during which the cell is undergoing division. As a result, it is not part of interphase.

Example Question #111 : Gre Subject Test: Biology

Cells that rarely divide, if at all, will spend most of their time in what phase of the cell cycle?

Possible Answers:

G0

G2

S

G1

Correct answer:

G0

Explanation:

When the cell is not preparing to divide any time soon, it will spend its time in the G0 phase. This phase is distinct from the actual cell cycle, and can prevent the cell from actively growing and preparing for division. Cells arrested in the G0 phase are considered quiescent.

Example Question #2 : The Cell Cycle

Which stage of the cell cycle is not part of interphase?

Possible Answers:

Cytokinesis

All of these are part of interphase

S phase

Correct answer:

Cytokinesis

Explanation:

Interphase includes S phase plus the two gap phases . The M phase is the remainder of the cell cycle, made up of mitosis (and meiosis in germ cells) and cytokinesis. Cytokinesis (physical cell division) occurs at the end of M phase, but before interphase.

Example Question #3 : The Cell Cycle

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-dependent kinase (CDK) proteins

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

Controlled expression and degradation of various cyclin 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 #1 : The Cell Cycle

Cytokinesis begins during which phase of mitosis?

Possible Answers:

Telophase

Metaphase

Prometaphase

Anaphase

Prophase

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).

Example Question #5 : The Cell Cycle

A scientist has discovered a mutation that prevents cells from passing anaphase of mitosis. Of the following options, which is the most likely target of the mutation?

Possible Answers:

Proteins involved in chromosome condensation

Myosin

Microtubule formation

Actin synthesis

Correct answer:

Microtubule formation

Explanation:

If the cell cannot progress past metaphase, the cell is most likely having trouble separating the sister chromatids. This process is mediated by attaching the kinetochore microtubules to the kinetochore on the sister chromatids. Our most likely explanation for a problem proceeding past metaphase is that the mutation is affecting the formation of microtubules. The progression from metaphase to anaphase is regulated by the metaphase checkpoint in the cell cycle, which is used to ensure proper attachment of spindle fibers to the centromeres. Problems with spindle fiber formation and binding would cause the cell to be arrested in metaphase.

Actin and myosin are not directly involved in this portion of mitosis, but are very important during cytokinesis. Chromosome condensation has already occurred (during prophase), so our mutation cannot be affecting those proteins.

Example Question #1 : The Cell Cycle

Which phase of mitosis involves the separation of chromatids?

Possible Answers:

Anaphase

Telophase

Prophase

Metaphase

Correct answer:

Anaphase

Explanation:

Cellular division usually takes place in four steps before undergoing cytokinesis. In prophase, the chromosomes condense and become visible, and the spindle apparatus begins to form. In metaphase, the chromosomes line up on the equator of the cell. In anaphase, the chromatids are pulled apart and separated to opposite sides of the cell. Finally, telophase involves the nuclear membrane reforming around the chromosomes, which begin to decondense.

Example Question #1 : The Cell Cycle

Which phase of mitosis is characterized by the reappearance of the nuclear envelope?

Possible Answers:

Anaphase

Telophase

Prophase

Metaphase

Correct answer:

Telophase

Explanation:

Once the cell has split and transported its sister chromatids to opposite ends of the cell, the nuclear envelopes can begin to regenerate around the genetic material at each pole. This event occurs during the end of mitosis, commonly known as telophase.

Example Question #6 : The Cell Cycle

Combrestatin is a drug that prevents the polymerization of microtubules. Which of the following processes would be most affected by combrestatin?

Possible Answers:

Mitosis

DNA synthesis

Membrane depolarization

Muscle contraction

Protein synthesis

Correct answer:

Mitosis

Explanation:

Combrestatin interferes with the formation of microtubules, which make up the cytoskeletal architecture of a cell; therefore, the correct answer choice is involved with some microtubule-based process. DNA and protein synthesis do not involve microtubules, and would not be affected by the lack thereof. Muscle contraction depends on myosin, actin, troponin, etc., and not on microtubules. Membrane depolarization involves sodium/potassium channels, neurotransmitters, etc., and is not directly affected by microtubule inhibition.

The only answer that remains is mitosis, which involves microtubules in chromosomal segregation. The mitotic spindle in this separation is primarily composed of microtubules. The polymerization and depolymerization of microtubules is crucial for mitotic division. Combrestatin therefore prevents proper mitosis.

Example Question #2 : The Cell Cycle

Crossing over occurs during which stage of meiosis?

Possible Answers:

Anaphase I

Metaphase II

Prophase I

Metaphase I

Prophase II

Correct answer:

Prophase I

Explanation:

In the process of meiosis, crossing over (the exchange of genetic material between homologous chromosomes resulting in recombination) only occurs during prophase I, when pairs of homologous chromosomes recombine during synapsis. This contributes to the increase in diversity due to sexual reproduction.

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