Deck 18: The Cell Cycle

Question 1

The eukaryotic cell cycle is composed of four phases in the following order:

A) G₁; S; G₂; M.
B) G₁; G₂; S; M.
C) G₁; M; G₂; S.
D) S; G₁; G₂; M.

Answer 1

A

Question 2

The length of time it takes for the cells labeled during DNA synthesis to begin to enter mitosis is a good estimate of the length of the _______ phase(s).

A) G₁
B) S
C) G₂
D) M

Answer 2

C

Question 3

In a typical cycling mammalian cell, _______ of the cell cycle is spent in interphase.

A) 99%
B) 95%
C) 75%
D) 50%

Answer 3

B

Question 4

Cell cycles of early embryonic animal cells are unusual because they have

A) no G₁ or G₂.
B) an elongated G₁ and G₂.
C) a short S.
D) a much shortened M.

Question 5

The number of cells in the different phases of a population can be determined most easily by using a _______ to measure the amount of DNA per cell in a large sample of cells.

A) scintillation counter
B) flow cytometer
C) fluorescence microscope
D) phase-contrast microscope after autoradiography

Question 6

Cells in the quiescent phase of the cell cycle are said to be in the _______ phase.

A) G₀
B) G₁
C) G₂
D) M

Question 7

Which of the following represents the amount of DNA in a typical G₂ cell?

A) n
B) 2n
C) 4n
D) 8n

Question 8

What event takes place during interphase?

A) Centromeres divide.
B) Metabolic processes, such as DNA replication, are carried out by the cell.
C) Spindle fibers start forming.
D) Centrioles begin to appear.

Question 9

Skin fibroblasts near a wound, arrested in G₀, are stimulated to enter G₁ by _______ growth factor.

A) epidermal
B) fibroblast
C) platelet-derived
D) keratinocyte

Question 10

The oocytes in a normal 7-year-old female (prepubertal) would be expected to be arrested in which stage of the cell cycle, until they are hormonally stimulated?

A) G₁
B) G₂
C) Interphase
D) G₀

Question 11

Progression through the cell cycle in the yeast Saccharomyces cerevisiae is regulated by

A) external signals such as availability of nutrients and mating factors.
B) internal signals such as growth factors and steroid hormones.
C) internal signals such as the availability of glucose and ATP.
D) simple organisms such as yeast do not have a cell cycle.

Question 12

The G₁ checkpoint in budding yeast cells is called

A) START.
B) the restriction point.
C) the decision point.
D) the G₁/S boundary.

Question 13

The G₁ checkpoint in animal cells is called

A) START.
B) the restriction point.
C) the decision point.
D) the G₁/S boundary.

Question 14

The G₂ checkpoint prevents entry into _______ if DNA synthesis is incomplete and/or the DNA is damaged.

A) G₁
B) S
C) G₂
D) M

Question 15

A scientist notices that cells being grown in culture have ceased to divide. Further investigation demonstrates the cells have abnormally segregated chromosomes. Which checkpoint are these cells likely arrested at?

A) Spindle assembly checkpoint
B) DNA damage checkpoint
C) START
D) Restriction checkpoint

Question 16

Maturation promotion factor (MPF), discovered by Masui and Markert, is the factor that

A) is missing in the cdc2 mutant in yeast.
B) induces entry into meiosis when injected into frog oocytes.
C) fluctuates in amount during early cleavages of sea urchin eggs.
D) fluctuates in amount during the cell cycle of mammalian cells.

Question 17

MPF is a

A) monomeric protein kinase.
B) dimer of two molecules of Cdk1.
C) dimer of Cdk1 and cyclin A.
D) dimer of Cdk1 and cyclin B.

Question 18

MPF is a general regulator of the transition from

A) G₁ to S.
B) S to G₂.
C) G₂ to M.
D) metaphase to anaphase.

Question 19

The passage of a cell through the stages of the cell cycle is controlled by protein kinases that phosphorylate many different proteins at appropriate times. What are these protein kinases called?

A) Cdk activating kinases
B) Cyclin-dependent kinases
C) Cyclins
D) Tyrosine kinases

Question 20

Studies on cell cycle mutants in budding and fission yeasts demonstrated that cdc2 and cdc28 both encode a

A) protein kinase.
B) protein phosphatase.
C) ubiquitin ligase.
D) growth factor.

Question 21

Two sea urchin proteins were named cyclin A and B because, during the embryonic cell cycle, they were periodically

A) activated and inactivated by phosphorylation and dephosphorylation.
B) synthesized and degraded.
C) bound and released by another protein.
D) ubiquitylated and nonubiquitylated.

Question 22

To become active, Cdk1 must

A) bind cyclin.
B) bind cyclin and be phosphorylated on tyrosine 15 and threonines 14 and 161.
C) bind cyclin and be phosphorylated on tyrosine 15 and be dephosphorylated on threonines 14 and 161.
D) bind cyclin and be phosphorylated on threonine 161 and be dephosphorylated on threonine 14 and tyrosine 15.

Question 23

Cdks bind to cyclin and are activated by

A) phosphorylation by Wee1.
B) dephosphorylation by Cdc25 protein phosphatase.
C) the binding of Ink4.
D) the binding of Cip.

Question 24

Which cyclin(s) is(are) required to pass the G₁ restriction point in animal cells?

A) Cyclin A
B) Cyclin A and Cyclin B
C) Cyclin D
D) Cyclin D and Cyclin E

Question 25

Passage of animal cells through the cell cycle is regulated primarily by

A) the availability of nutrients.
B) intracellular second messengers.
C) extracellular growth factors.
D) direct cell surface interactions.

Question 26

The retinoblastoma protein (Rb) binds to and inhibits

A) transcription factor E2F.
B) oncogenes.
C) cyclin-dependent kinase.
D) p53.

Question 27

Growth-factor stimulation of the Ras/Raf/MEK/ERK pathway initially stimulates the synthesis of cyclin

A) A.
B) B.
C) E.
D) D.

Question 28

Cells are restricted to one round of DNA replication per cycle by origin of replication binding proteins called

A) ATMs.
B) Akts.
C) Oris.
D) MCMs.

Question 29

To prevent cells with unreplicated DNA from passing through the G₂ checkpoint, Chk1 and Chk2 _______ protein phosphatase Cdc25.

A) phosphorylate and stimulate
B) phosphorylate and inhibit
C) dephosphorylate and stimulate
D) dephosphorylate and induce the degradation of

Question 30

p21 inhibits cell cycle progression by binding to and inhibiting

A) cyclin-dependent kinases.
B) p53.
C) ATM.
D) Rb protein.

Question 31

Damaged DNA is sensed by a complex of proteins that activate the protein kinase

A) ATM or ATR.
B) ABS.
C) Akt.
D) MCM.

Question 32

The disease ataxia telangiectasia, which causes nervous system defects and a high frequency of cancer in affected individuals, results from a mutation in the gene for the protein

A) ATM.
B) ABS.
C) Akt.
D) MCM.

Question 33

Nuclear envelope breakdown occurs at the

A) beginning of prophase.
B) end of prophase.
C) end of prometaphase.
D) beginning of anaphase.

Question 34

Entry into mitosis occurs because

A) cyclin is destroyed at the beginning of mitosis.
B) cyclin is phosphorylated at the beginning of mitosis.
C) sufficient cyclin-dependent kinase is synthesized to trigger mitosis.
D) Cdk1/Cyclin B (MPF) get activated.

Question 35

During prophase, Cdk1/Cyclin B (MPF) directly phosphorylates all of the following except

A) condensins.
B) lamins.
C) APC/C.
D) microtubule-associated proteins.

Question 36

Phosphorylation of the Golgi matrix proteins by Cdk1 during mitosis

A) mediates breakdown of the Golgi apparatus into vesicles.
B) activates proteins to degrade the Golgi proteins.
C) inhibits association of the Golgi with microtubules.
D) causes microtubules to pull the Golgi into two parts.

Question 37

The beginning of anaphase occurs when cohesins, holding the sister chromatids together, are degraded by

A) anaphase-promoting complex.
B) ATM.
C) proteasome.
D) separase.

Question 38

As the cell enters M phase, the condensins are activated as a result of

A) proteolytic cleavage by checkpoint proteases.
B) dephosphorylation by cyclin dependent and Aurora B phosphatases.
C) ubiquitylation by cyclin dependent ubiquitin ligases.
D) phosphorylation by both Cdk1 and Aurora B kinase.

Question 39

The DNA region to which proteins bind to form the kinetochore and spindle fibers attach for segregation of the chromosomes is called the

A) chiasma.
B) centromere.
C) synaptonemal complex.
D) origin.

Question 40

Chromosomes are attached to spindle microtubules by

A) centromeres.
B) kinetochores.
C) centrioles.
D) centrosomes.

Question 41

Polar microtubules

A) overlap in the center of the spindle.
B) are attached to the contractile ring.
C) are attached to kinetochores.
D) pull kinetochores poleward.

Question 42

During mitosis, the rate of microtubule turnover

A) decreases.
B) stays the same.
C) doubles.
D) increases five- to tenfold.

Question 43

During the spindle fiber checkpoint, degradation of _______ allows for separation of the sister chromatids.

A) cyclin B
B) separase
C) cohesin
D) kinetochore

Question 44

The mechanism of cytokinesis in plants involves the formation of the

A) contractile ring.
B) Aurora belt.
C) cell plate.
D) plasma membrane bridge.

Question 45

The progression from metaphase to anaphase results from

A) phosphorylation mediated by Polo-like kinase.
B) ubiquitin-mediated proteolysis of key regulatory proteins.
C) phosphorylation mediated by Cdk2.
D) activation by Wee1.

Question 46

The most variable phase of the cell cycle is _______.

Question 47

The spindle assembly checkpoint monitors the alignment of chromosomes on the _______.

Question 48

Injection of MPF into frog oocytes induces them to enter _______.

Question 49

The degradation of cyclin B during _______ occurs after it becomes modified by the addition of ubiquitin.

Question 50

Separation of anaphase chromosomes begins when _______ is degraded to break the link between sister chromatids.

Question 51

Cyclin B and _______ are ubiquitylated and degraded by active APC/C.

Question 52

Cytokinesis begins during the _______ stage of mitosis.

Question 53

Cell plate formation occurs only in _______ cells.

Question 54

Interphase usually consists of G₁, S, and G₂, but in some cells it consists only of S.

Question 55

After development, liver cells stop cycling and stay in G₁.

Question 56

In animal cells, Cdk2/cyclin A act to drive cells through the restriction point in G₁.

Question 57

Rb is a member of the family of tumor suppressor genes.

Question 58

Rb is a tumor suppressor protein that acts by inhibiting phosphorylation of Cdk.

Question 59

ATM and ATR recognize damaged or unreplicated DNA and initiate signals that arrest cells at cell cycle checkpoints.

Question 60

ATM recognizes single-stranded DNA breaks and ATR recognizes double-stranded DNA breaks.

Question 61

Transcription ceases as chromosome condensation occurs.

Question 62

Re-formation of the nuclear envelope occurs as the result of cyclin B destruction, which allows phosphatases to dephosphorylate nuclear envelope lamins.

Question 63

A mutant cyclin B that is resistant to degradation by protease, but is otherwise active, would block the metaphase-to-anaphase transition.

Question 64

The metaphase-to-anaphase transition in animal cells is triggered by the breakdown of cyclin B.

Question 65

In what phase(s) of the cell cycle does growth typically occur?

Question 66

What does the spindle assembly checkpoint prevent?

Question 67

Identify the four different molecular mechanisms by which the activity of cyclin-dependent kinases is regulated after they are synthesized.

Question 68

To investigate the role of APC/C ubiquitin ligase in an experimental cell culture model, you are able to insert a plasmid gene encoding a mutant APC/C protein that is always active (i.e., cannot be inhibited). What would be the predicted outcome on the cells that received this mutant APC/C?

Question 69

How is DNA replication prevented from recurring in a single cell cycle?

Question 70

How is the anaphase-promoting complex/cyclosome (APC/C) activated?

Question 71

Dephosphorylation of proteins that were phosphorylated during prophase leads to what three telophase events?

Question 72

What determines the location of the contractile ring of filaments that mediate cytokinesis in an animal cell?

Question 73

Cytokinesis occurs in a plane that passes through which area of a cell?

Question 74

Interphase is defined as

A) the G₁ and G₂ phases.
B) the G₁, G₂, and S phases.
C) G₀, the quiescent phase.
D) M phase.

Question 75

The phase of the cell cycle that corresponds to the interval between mitosis and initiation of DNA replication is referred to as the

A) M phase.
B) S phase.
C) G₁ phase.
D) G₂ phase.

Question 76

You perform an experiment by incubating a radiolabeled nucleotide into the medium of a culture of cells. The cells that take up the radiolabel would be expected to be in what phase of the cell cycle?

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

Question 77

In which of the following cell types do G₁ and G₂ not take place?

A) Early embryonic cells
B) Budding yeast cells
C) Typical proliferating human cells
D) Skin fibroblasts

Question 78

DNA content can be found using a method of flow cytometry that can determine 2n or 4n states of cells based on cell counting and fluorescent labeling of DNA. Which of the following phases would be identified through flow cytometry as 2n?

A) G₁ phase only
B) S phase only
C) G₂ phase only
D) Both G₂ and M phases

Question 79

In the absence of growth factor, most animal cells will stop the cell cycle at a restriction point in what stage?

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

Question 80

In yeast, START triggers the progression from G₁ to S. Which of the following are involved in regulating START?

A) Nutrients
B) Mating factors
C) Cell size
D) All of the above