Test Bank for Essential Cell Biology
6th Edition By Bruce Alberts, Karen
Hopkin, Alexander Johnso
What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase
only?
(a) Cells would not be able to replicate their DNA.
(b) The mitotic spindle could not assemble.
(c) Cells would get larger and larger.
(d) The cells produced would get smaller and smaller. - ANSWER(d) The cells produced would get smaller
and smaller.
Which of the following events does not usually occur during interphase?
(a) Cells grow in size.
(b) The nuclear envelope breaks down.
(c) DNA is replicated.
(d) The centrosomes are duplicated. - ANSWER(b) The nuclear envelope breaks down.
In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly
replicated?
(a) at the transition between G1 and S
(b) when cells enter G0
(c) during M
(d) at the end of G2 - ANSWER(d) at the end of G2
Which of the following statements about the cell cycle is false?
,(a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic
cells.
(b) An unfavorable environment can cause cells to arrest in G1.
(c) A cell has more DNA during G2 than it did in G1.
(d) The cleavage divisions that occur in an early embryo have short G1 and G2 phases. - ANSWER(a)
Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.
Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required
for a checkpoint mechanism that operates in G2?
(a) The cell would be unable to enter M phase.
(b) The cell would be unable to enter G2.
(c) The cell would enter M phase under conditions when normal cells would not.
(d) The cell would pass through M phase more slowly than normal cells - ANSWER(c) The cell would
enter M phase under conditions when normal cells would not.
Progression through the cell cycle requires a cyclin to bind to a Cdk because _________.
(a) the cyclins are the molecules with the enzymatic activity in the complex.
(b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity.
(c) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle.
(d) without cyclin binding, a cell-cycle checkpoint will be activated. - ANSWER(b) the binding of a cyclin
to Cdk is required for Cdk enzymatic activity.
Levels of Cdk activity change during the cell cycle, in part because ________________.
(a) the Cdks phosphorylate each other.
(b) the Cdks activate the cyclins.
(c) Cdk degradation precedes entry into the next phase of the cell cycle.
(d) cyclin levels change during the cycle. - ANSWER(d) cyclin levels change during the cycle.
The concentration of mitotic cyclin (M cyclin) ________________.
(a) rises markedly during M phase.
,(b) is activated by phosphorylation.
(c) falls toward the end of M phase as a result of ubiquitylation and degradation.
(d) is highest in G1 phase. - ANSWER(c) falls toward the end of M phase as a result of ubiquitylation and
degradation.
You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase
at 37°C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced
and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-
sensitive mutations could not be responsible for the behavior of this strain of yeast?
(a) inactivation of a protein kinase that acts on the mitotic Cdk kinase
(b) inactivation of an enzyme that ubiquitylates M cyclin
(c) inactivation of a phosphatase that acts on the mitotic Cdk kinase
(d) a decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M
cyclin - ANSWER(b) inactivation of an enzyme that ubiquitylates M cyclin
You engineer yeast cells that express the M cyclin during S phase by replacing the promoter sequence of
the M cyclin gene with that of S cyclin. Keeping in mind that yeast cells have one common Cdk that binds
to all cyclins, which of the following outcomes is least likely during this experiment?
(a) There will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase.
(b) Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S
phase.
(c) G1 cyclins will be expressed during S phase.
(d) S-Cdk targets will be phosphorylated during S phase. - ANSWER(c) G1 cyclins will be expressed during
S phase.
Which of the following statements is false?
(a) Mitotic Cdk must be phosphorylated by an activating kinase (Cak) before it is active.
(b) Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive, even if it is
phosphorylated by the activating kinase.
(c) Active M-Cdk phosphorylates the activating phosphatase (Cdc25) in a positive feedback loop.
(d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be
active. - ANSWER(d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so
that M-Cdk will be active.
, MPF activity was discovered when cytoplasm from a Xenopus M-phase cell was injected into Xenopus
oocytes, inducing the oocytes to form a mitotic spindle. In a control experiment, Xenopus interphase
cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle. Which
of the following statements is not a legitimate conclusion from the control experiment?
(a) The piercing of the oocyte membrane by a needle is insufficient to cause mitotic spindle formation.
(b) An increased volume of cytoplasm is insufficient to cause mitotic spindle formation.
(c) Injection of extra RNA molecules is insufficient to cause mitotic spindle formation.
(d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation. -
ANSWER(d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation.
Which of the following is not good direct evidence that the cell-cycle control system is conserved
through billions of years of divergent evolution?
(a) A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the
cell cycle.
(b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in
humans.
(c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast.
(d) Yeast cells have only one Cdk, whereas humans have many Cdks. - ANSWER(d) Yeast cells have only
one Cdk, whereas humans have many Cdks.
Mitogens are _____.
(a) extracellular signals that stimulate cell division.
(b) transcription factors important for cyclin production.
(c) kinases that cause cells to grow in size.
(d) produced by mitotic cells to keep nearby neighboring cells from dividing. - ANSWER(a) extracellular
signals that stimulate cell division.
The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______.
(a) phosphorylating Cdk.
(b) marking cyclins for destruction by proteolysis.
(c) inhibiting cyclin transcription.
6th Edition By Bruce Alberts, Karen
Hopkin, Alexander Johnso
What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase
only?
(a) Cells would not be able to replicate their DNA.
(b) The mitotic spindle could not assemble.
(c) Cells would get larger and larger.
(d) The cells produced would get smaller and smaller. - ANSWER(d) The cells produced would get smaller
and smaller.
Which of the following events does not usually occur during interphase?
(a) Cells grow in size.
(b) The nuclear envelope breaks down.
(c) DNA is replicated.
(d) The centrosomes are duplicated. - ANSWER(b) The nuclear envelope breaks down.
In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly
replicated?
(a) at the transition between G1 and S
(b) when cells enter G0
(c) during M
(d) at the end of G2 - ANSWER(d) at the end of G2
Which of the following statements about the cell cycle is false?
,(a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic
cells.
(b) An unfavorable environment can cause cells to arrest in G1.
(c) A cell has more DNA during G2 than it did in G1.
(d) The cleavage divisions that occur in an early embryo have short G1 and G2 phases. - ANSWER(a)
Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eukaryotic cells.
Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required
for a checkpoint mechanism that operates in G2?
(a) The cell would be unable to enter M phase.
(b) The cell would be unable to enter G2.
(c) The cell would enter M phase under conditions when normal cells would not.
(d) The cell would pass through M phase more slowly than normal cells - ANSWER(c) The cell would
enter M phase under conditions when normal cells would not.
Progression through the cell cycle requires a cyclin to bind to a Cdk because _________.
(a) the cyclins are the molecules with the enzymatic activity in the complex.
(b) the binding of a cyclin to Cdk is required for Cdk enzymatic activity.
(c) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle.
(d) without cyclin binding, a cell-cycle checkpoint will be activated. - ANSWER(b) the binding of a cyclin
to Cdk is required for Cdk enzymatic activity.
Levels of Cdk activity change during the cell cycle, in part because ________________.
(a) the Cdks phosphorylate each other.
(b) the Cdks activate the cyclins.
(c) Cdk degradation precedes entry into the next phase of the cell cycle.
(d) cyclin levels change during the cycle. - ANSWER(d) cyclin levels change during the cycle.
The concentration of mitotic cyclin (M cyclin) ________________.
(a) rises markedly during M phase.
,(b) is activated by phosphorylation.
(c) falls toward the end of M phase as a result of ubiquitylation and degradation.
(d) is highest in G1 phase. - ANSWER(c) falls toward the end of M phase as a result of ubiquitylation and
degradation.
You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase
at 37°C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced
and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-
sensitive mutations could not be responsible for the behavior of this strain of yeast?
(a) inactivation of a protein kinase that acts on the mitotic Cdk kinase
(b) inactivation of an enzyme that ubiquitylates M cyclin
(c) inactivation of a phosphatase that acts on the mitotic Cdk kinase
(d) a decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M
cyclin - ANSWER(b) inactivation of an enzyme that ubiquitylates M cyclin
You engineer yeast cells that express the M cyclin during S phase by replacing the promoter sequence of
the M cyclin gene with that of S cyclin. Keeping in mind that yeast cells have one common Cdk that binds
to all cyclins, which of the following outcomes is least likely during this experiment?
(a) There will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase.
(b) Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S
phase.
(c) G1 cyclins will be expressed during S phase.
(d) S-Cdk targets will be phosphorylated during S phase. - ANSWER(c) G1 cyclins will be expressed during
S phase.
Which of the following statements is false?
(a) Mitotic Cdk must be phosphorylated by an activating kinase (Cak) before it is active.
(b) Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive, even if it is
phosphorylated by the activating kinase.
(c) Active M-Cdk phosphorylates the activating phosphatase (Cdc25) in a positive feedback loop.
(d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be
active. - ANSWER(d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so
that M-Cdk will be active.
, MPF activity was discovered when cytoplasm from a Xenopus M-phase cell was injected into Xenopus
oocytes, inducing the oocytes to form a mitotic spindle. In a control experiment, Xenopus interphase
cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle. Which
of the following statements is not a legitimate conclusion from the control experiment?
(a) The piercing of the oocyte membrane by a needle is insufficient to cause mitotic spindle formation.
(b) An increased volume of cytoplasm is insufficient to cause mitotic spindle formation.
(c) Injection of extra RNA molecules is insufficient to cause mitotic spindle formation.
(d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation. -
ANSWER(d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation.
Which of the following is not good direct evidence that the cell-cycle control system is conserved
through billions of years of divergent evolution?
(a) A yeast cell lacking a Cdk function can use the human Cdk to substitute for its missing Cdk during the
cell cycle.
(b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cyclins in
humans.
(c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast.
(d) Yeast cells have only one Cdk, whereas humans have many Cdks. - ANSWER(d) Yeast cells have only
one Cdk, whereas humans have many Cdks.
Mitogens are _____.
(a) extracellular signals that stimulate cell division.
(b) transcription factors important for cyclin production.
(c) kinases that cause cells to grow in size.
(d) produced by mitotic cells to keep nearby neighboring cells from dividing. - ANSWER(a) extracellular
signals that stimulate cell division.
The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by ______.
(a) phosphorylating Cdk.
(b) marking cyclins for destruction by proteolysis.
(c) inhibiting cyclin transcription.
