Deck 12: The Cell Cycle

Question 1

In a culture of cells, it is observed that the cell cycle has arrested stopped) during the G1 phase. The reason for this could be that

A) not all components needed for DNA replication are present.
B) not all components needed for mitosis are present.
C) not all chromosomes have been replicated.
D) not all chromosomes are attached to mitotic spindles.

Answer 1

not all components needed for DNA replication are present.

Question 2

The microtubular organizing center found in animal cells is an identifiable structure present during all phases of the cell cycle. Specifically, it is known as which of the following?

A) kinetochore
B) cell plate
C) centrosome
D) centromere

Answer 2

C

Question 3

Metaphase occurs prior to the splitting of centromeres. It is characterized by

A) aligning of chromosomes on the equator.
B) disassembly of the nuclear envelope.
C) duplication of centrioles.
D) cytokinesis.

Answer 3

A

Question 4

Figure 12.1
Based on structures present in the figure above, this cell is in which substage of interphase?

A) G₀ phase
B) G₂ phase
C) S phase
D) G₁ phase

Question 5

DNA is composed of four nucleosides: adenosine, cytidine, thymidine, and guanosine. If scientists introduced radioactive thymidine into the growth medium of the cells, it would be incorporated into the DNA molecule

A) at any point in the cell cycle.
B) during DNA replication.
C) as the cell enters G₁ of interphase.
D) when centromeres split so the two chromosomes can be separated.

Question 6

Researchers pulsed rapidly dividing cultured cells for 30 minutes with radioactive thymidine. The cells were then exposed to a solution containing non- radiolabeled thymidine. Cells were analyzed at 2- hour intervals. At the 2- hour time point, no cells appeared to be dividing. Only after 4 hours did some labeled cells appear to be in M phase. This result can be explained in the following way:

A) The cells were arrested in a nondividing state because of the treatment and could not enter M phase until several hours after the label was removed.
B) There seems to be a gap or a lag in the cell cycle, between the synthesis of DNA and cell division.
C) Synthesis S) phase is lengthy-about 12 hours in most cell types-and the radioactive thymidine was not present long enough for most cells to be labeled.
D) Cultured cells all divide at the same time, and none synthesized DNA during the 30- minute labeling period.

Question 7

The mitotic spindle is a microtubular structure that is involved in

A) separation of sister chromatids.
B) disassembly of the nucleolus.
C) triggering the compaction and condensation of chromosomes.
D) splitting of the cell cytokinesis) following mitosis.

Question 8

How is plant cell cytokinesis different from animal cell cytokinesis?

A) Plant cells deposit vesicles containing cell- wall building blocks on the metaphase plate; animal cells form a cleavage furrow.
B) The cleavage furrow in animal cells is composed of protein contractile filaments; the contractile filaments found in plant cells are structures composed of carbohydrates.
C) Animal cells have centrosomes that are involved in this process, but plant cells have microtubular organizing centers that are not detectable during most of the cell cycle.
D) The structural carbohydrates of the plant cells separate the two cells, whereas in animal cells, a cell membrane separates the two daughter cells.

Question 9

Myosin is a motor protein involved in animal cell cytokinesis. It binds to ATP or ADP, causing the myosin to move with respect to actin. What is the effect of the interaction between myosin and actin?

A) Excess cytoplasm is removed.
B) Vesicles containing plasma membrane constituents are transported to the metaphase plate, where cytokinesis takes place.
C) The cleavage furrow deepens.
D) It triggers the reformation of the daughter nuclei.

Question 10

The first gap in the cell cycle G₁) corresponds to

A) the beginning of mitosis.
B) the phase in which DNA is being replicated.
C) normal growth and functioning.
D) the phase between DNA replication and the M phase.

Question 11

Scientists isolate cells in various phases of the cell cycle. They find a group of cells that have 1½ times more DNA than G₁ phase cells. The cells of this group are in

A) the process of cytokinesis.
B) S phase.
C) M phase.
D) the G₂ phase of the cell cycle.

Question 12

Which cytoskeletal proteins are important constituents of the contractile structures that form the cleavage furrows involved in animal cell cytokinesis?

A) elastin
B) dynein
C) actin
D) tubulin

Question 13

Mitosis is the process of chromosome separation. Cytoplasm is divided between the two daughter cells in a process known as

A) karyokinesis.
B) G₁ phase.
C) S phase.
D) cytokinesis.

Question 14

In human and many other eukaryotic species' cells, the nuclear membrane has to disappear in order for what to take place?

A) cytokinesis
B) attachment of mitotic spindle to kinetochores
C) disassembly of the nucleolus
D) splitting of the centrosomes

Question 15

Some cells have several nuclei per cell. How might such multinucleated cells arise?

A) repeated mitosis with concomitant cytokinesis
B) multiple S phases before the entry of a cell into mitosis
C) repeated mitosis without cytokinesis
D) repeated cytokinesis with no mitosis

Question 16

Following the attachment of spindle microtubules to kinetochores, chromosomes are moved around by

A) motor activity taking place in the centrosomes.
B) elongation and shortening of microtubules.
C) histones.
D) myosin motor proteins.

Question 17

A parent cell divides to form two genetically identical daughter cells in the process of mitosis. For mitosis to take place

A) the parent cell must reproduce its DNA during telophase.
B) the parent cell must replicate its entire genome prior to mitosis.
C) the parent cell must first be fertilized.
D) the parent cell must divide its DNA in half so each daughter cell gets only the genes needed to carry out its functions. In this way, differentiation occurs.

Question 18

At the end of mitosis, each G₁ daughter cell has

A) identical DNA to that of the G₁ parent cell.
B) twice the cytoplasm and the same amount of DNA as the G₁ parent cell.
C) twice the DNA and half the cytoplasm of the G₁ parent cell.
D) half the DNA and half the cytoplasm of the G₁ parent cell.

Question 19

In the figure provided, G₁ is represented by which numbered parts) of the cycle?

A) V only
B) III only
C) IV only
D) I or V
E) II or IV

Question 20

How might spindle microtubules assist in the process of splitting centromeres?

A) coding for enzymes involved in the process
B) creating tension by pulling toward opposite poles
C) the use of motor proteins to split the centromere at specific arginine residues
D) phosphorylating the centromere, which changes its conformation

Question 21

The drug cytochalasin B blocks the function of actin. Which of the following aspects of the cell cycle would be most disrupted by cytochalasin B?

A) spindle attachment to kinetochores
B) cleavage furrow formation and cytokinesis
C) cell elongation during anaphase
D) spindle formation
E) DNA synthesis

Question 22

Regulatory proteins that serve to prevent a cell from entering the S phase under conditions of DNA damage are also known as

A) antibodies.
B) tumour suppressors.
C) cyclin- dependent kinases.
D) cyclins.

Question 23

If a cell has accumulated DNA damage, it is unlikely to

A) pass the G₂ checkpoint.
B) synthesize cyclin- dependent kinases.
C) activate DNA repair mechanisms.
D) enter G₁ from mitosis.

Question 24

The M- phase checkpoint is designed to make sure all chromosomes are attached to the mitotic spindle. If this fails to happen, in which stage of mitosis would the cells be most likely to arrest?

A) prometaphase
B) metaphase
C) telophase
D) prophase

Question 25

Which of the following is not an effect of mitosis- promoting factor MPF) involved in moving a cell into M phase?

A) phosphorylation of lamins, initiating breakdown of the nuclear membrane
B) phosphorylation of an enzyme that breaks down the cyclin molecule
C) phosphorylation of microtubule associated proteins, triggering the formation of the mitotic spindle
D) degradation of cyclin- dependent kinase

Question 26

Masses of noninvasive cells that remain at their site of origin are known as _ tumours.

A) benign
B) malignant
C) secondary
D) metastatic

Question 27

At which stage does chromosome organization change from diffuse/uncondensed to a compact/condensed state?

A) interphase
B) prophase
C) telophase
D) metaphase
E) anaphase

Question 28

What happens when MPF mitosis- promoting factor) is introduced into immature frog oocytes that are arrested in G₂?

A) Cell differentiation is triggered.
B) The cells enter mitosis.
C) Fertilization occurs.
D) Nothing happens.

Question 29

A cyclin

A) activates a Cdk molecule when its concentration is decreased.
B) is present in similar concentrations throughout the cell cycle.
C) activates a Cdk molecule when it is in sufficient concentration.
D) decreases in concentration when M phase-promoting factor MPF) activity increases.
E) is activated by binding to microtubules.

Question 30

For cells to divide more rapidly, increased production would likely be required of each of the following proteins EXCEPT

A) activated MPF.
B) p53.
C) cyclins.
D) PDGF.

Question 31

Once researchers understood that chromosomes are moved by the spindle microtubules, the next question they wanted to answer is how the microtubules function to bring about this process. They used fluorescent labels to make the chromosomes and the microtubular structures fluoresce. When anaphase began centromeres split), they photobleached a section of microtubules. As chromosomes moved toward the poles of the daughter cells, the photobleached sections of the microtubules remained stationary. This result suggests that

A) the microtubules elongate and shorten at the centrosome end.
B) the microtubules elongate and shorten at their kinetochore end.
C) the microtubules are of constant length; centrosomes move farther apart to separate chromosomes.
D) the microtubules overlap and slide with respect to each other, effectively shortening the microtubules without depolymerizing the actual fiber.

Question 32

Cancer- causing mutated tumour suppressor genes result from which of the following?

A) mutations in genes encoding proteins that normally inhibit progression through the cell cycle
B) mutations that cause overexpression of genes encoding proteins that normally stimulate progression through the cell cycle
C) cell- contact inhibition
D) programmed cell death

Question 33

FtsZ is a bacterial cytoskeletal protein. It forms a contractile ring involved in bacterial cytokinesis. Its function is analogous to

A) the cleavage furrow of eukaryotic animal cells.
B) the cell plate of eukaryotic plant cells.
C) the microtubular organizing center of eukaryotic cells.
D) the mitotic spindle of eukaryotic cells.

Question 34

In the process of chromosome separation, how do microtubules maintain contact with the kinetochores and shorten at the same time?

A) Motor proteins move chromosomes down the microtubular structures of the mitotic spindle.
B) The centrosomes move apart, so the microtubular proteins do not need to shorten.
C) Actin microfilaments cause the microtubular proteins to slide past each other.
D) The centrosomes cause the shortening and depolymerization of the microtubular proteins.

Question 35

Exposure of zebrafish nuclei to meiotic cytosol resulted in phosphorylation of NEP55 and L68 proteins by cyclin- dependent kinase 2. NEP55 is a protein of the inner nuclear membrane, and L68 is a protein of the nuclear lamina. What is the most likely role of phosphorylation of these proteins in the process of mitosis?

A) They assist in the movement of the centrosomes to opposite sides of the nucleus.
B) They enable the attachment of the spindle microtubules to kinetochore regions of the centromere.
C) They are involved in the disassembly and dispersal of the nucleolus.
D) They are involved in the disassembly of the nuclear envelope.

Question 36

Nerve cells lose their ability to undergo mitosis. Instead, they are permanently stuck in

A) S of interphase.
B) G₂.
C) G₀.
D) meiosis.

Question 37

Once a cell completes mitosis, molecular division triggers must be turned off. What happens to MPF during mitosis?

A) Cyclin is degraded; the concentration of cyclin- dependent kinase remains unchanged, but without cyclin, MPF is not formed.
B) The cyclin- dependent kinases take on a function unrelated to mitosis.
C) It is completely degraded.
D) Cyclin- dependent kinase is degraded; cyclin concentration remains constant, but without cyclin- dependent kinase, MPF is not formed.

Question 38

Which of the following is NOT involved in the regulation of the eukaryotic cell cycle?

A) ribosomes
B) cyclins
C) hormones
D) cyclin- dependent kinases CDKs)
E) p53

Question 39

Which of the following statements is FALSE with respect to both bacterial binary fission and eukaryotic mitotic cell division?

A) The nuclear envelope must disintegrate before the spindle apparatus can move the chromosomes.
B) DNA must be replicated prior to division.
C) Daughter cells must contain the same hereditary material as one another and the parent cell.
D) Cytoplasmic materials must be distributed to each of the daughter cells.