Chapter 12- The Cell Cycle

Question 1

Starting with a fertilized egg (zygote), a series of five cell divisions would produce an early embryo with how many cells?
A) 4
B) 8
C) 16
D) 32
E) 64

Answer 1

32

Question 2

If there are 20 chromatids in a cell, how many centromeres are there?
A) 10
B) 20
C) 30
D) 40
E) 80

Answer 2

20

Question 3

The following question(s) are based on the accompanying figure.
In the figure, mitosis is represented by which numbered part(s) of the cycle?
A) I
B) II
C) III
D) IV
E) V

Answer 3

IV

Question 4

In the figure, G1 is represented by which numbered part(s) of the cycle?
A) I or V
B) II or IV
C) III only
D) IV only
E) V only

Answer 4

I or V

Question 5

In the figure, which number represents DNA synthesis?
A) I
B) II
C) III
D) IV
E) V

Answer 5

II

Question 6

In the figure, which number represents the point in the cell cycle during which the
chromosomes are replicated?
A) I
B) II
C) III
D) IV
E) V

Answer 6

II

Question 7

In the figure, at which of the numbered regions would you expect to find cells at
metaphase?
A) I and IV
B) II only
C) III only
D) IV only
E) V only

Answer 7

III only

Question 8

The data were obtained from a study of the length of time spent in each phase of the cell cycle by cells of three eukaryotic organisms designated beta, delta, and gamma.

Of the following, the best conclusion concerning the difference between the S phases for beta and gamma is that ________.
A) gamma contains more DNA than beta
B) beta and gamma contain the same amount of DNA
C) beta cells reproduce asexually
D) beta are in the G0 phase
E) beta is a plant cell and gamma is an animal cell

Answer 8

gamma contains more DNA than beta

Question 9

The best conclusion concerning delta is that the cells ____.
A) contain no DNA
B) contain no RNA
C) contain only one chromosome that is very short
D) are in the G0 phase
E) divide in the G1 phase

Answer 9

are in the G0 phase

Question 10

Researchers pulsed rapidly dividing cultured cells with radioactive thymidine for 30 minutes. 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) Radiolabeled compounds are somewhat cytotoxic, and cell division was initially inhibited.
B) 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.
C) The 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) There seems to be a gap or a lag in the cell cycle, between the synthesis of DNA and cell division.

Answer 10

There seems to be a gap or a lag in the cell cycle, between the synthesis of DNA and cell division.

Question 11

Scientists isolate cells in various phases of the cell cycle. They find a group of cells that have times more DNA than G1 phase cells. The cells of this group are ________.
A) between the G1 and S phases in the cell cycle
B) in the G2 phase of the cell cycle
C) in the M phase of the cell cycle
D) in the S phase of the cell cycle

Answer 11

in the S phase of the cell cycle

Question 12

The first gap in the cell cycle (G1) corresponds to ________.
A) normal growth and cell function
B) the phase in which DNA is being replicated
C) the beginning of mitosis
D) the phase between DNA replication and the M phase

Answer 12

normal growth and cell function

Question 13

Measurements of the amount of DNA per nucleus were taken on a large number of cells from a growing fungus. The measured DNA levels ranged from 3 to 6 picograms per nucleus. In which stage of the cell cycle did the nucleus contain 6 picograms of
DNA?
A) G0
B) G1
C) S
D) G2
E) M

Answer 13

G2

Question 14

A group of cells is assayed for DNA content immediately following mitosis and is
found to have an average of 8 picograms of DNA per nucleus. How many picograms
would be found at the end of S and the end of G2?
A) 8; 8
B) 8; 16
C) 16; 8
D) 16; 16
E) 12; 16

Answer 14

16; 16

Question 15

Nucleotides can be radiolabeled before they are incorporated into newly forming DNA and, therefore, can be assayed to track their incorporation. In a set of experiments, a student—faculty research team used labeled T nucleotides and introduced these into
the culture of dividing human cells at specific times.

Which of the following questions might be answered by using the method described?
A) How many cells are produced by the culture per hour?
B) What is the length of the S phase of the cell cycle?
C) When is the S chromosome synthesized?
D) How many picograms of DNA are made per cell cycle?
E) When do spindle fibers attach to chromosomes?

Answer 15

What is the length of the S phase of the cell cycle?

Question 16

The research team used their experiments to study the incorporation of labeled nucleotides into a culture of lymphocytes and found that the lymphocytes incorporated the labeled nucleotide at a significantly higher level after a pathogen was introduced into the culture. They concluded that ________.
A) the presence of the pathogen made the experiments too contaminated to trust the
results
B) their tissue culture methods needed to be relearned
C) infection causes lymphocytes to divide more rapidly
D) infection causes cell cultures in general to reproduce more rapidly
E) infection causes lymphocyte cultures to skip some parts of the cell cycle

Answer 16

infection causes lymphocytes to divide more rapidly

Question 17

In eukaryotic cells, chromosomes are composed of ________.
A) DNA and RNA
B) DNA only
C) DNA and proteins
D) DNA and phospholipids

Answer 17

DNA and proteins

Question 18

A cell in late anaphase of mitosis will have ________.
A) no chromosomes in the center of the cell
B) chromosomes clustered at one end of the cell
C) individual chromatids beginning to separate from one another
D) chromosomes clustered tightly at the center
E) one large nuclear envelope

Answer 18

no chromosomes in the center of the cell

Question 19

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

Answer 19

cleavage furrow formation and cytokinesis

Question 20

The microtubule-organizing center found in animal cells is an identifiable structure present during all phases of the cell cycle. Specifically, it is known as the ________.
A) microtubulere
B) centrosome
C) centromere
D) kinetochore

Answer 20

centrosome

Question 21

In human and many other eukaryotic species’ cells, the nuclear membrane has to disappear to permit ________.
A) cytokinesis
B) the attachment of microtubules to kinetochores
C) the splitting of the centrosomes
D) the disassembly of the nucleolus

Answer 21

the attachment of microtubules to kinetochores

Question 22

The mitotic spindle is a microtubular structure that is involved in ________.
A) splitting of the cell (cytokinesis) following mitosis
B) triggering the compaction and condensation of chromosomes
C) dissolving the nuclear membrane
D) separation of sister chromatids

Answer 22

separation of sister chromatids

Question 23

Kinetochore microtubules assist in the process of splitting centromeres by ________.
A) using motor proteins to split the centromere at specific arginine residues
B) creating tension by pulling toward opposite poles
C) sliding past each other like actin filaments
D) phosphorylating the centromere, thereby changing its conformation

Answer 23

creating tension by pulling toward opposite poles

Question 24

Mitosis separates chromosomes. Cytoplasm is divided between two daughter cells by ________.
A) cloning
B) cytokinesis
C) binary fission
D) the formation of kinetochores

Answer 24

cytokinesis

Question 25

Some cells have several nuclei per cell. How could such multinucleated cells be explained?
A) The cell underwent repeated cytokinesis but no mitosis.
B) The cell underwent repeated mitosis with simultaneous cytokinesis.
C) The cell underwent repeated mitosis, but cytokinesis did not occur.
D) The cell had multiple S phases before it entered mitosis.

Answer 25

The cell underwent repeated mitosis, but cytokinesis did not occur.

Question 26

Which cytoskeletal proteins are important constituents of the contractile structures that form the cleavage furrows involved in animal cell cytokinesis?
A) actin
B) dynein
C) tubulin
D) myosin

Answer 26

actin

Question 27

How is plant cell cytokinesis different from animal cell cytokinesis?
A) The contractile filaments found in plant cells are structures composed of carbohydrates; the cleavage furrow in animal cells is composed of contractile phospholipids.
B) Plant cells deposit vesicles containing cell-wall building blocks on the metaphase plate; animal cells form a cleavage furrow.
C) The structural proteins of plant cells separate the two cells; in animal cells, a cell membrane separates the two daughter cells.
D) Plant cells divide after metaphase but before anaphase; animal cells divide after anaphase.

Answer 27

Plant cells deposit vesicles containing cell-wall building blocks on the metaphase plate; animal cells form a cleavage furrow.

Question 28

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) Vesicles containing plasma membrane constituents are transported to the metaphase plate, where cytokinesis takes place.
B) Excess cytoplasm is removed.
C) The cleavage furrow deepens.
D) Two new daughter nuclei form.

Answer 28

The cleavage furrow deepens.

Question 29

FtsZ is a bacterial cytoskeletal protein that 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 mitotic spindle of eukaryotic cells
D) the microtubule-organizing center of eukaryotic cells

Answer 29

the cleavage furrow of eukaryotic animal cells

Question 30

At which phase are centrioles beginning to move apart in animal cells?
A) telophase
B) anaphase
C) prometaphase
D) metaphase
E) prophase

Answer 30

prophase

Question 31

Taxol is an anticancer drug extracted from the Pacific yew tree. In animal cells, Taxol disrupts microtubule formation. Surprisingly, this stops mitosis. Specifically, Taxol must affect ________.
A) the structure of the mitotic spindle
B) anaphase
C) formation of the centrioles
D) chromatid assembly
E) the S phase of the cell cycle

Answer 31

the structure of the mitotic spindle

Question 32

Which of the following are primarily responsible for cytokinesis in plant cells but not in animal cells?
A) kinetochores
B) Golgi-derived vesicles
C) actin and myosin
D) centrioles and centromeres
E) tubulin and dynein

Answer 32

Golgi-derived vesicles

Question 33

Movement of the chromosomes during anaphase would be most affected by a drug that prevents ________.
A) nuclear envelope breakdown
B) cell-wall formation
C) elongation of microtubules
D) shortening of microtubules
E) formation of a cleavage furrow

Answer 33

shortening of microtubules

Question 34

During which phase of mitosis do the chromatids become chromosomes?
A) telophase
B) anaphase
C) prophase
D) metaphase
E) cytokinesis

Answer 34

anaphase

Question 35

The unlettered circle at the top of the accompanying figure shows a diploid nucleus with four chromosomes that have not yet replicated. There are two pairs of homologous chromosomes, one long and the other short. One haploid set is black, and the other is gray. The circles labeled A to E show various combinations of these chromosomes.

What is the correct chromosomal condition at prometaphase of mitosis?
A) A
B) B
C) C
D) D
E) E

Answer 35

B

Question 36

What is the correct chromosomal condition for one daughter nucleus at telophase of mitosis?
A) A
B) B
C) C
D) D
E) E

Answer 36

E

Question 37

If the cell whose nuclear material is shown in the accompanying figure continues toward completion of mitosis, which of the following events would occur next?
A) cell-membrane synthesis
B) spindle fiber formation
C) nuclear envelope breakdown
D) formation of telophase nuclei
E) synthesis of chromatids

Answer 37

formation of telophase nuclei

Question 38

Through a microscope, you can see a cell plate beginning to develop across the
middle of a cell and nuclei forming on either side of the cell plate. This cell is most likely ________.
A) an animal cell in the process of cytokinesis
B) a plant cell in the process of cytokinesis
C) an animal cell in the S phase of the cell cycle
D) a bacterial cell dividing
E) a plant cell in metaphase

Answer 38

a plant cell in the process of cytokinesis

Question 39

Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to ________.
A) disruption of mitotic spindle formation
B) inhibition of regulatory protein phosphorylation
C) suppression of cyclin production
D) myosin denaturation and inhibition of cleavage furrow formation
E) inhibition of DNA synthesis

Answer 39

disruption of mitotic spindle formation

Question 40

In the cells of some organisms, mitosis occurs without cytokinesis. This results in ________.
A) cells with more than one nucleus
B) cells that are unusually small
C) cells lacking nuclei
D) destruction of chromosomes
E) cell cycles lacking an S phase

Answer 40

cells with more than one nucleus

Question 41

Which of the following does NOT occur during mitosis?
A) condensation of the chromosomes
B) replication of the DNA
C) separation of sister chromatids
D) spindle formation
E) separation of the spindle poles

Answer 41

condensation of the chromosomes

Question 42

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

Answer 42

They are involved in the disassembly of the nuclear envelope.

Question 43

The product of the p53 gene ________.
A) inhibits the cell cycle
B) slows down the rate of DNA replication by interfering with the binding of DNA polymerase
C) causes cells to reduce expression of genes involved in DNA repair
D) allows cells to pass on mutations due to DNA damage

Answer 43

inhibits the cell cycle

Question 44

In the accompanying figure, MPF reaches its highest concentration during this stage.
A) I
B) II
C) III
D) IV
E) V

Answer 44

III

Question 45

What happens if MPF (mitosis-promoting factor) is introduced into immature frog oocytes that are arrested in G2?
A) Nothing happens.
B) The cells undergo meiosis.
C) The cells enter mitosis.
D) Cell differentiation is triggered.

Answer 45

The cells enter mitosis.

Question 46

Once a cell completes mitosis, molecular division triggers must be turned off. What happens to MPF during mitosis?
A) It is completely degraded.
B) It is exported from the cell.
C) The cyclin component of MPF is degraded.
D) The Cdk component of MPF is degraded and exported from the cell.

Answer 46

The cyclin component of MPF is degraded.

Question 47

The M-phase checkpoint ensures that all chromosomes are attached to the mitotic
spindle. If this does NOT happen, cells would most likely be arrested in ________.
A) telophase
B) prophase
C) prometaphase
D) metaphase

Answer 47

metaphase

Question 48

If a cell has accumulated DNA damage, it is unlikely to ________.
A) pass the G2 checkpoint
B) activate DNA repair mechanisms
C) enter G1 from mitosis
D) synthesize cyclin-dependent kinases

Answer 48

pass the G2 checkpoint

Question 49

Regulatory proteins that prevent a cell from entering the S phase under conditions of DNA damage are also known as ________.
A) cyclins
B) cyclin-dependent kinases
C) antibodies
D) tumor suppressors

Answer 49

tumor suppressors

Question 50

Proteins that are involved in the regulation of the cell cycle and that show fluctuations in concentration during the cell cycle are called ________.
A) ATPases
B) kinetochores
C) kinases
D) estrogen receptors
E) cyclins

Answer 50

cyclins

Question 51

The MPF protein complex turns itself off by ________.
A) activating a process that destroys cyclin components
B) activating an enzyme that stimulates cyclin
C) binding to chromatin
D) exiting the cell
E) activating the anaphase-promoting complex

Answer 51

activating a process that destroys cyclin components

Question 52

Cyclin-dependent kinase (Cdk) is ________.
A) inactive, or “turned off,” in the presence of cyclin
B) present only during the S phase of the cell cycle
C) an enzyme that removes hydroxyl groups from growth hormones
D) the enzyme that catalyzes the attachment of chromosomes to microtubules
E) an enzyme that attaches phosphate groups to other proteins

Answer 52

an enzyme that attaches phosphate groups to other proteins

Question 53

Neurons and some other specialized cells divide infrequently because they ________.
A) no longer have active nuclei
B) no longer carry receptors for signal molecules
C) have entered into G0
D) can no longer bind Cdk to cyclin
E) show a drop in MPF concentration

Answer 53

have entered into G0

Question 54

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

Answer 54

activates a Cdk molecule when it is in sufficient concentration

Question 55

The decline of MPF activity at the end of mitosis is due to ________.
A) the destruction of the protein kinase Cdk
B) decreased synthesis of Cdk
C) the degradation of cyclin
D) the accumulation of cyclin
E) synthesis of DNA

Answer 55

the degradation of cyclin

Question 56

Tumor suppressor genes ________.
A) are frequently overexpressed in cancerous cells
B) are cancer-causing genes introduced into cells by viruses
C) encode proteins that help prevent uncontrolled cell growth
D) often encode proteins that stimulate the cell cycle

Answer 56

encode proteins that help prevent uncontrolled cell growth

Question 57

BRCA1 and BRCA2 are considered to be tumor suppressor genes because ________.
A) they prevent infection by tumor viruses that cause cancer
B) their normal products participate in repair of DNA damage
C) the mutant forms of either one of these prevent breast cancer
D) the normal genes make estrogen receptors
E) they block penetration of breast cells by chemical carcinogens

Answer 57

their normal products participate in repair of DNA damage

Question 58

The cancer-causing forms of the Ras protein are involved in which of the following processes?
A) relaying a signal from a growth-factor receptor
B) DNA replication
C) DNA repair
D) cell—cell adhesion
E) cell division

Answer 58

relaying a signal from a growth-factor receptor

Question 59

Forms of the Ras protein found in tumors usually cause which of the following?
A) DNA replication to stop
B) DNA replication to be hyperactive
C) cell-to-cell adhesion to be nonfunctional
D) cell division to cease
E) excessive cell division

Answer 59

excessive cell division