GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Mitosis

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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Example Questions

Example Question #1 : Help With Mitosis

During mitosis, what proteins are involved in the formation of the contractile ring?

Possible Answers:

Kinetochore microtubules and kinesin

Actin and dyenin

Polar microtubules and dyenin

Actin and myosin-2

Correct answer:

Actin and myosin-2

Explanation:

The contractile ring is made up of actin and myosin-2 and is used to initiate cytokinesis. Polar and kinetochore microtubules have important functions during earlier stages of mitosis. Polar microtubules interact within the cytoplasm during metaphase and anaphase, while kinectochore microtubules directly attach to chromosome centromeres to facilitate separation. Dyenin is a motor protein that interacts with microtubules to aid in protein transport.

Example Question #2 : Help With Mitosis

Which phase of mitosis is characterized by the alignment of sister chromatids at the center of the cell?

Possible Answers:

Anaphase

Telophase

Prophase

Metaphase

Correct answer:

Metaphase

Explanation:

During mitosis, sister chromatids will line up in the center of the cell so that they may be pulled to opposite ends by the spindle fibers. This lining up takes place in the second phase of mitosis: metaphase.

Example Question #3 : Help With Mitosis

Blocking which of the following processes is likely to directly interfere with cyclins' role to regulate the cell cycle?

Possible Answers:

Ubiquitination

Microtubule formation

Replication

Endocytosis

Correct answer:

Ubiquitination

Explanation:

Cyclin proteins fluctuate in level during the different stages of the cell cycle (except for Cyclin D). For example, Cyclin E regulates the entry into S phase. The expression of the cyclin E gene increases, which leads to higher Cyclin E protein levels in the cell. After the cell passes S phase, Cyclin E protein is actively destroyed by ubiquitination. 

When Cyclins are bound to Cdks, they can regulate the activity of proteins that regulate processes like replication and microtubule formation; however, of the cellular processes listed, blocking ubiquitination would be the only process that would directly interfere with cyclins' role to regulate the cell cycle as cyclin proteins need to be destroyed at the correct time to allow the cell cycle to progress.

Example Question #4 : Help With Mitosis

What proteins do cyclins regulate and how do these proteins carry out their catalytic activities during cell cycle progression?

Possible Answers:

Cyclins regulate cyclin-dependent kinase inhibitors (CKIs). CKIs phosphorylate their substrates to effect activity.

Cyclins regulate cyclin-dependent kinases (CDKs). CDKs dephosphorylate their substrates to effect activity.

Cyclins regulate cyclin-dependent kinase inhibitors (CKIs). CKIs dephosphorylate their substrates to effect activity.

Cyclins do not play a role in cell cycle progression

Cyclins regulate cyclin-dependent kinases (CDKs). CDKs phosphorylate their substrates to effect activity.

Correct answer:

Cyclins regulate cyclin-dependent kinases (CDKs). CDKs phosphorylate their substrates to effect activity.

Explanation:

Kinases are proteins that phosphorylate their substrates, often activating these substrates. In the context of cell cycle progression, cyclins interact with cyclin-dependent kinases (CDKs) and activate the CDK kinase domain to phosphorylate substrates and promote cell cycle progression. CDK inhibitors interact with CDKs to inhibit the CDK kinase domain from phosphorylating substrates. 

Example Question #5 : Help With Mitosis

During what stage of cellular mitosis do the microtubules attach to the centromeres to eventually align the chromosomes?

Possible Answers:

Prometaphase

Prophase

Interphase

Anaphase

Telophase

Correct answer:

Prometaphase

Explanation:

The correct answer is prometaphase, in which the nuclear membrane dissolves and the microtubules attach to the centromeres. Interphase occurs before mitosis begins, and includes S phase, where the chromosomes are duplicated. In anaphase, the chromosome duplicates are separated by the microtubules. In telophase, cell division begins with the newly separated chromosome copies.

Example Question #6 : Help With Mitosis

The contractile ring constricts the cell membrane to form a cleavage furrow during cytokinesis. What is the contractile ring composed of?  

Possible Answers:

Microtubules 

Lamin 

Myosin and actin filaments 

Myosin and tubulin 

Adenosine triphosphate

Correct answer:

Myosin and actin filaments 

Explanation:

The correct answer is myosin and actin filaments. Myosin hydrolyzes adenosine triphosphate (ATP) and moves along the actin filaments previously assembled at the cell cortex, constricting the actin and the plasma membrane. Lamin is found in the nucleus and gives structural support to the nuclear membrane. Tubulin and microtubules are components of the cell cytoskeleton. 

Example Question #7 : Help With Mitosis

A certain line of cells has a mutated, non-functioning copy of the enzyme DNA ligase. What portion of the DNA would be affected by this mutated enzyme?

Possible Answers:

Minor groove

DNA polymerase

Major groove

The leading strand

The lagging strand

Correct answer:

The lagging strand

Explanation:

DNA ligase is an enzyme used to link DNA via the formation of a phosphodiester bond. During lagging strand synthesis, DNA ligase connects the okazaki fragments. Without this enzyme functioning properly, the lagging strand would not be completed.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept
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