Molecular Cell Biology - Problem Drill 21: Cell Cycle and Cell Death
Question No. 1 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
1. Which of the following statements about the cell cycle is correct?
Question #1
(A) The Cell Cycle contains 3 distinct phases: (1) S Phase, (2) G2 and (3) M
Phase.
(B) The Cell Cycle contains 4 distinct phases: (1) G1, (2) S Phase, (3) G2 and (4)
M Phase.
(C) Cell-Cycle Control System uses lipids, which utilize key checkpoints to
control cell-cycle progression.
(D) Cell-Cycle Control System uses carbohydrates, which utilize key checkpoints
to control cell-cycle progression.
A. Incorrect!
The Cell Cycle contains 4 distinct phases: (1) G1, (2) S Phase, (3) G2 and (4) M
Phase.
B. Correct!
The Cell Cycle contains 4 distinct phases: (1) G1, (2) S Phase, (3) G2 and (4) M
Phase.
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Choice
C. Incorrect!
Cell-Cycle Control System uses a regulatory set of proteins, which utilize key
checkpoints to control cell-cycle progression.
D. Incorrect!
Cell-Cycle Control System uses a regulatory set of proteins, which utilize key
checkpoints to control cell-cycle progression.
The cell cycle is required for cell division and it is highly regulated to ensure
accurate cell replication.
The Cell Cycle: Facilitates Cell Reproduction: Through Duplication of Cell Contents
and Organelles. Contains 4 Distinct Phases: (1) G1, (2) S Phase, (3) G2 and (4) M
Phase. Cell-Cycle Control System: A Regulatory set of Proteins which Utilize Key
Checkpoints To control Cell-Cycle Progression.
Solution
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Question No. 2 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
2. Gap 1(G1) Phase ___________.
Question #2
(A) A cell enters G0 when the signal to divide is turned on; some cells exist in a
G0 state for days, weeks or years.
(B) G1 is when the cell monitors its environment and position.
(C) The duration of the G1 phase is from the completion of mitosis to the
beginning of DNA replication during S phase, also known as interphase.
(D) The duration of the G1 phase is from the completion of S Phase to the
beginning of Mitosis also known as interphase.
A. Incorrect!
A cell enters G0 when the signal to divide is turned off; some cells exist in a G0
state for days, weeks or years.
B. Incorrect!
G1 is when the cell monitors its environment and size. During this time the cell
grows.
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Choice
C. Correct!
The duration of the G1 phase is from the completion of mitosis to the beginning of
DNA replication during S phase, also known as interphase.
D. Incorrect!
The duration of the G1 phase is from the completion of mitosis to the beginning of
DNA replication during S phase, also known as interphase.
G1: The duration of the G1 phase is from the completion of mitosis to the beginning
of DNA replication during S phase, also known as interphase. Within the G1 phase is
a resting state known as G0. A cell enters G0 when the signal to divide is turned off;
some cells exist in a G0 state for days, weeks or years.
In cells that are actively cycling through the cell cycle, G1 is when the cell monitors
its environment and size. During this time the cell grows.
Solution
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Question No. 3 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
3. Which of the following statements about S Phase is correct?
Question #3
(A) In order for a cell to divide successfully, it must copy its DNA to be able to
supply 2 daughter cells. During S phase, a cell must copy most of its DNA.
(B) In order for a cell to divide successfully, it must copy its entire DNA to be
able to supply 2 daughter cells. During S phase, (synthesis phase) a cell
must copy its chromosome and the entire DNA it contains.
(C) S phase lasts approximately 8 days in normal eukaryotic cells.
(D) During S Phase, DNA must be made severed for replication and returned to
its resting state.
A. Incorrect!
In order for a cell to divide successfully, it must copy its entire DNA to be able to
supply 2 daughter cells. During S phase, (synthesis phase) a cell must copy its
chromosome and the entire DNA it contains.
B. Correct!
In order for a cell to divide successfully, it must copy its entire DNA to be able to
supply 2 daughter cells. During S phase, (synthesis phase) a cell must copy its
chromosome and the entire DNA it contains.
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Choice
C. Incorrect!
S phase lasts approximately 8 hours in normal eukaryotic cells.
D. Incorrect!
During this time, DNA must be made accessible for replication and returned to its
resting state.
In order for a cell to divide successfully, it must copy its entire DNA to be able to
supply 2 daughter cells. During S phase, (synthesis phase) a cell must copy its
chromosome and the entire DNA it contains.
S phase lasts approximately 8 hours in normal eukaryotic cells. During this time,
DNA must be made accessible for replication and returned to its resting state.
Solution
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Question No. 4 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
4. Which of the following statements about replication forks is correct?
Question #4
(A) During DNA replication, a Replication fork is formed and this is where the
existing DNA serves as a template to copy and produce a complete second
set.
(B) There are many replication forks initiated one after the other, they do not
exist at the same time.
(C) A single replication forks must complete the replication of approximately 3.5
billion nucleotides.
(D) In order for DNA replication to begin, the DNA itself must be unwound and
accessible. DNA polymerase proceeds the replication sites and performs this
function.
A. Correct!
During DNA replication, a Replication fork is formed and this is where the existing
DNA serves as a template to copy and produce a complete second set.
B. Incorrect!
There are many replication forks initiated simultaneously throughout the
chromosome, to complete the replication of approximately 3.5 billion nucleotides.
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Choice
C. Incorrect!
There are many replication forks initiated simultaneously throughout the
chromosome, to complete the replication of approximately 3.5 billion nucleotides.
D. Incorrect!
In order for DNA replication to begin, the DNA itself must be unwound and
accessible. DNA Helicase preceeds the replication sites and performs this function.
Solution
During DNA replication, a Replication fork is formed and this is where the existing
DNA serves as a template to copy and produce a complete second set. There are
many replication forks initiated simultaneously throughout the chromosome, to
complete the replication of approximately 3.5 billion nucleotides.
In order for DNA replication to begin, the DNA itself must be unwound and
accessible. DNA Helicase preceeds the replication sites and performs this function.
RNA primers serve as the templates from which DNA polymerases can start joining
pairs of nucleotides together.
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Question No. 5 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
5. Which of the following statements about Gap 2 (G2) is correct?
Question #5
(A) The G2 phase is usually the longest phase of the cell cycle.
(B) The G2 phase is usually the longest phase of the cell cycle. The size of the
cell is verified prior to the cell entering Mitosis.
(C) Gap 2 (G2): is the interphase between the end of S phase and beginning of
Mitosis.
(D) Gap 2 (G2): is the interphase between the end of Mitosis and the beginning
of S phase.
A. Incorrect!
The G2 phase is usually the shortest phase of the cell cycle.
B. Incorrect!
The G2 phase is usually the shortest phase of the cell cycle. The fidelity of the
copied DNA is verified prior to the cell entering Mitosis.
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Choice
C. Correct!
Gap 2 (G2): is the interphase between the end of S phase and beginning of Mitosis.
D. Incorrect!
Gap 2 (G2): is the interphase between the end of S phase and beginning of Mitosis.
Gap 2 (G2): is the interphase between the end of S phase and beginning of Mitosis.
During G2, the cell verifies the accuracy of the DNA replication that took place
during S phase.
The G2 phase is usually the shortest phase of the cell cycle. The fidelity of the
copied DNA is verified prior to the cell entering Mitosis.
Solution
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Question No. 6 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
6. Which of the following statements about mitosis is correct?
Question #6
(A) Mitosis involves the dividing of the nucleus and the surrounding cell. Mitosis
occurs directly after G1 phase.
(B) During mitosis, the parent DNA and copied DNA must be combined.
(C) During mitosis, the parent DNA and copied DNA must be separated.
(D) Following mitosis the cytosol and cell membrane are combined.
A. Incorrect!
Mitosis involves the dividing of the nucleus and the surrounding cell. Mitosis occurs
after the successful replication of the cell’s DNA.
B. Incorrect!
During mitosis, the parent DNA and copied DNA must be separated.
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Choice
C. Correct!
During mitosis, the parent DNA and copied DNA must be separated.
D. Incorrect!
Following mitosis the cytosol and cell membrane divide during cytokinesis.
Mitosis involves the dividing of the nucleus and the surrounding cell. Mitosis occurs
after the successful replication of the cell’s DNA.
During mitosis, the parent DNA and copied DNA must be separated. Following this
event, the cytosol and cell membrane divide during cytokinesis.
Solution
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Question No. 7 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
7. Which of the following statements about prometaphase, in mitosis is correct?
Question #7
(A) Prometaphase is one of 4 events that occur during mitosis.
(B) Prometaphase – begins with the breakdown of the nuclear envelope.
(C) Prometaphase – begins with the breakdown of the mitotic spindle.
(D) During prometaphase chromosomes unwind their DNA for replication.
A. Incorrect!
Mitosis can be divides into 5 distinct events: (1) Prophase, (2) Prometaphase, (3)
Metaphase, (4) Anaphase and (5) Telophase.
B. Correct!
Prometaphase – begins with the breakdown of the nuclear envelope.
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Choice
C. Incorrect!
Prometaphase – begins with the breakdown of the nuclear envelope.
D. Incorrect!
During prometaphase chromosomes attach to spindle microtubules at their
kinetochore.
Solution
Mitosis can be divides into 5 distinct events: (1) Prophase, (2) Prometaphase, (3)
Metaphase, (4) Anaphase and (5) Telophase.
(1) Prophase – the normally loosely packed chromatin is condensed into the
chromosome. The two centrosomes (Mitotic Spindle) begin to extend microtubules
in preparation for attaching to the chromosomes.
(2) Prometaphase – begins with the breakdown of the nuclear envelope.
Chromosomes attach to spindle microtubules at their kinetochore.
(3) Metaphase – the chromosomes are aligned at the center of the cell. Each of the
sister chromatids (2 per chromosome) are attached to opposite poles of the mitotic
spindle.
(4) Anaphase – the sister chromatids are separated and pulled towards the spindle
they are connected to.
(5) Anaphase – the sister chromatids arrive at the spindles and decondense; the
microtubules dissassemble. A nuclear envelope reassembles around each of the 2
separated sets of chromosomes. The cell is now ready for cytokineses (division of
the cytoplasm).
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Question No. 8 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
8. Which of the following statements about cell cycle checkpoints is correct?
Question #8
(A) During S phase, the DNA is replicated; if there were errors detected in the
replicated DNA, progression through this checkpoint into G2 would be
delayed/inhibited.
(B) During G1 phase, the DNA is replicated; if there were errors detected in the
replicated DNA, progression through this checkpoint into mitosis would be
delayed/inhibited.
(C) Prior to a cell entering S phase, both the cell size and integrity of the DNA
that was replicated during G1, are checked to ensure conditions are ready to
replicate the DNA.
(D) During mitosis, there is a checkpoint prior to the cell entering S phase and
dividing into 2 daughter cells.
A. Correct!
During S phase, the DNA is replicated; if there were errors detected in the
replicated DNA, progression through this checkpoint into G2 would be
delayed/inhibited.
B. Incorrect!
During S phase, the DNA is replicated; if there were errors detected in the
replicated DNA, progression through this checkpoint into G2 would be
delayed/inhibited.
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Choice
C. Incorrect!
Prior to a cell entering S phase, both the cell size and environment are checked to
ensure conditions are ready to replicate the DNA. Damaged DNA or a cell that is too
small can block the passage through this checkpoint.
D. Incorrect!
During mitosis, there is a checkpoint prior to the cell entering the cytokinesis phase
and dividing into 2 daughter cells.
Solution
The cell cycle is controlled largely by a central cell-cycle control system, made up of
checkpoints. Each major step must be completed and accuracy confirmed before
the cell moves into the next phase of the cell cycle. Each checkpoint involves a
series of steps that take place prior to progression. During S phase, the DNA is
replicated; if there were errors detected in the replicated DNA, progression through
this checkpoint into G2 would be delayed/inhibited.
Prior to a cell entering S phase, both the cell size and environment are checked to
ensure conditions are ready to replicate the DNA. Damaged DNA or a cell that is to
small can block the passage through this checkpoint. During mitosis, there is a
checkpoint prior to the cell entering the cytokinesis phase and dividing into 2
daughter cells. During this checkpoint, the chromosomes are confirmed to be
aligned on the spindles, to allow proper separation into 2 separate future nuclei.
Prior to a cell entering mitosis, there is a checkpoint to ensure that: the entire DNA
was replicated correctly, the environment is favorable and the cell is big enough for
cell division.
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Question No. 9 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
9. Which of the following statements about programmed cell death (apoptosis) is
correct?
Question #9
(A) Programmed cell death is a mechanism used by the body to remove
unwanted cells as part of normal development, injury and disease.
(B) A family of proteolytic enzymes called actinases mediates programmed cell
death.
(C) A family of lipids called caspases mediates programmed cell death.
(D) Apoptotic bodies degrade and leak cellular content into the interstitial space,
triggering the inflammation cascade.
A. Correct!
Programmed cell death is a mechanism used by the body to remove unwanted cells
as part of normal development, injury and disease.
B. Incorrect!
A family of proteolytic enzymes called caspases mediates programmed cell death.
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Solution
C. Incorrect!
A family of proteolytic enzymes called caspases mediates programmed cell death.
D. Incorrect!
Phagocytes ingest Apoptotic bodies and because the cell content did not leak into
the interstitial space, there is no inflammation cascade.
Programmed cell death is a mechanism used by the body to remove unwanted cells
as part of normal development, injury and disease. It is the deliberate suicide of a
cell that is highly regulated and quite different from necrosis, which includes
inflammation and accidental cell death. A family of proteolytic enzymes called
caspases mediates programmed cell death. These caspases are stored in cells as
inactive pre-caspases. Once activated, these enzymes cleave target proteins in the
nucleus and elsewhere in the cell, setting in motion this process. Cells can be
triggered into apoptosis by signals during the cell cycle, such as improperly
replicated DNA, etc. Once the cell begins this process, the cell itself shrinks in size
and the chromatin condenses. Next, the nuclear envelope breaks down, in part, due
to caspase cleavage of nuclear lamins. Also, the DNA itself is severed into small
pieces during this step. Then, the cell breaks into small pieces called apoptotic
bodies. These pieces are surrounded by plasma membrane, keeping the cellular
contents inside. Finally, phagocytes ingest the apoptotic bodies and because the
cell content did not leak into the interstitial space, there is no inflammation
cascade.
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Question No. 10 of 10
Instruction: (1) Read the problem statement and answer choices carefully (2) Work the problems
on paper as needed (3) Pick the answer (4) Go back to review the core concept tutorial as needed.
10. Which of the following statements about the extracellular control of apoptosis is
correct?
Question #10
(A) Mitogens and growth factors stimulate apoptosis.
(B) Mitogens and growth factors stimulate cell growth and division and,
therefore, stimulate cell cycle progression; apoptosis is not activated unless
there is abnormal DNA replication.
(C) Transforming growth factor β (TGF- β) does not stimulate apoptosis.
(D) Cells have unique death signals, or receptors, that are used to trigger
apoptosis. Examples include myosin and nerve growth factor.
A. Incorrect!
Mitogens and growth factors stimulate cell growth and division and, therefore,
stimulate cell cycle progression; apoptosis is not activated unless there is abnormal
DNA replication.
B. Correct!
Mitogens and growth factors stimulate cell growth and division and, therefore,
stimulate cell cycle progression; apoptosis is not activated unless there is abnormal
DNA replication.
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Choice
C. Incorrect!
Extracellular signals can trigger apoptosis in cells; one example is Transforming
growth factor β (TGF- β). TGF- β has a role in cell proliferation, embryonic
development and regulation of the immune system.
D. Incorrect!
Cells have unique death signals, or receptors, that are used to trigger apoptosis.
Examples include Fas ligand (FasL) and Tumor necrosis factor (TNF).
Solution
Mitogens and growth factors stimulate cell growth and division and, therefore,
stimulate cell cycle progression; apoptosis is not activated unless there is abnormal
DNA replication. Survival factors are a group of proteins used by cells. Survival
factors, such as neurotrophins (Nerve Growth Factor, Brain-Derived Neurotrophic
Factor), maintain cell survival in part by suppressing apoptosis. Extracellular signals
can trigger apoptosis in cells; one example is Transforming growth factor β (TGFβ). TGF- β has a role in cell proliferation, embryonic development and regulation of
the immune system. TGF- β binds to cell-surface receptors and activates the
caspase cascade of events, leading to apoptosis. Cells have unique death signals, or
receptors, that are used to trigger apoptosis. Examples include Fas ligand (FasL)
and Tumor necrosis factor (TNF). When these molecules bind to their specific
receptor, they initiate the death receptor-signaling pathway. An example of when
FasL is utilized is when cytotoxic T-cells kill target cells. By having the FasL
molecules expressed on the surface of the cells, they can induce apoptosis in the
target by engaging the Fas receptor on the target cell.
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