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What phase follows mitosis in the cell cycle? A) S Phase B) G1 Phase C) G2 Phase D) M Phase E) G0 Phase
B) G1 Phase Explanation: After mitosis, the cell enters the G1 phase, which is the interval between mitosis and the initiation of DNA replication.
During which phase does DNA replication occur? A) G1 Phase B) G2 Phase C) M Phase D) S Phase E) G0 Phase
D) S Phase Explanation: The S phase is specifically designated for DNA replication, where the genetic material is duplicated in preparation for cell division.
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p.1
G1 Phase Characteristics

What phase follows mitosis in the cell cycle?
A) S Phase
B) G1 Phase
C) G2 Phase
D) M Phase
E) G0 Phase

B) G1 Phase
Explanation: After mitosis, the cell enters the G1 phase, which is the interval between mitosis and the initiation of DNA replication.

p.1
S Phase and DNA Replication

During which phase does DNA replication occur?
A) G1 Phase
B) G2 Phase
C) M Phase
D) S Phase
E) G0 Phase

D) S Phase
Explanation: The S phase is specifically designated for DNA replication, where the genetic material is duplicated in preparation for cell division.

p.1
G1 Phase Characteristics

How long does the G1 phase typically last in a rapidly proliferating human cell?
A) 4 hours
B) 8 hours
C) 11 hours
D) 1 hour
E) 24 hours

C) 11 hours
Explanation: In a typical rapidly proliferating human cell, the G1 phase lasts about 11 hours, which is part of a total cell cycle time of 24 hours.

p.1
M Phase and Cytokinesis

What is the duration of the M phase in a rapidly proliferating human cell?
A) 4 hours
B) 1 hour
C) 8 hours
D) 11 hours
E) 30 minutes

B) 1 hour
Explanation: The M phase, which includes mitosis and cytokinesis, lasts about 1 hour in a rapidly proliferating human cell.

p.1
Quiescent Stage (G0) in Cell Cycle

What happens during the G0 phase?
A) Cells replicate their DNA
B) Cells cease division but remain metabolically active
C) Cells grow rapidly
D) Cells undergo mitosis
E) Cells enter apoptosis

B) Cells cease division but remain metabolically active
Explanation: In the G0 phase, cells exit the cell cycle and remain metabolically active without dividing unless stimulated by extracellular signals.

p.1
Cell Cycle Regulation by Extracellular Signals

What is the commitment point in the G1 phase known as?
A) Start
B) G0
C) M Phase
D) S Phase
E) G2 Phase

A) Start
Explanation: The commitment point near the end of G1 is referred to as Start in yeasts or the restriction point in mammalian cells, marking the point of no return for DNA replication.

p.1
Differences in Cell Cycles of Yeasts and Animal Cells

How long can budding yeasts complete the cell cycle?
A) 24 hours
B) 90 minutes
C) 30 minutes
D) 4 hours
E) 1 hour

B) 90 minutes
Explanation: Budding yeasts can progress through all four stages of the cell cycle in about 90 minutes, demonstrating a much faster cycle compared to human cells.

p.1
Differences in Cell Cycles of Yeasts and Animal Cells

What characterizes early embryonic cell cycles?
A) Long G1 and G2 phases
B) Rapid division without growth
C) Extensive DNA replication
D) No mitosis
E) Slow cell division

B) Rapid division without growth
Explanation: Early embryonic cell cycles are characterized by rapid division of the egg cytoplasm into smaller cells without significant growth, with very short S phases alternating with M phases.

p.2
Checkpoints in Cell Cycle Control

What is the START regulatory point in the yeast cell cycle?
A) A point where cells enter G2 phase
B) A decision point for nutrient availability
C) A phase where cells grow significantly
D) A checkpoint before mitosis
E) A phase that occurs after S phase

B) A decision point for nutrient availability
Explanation: START is a major regulatory point in the yeast cell cycle that determines whether sufficient nutrients are available to support progression to S phase, making it a critical decision point.

p.10
Checkpoints in Cell Cycle Control

What happens if the M-phase trigger is activated before DNA replication is complete?
A) The cell enters a normal mitosis
B) The cell undergoes apoptosis
C) The cell enters a suicidal mitosis
D) The cell remains in interphase
E) The cell divides normally

C) The cell enters a suicidal mitosis
Explanation: If the M-phase trigger is activated before DNA replication is complete, the cell enters a suicidal mitosis with partially replicated chromosomes, which is a critical failure in cell cycle regulation.

p.2
G1 Phase Characteristics

How does cell size affect the yeast cell cycle?
A) Smaller cells divide faster than larger cells
B) Larger cells cannot divide
C) Cell size must be monitored to coordinate growth and division
D) Cell size has no impact on the cycle
E) Smaller cells always enter S phase first

C) Cell size must be monitored to coordinate growth and division
Explanation: In budding yeasts, cell size is crucial for coordinating growth with DNA replication and cell division, as smaller daughter cells must grow more than larger mother cells before dividing again.

p.5
Role of Cyclins and Cdks

What is the primary advantage of using yeast to study mutations that inactivate a gene?
A) Yeast have multiple gene copies
B) Yeast are easy to grow in large quantities
C) Yeast can be used to isolate mutations without a second gene copy
D) Yeast have complex cell cycles
E) Yeast are resistant to environmental changes

C) Yeast can be used to isolate mutations without a second gene copy
Explanation: Using yeast allows researchers to isolate and study mutations that inactivate a gene without the complication of having a second gene copy in the cell, making it easier to analyze the effects of specific mutations.

p.11
G1 Phase Characteristics

During the early cleavages of the embryo, what is the relationship between DNA quantity and cytoplasm?
A) DNA quantity is high compared to cytoplasm
B) DNA quantity is irrelevant to cytoplasm
C) DNA quantity is too tiny in relation to cytoplasm
D) Cytoplasm is more important than DNA
E) DNA quantity is equal to cytoplasm

C) DNA quantity is too tiny in relation to cytoplasm
Explanation: In early embryonic cleavages, the quantity of DNA is too small compared to the cytoplasm, preventing DNA-dependent signals from affecting the control system.

p.9
M Phase and Cytokinesis

What happens when a mitotic mammalian cell fuses with an interphase mammalian cell?
A) The interphase nucleus remains unchanged
B) The interphase nucleus is driven into a mitotic state
C) The mitotic cell loses its chromosomes
D) Both cells die immediately
E) The mitotic cell becomes interphase

B) The interphase nucleus is driven into a mitotic state
Explanation: The fusion of a mitotic mammalian cell with an interphase mammalian cell results in the interphase nucleus being driven directly into a mitotic state, causing chromosome condensation regardless of their replication state.

p.7
Differences in Cell Cycles of Yeasts and Animal Cells

What is a key difference between the early embryonic cell cycle and the standard cell cycle?
A) The presence of G1 and G2 phases
B) The occurrence of growth before division
C) The speed of cell division
D) The requirement for nutrient availability
E) The duration of interphase

C) The speed of cell division
Explanation: The early embryonic cell cycle occurs without growth and at extraordinary speed, contrasting with the standard cell cycle, which involves growth and is prolonged.

p.10
M Phase and Cytokinesis

What phenomenon occurs in the cortical cytoplasm of the non-nucleated Xenopus cell?
A) Continuous growth
B) Contraction and stiffening
C) Cell division
D) DNA replication
E) Protein synthesis

B) Contraction and stiffening
Explanation: The non-nucleated Xenopus cell exhibits contraction and stiffening of the cortical cytoplasm, which occurs in synchrony with the cleavage divisions of the nucleated half-egg.

p.6
Role of Cyclins and Cdks

What is the role of the cdc2 gene product in cell division?
A) It prevents mitosis from occurring
B) It drives the cell into mitosis
C) It regulates the cell's size
D) It initiates DNA replication
E) It repairs damaged DNA

B) It drives the cell into mitosis
Explanation: The cdc2 gene product is essential for driving the cell into mitosis. When it is defective, mitosis fails to occur, indicating its critical role in cell division.

p.2
Differences in Cell Cycles of Yeasts and Animal Cells

What characterizes early embryonic cell cycles?
A) Cells grow significantly during these cycles
B) They consist of long G1 and G2 phases
C) They rapidly divide without growth
D) They only occur in adult cells
E) They include extensive DNA repair phases

C) They rapidly divide without growth
Explanation: Early embryonic cell cycles are characterized by rapid division of the cytoplasm without growth, lacking G1 and G2 phases, and consisting only of short S phases alternating with M phases.

p.9
S Phase and DNA Replication

What appearance do chromosomes adopt in the S phase of the PtK cell?
A) Condensed and double
B) Single chromatids
C) Pulverized
D) Unreplicated
E) Fragmented

C) Pulverized
Explanation: During the S phase, the chromatin of the PtK cell adopts a 'pulverized' appearance, reflecting the ongoing DNA replication process.

p.7
Role of Cyclins and Cdks

What is MPF, and what role does it play in the cell cycle?
A) A type of DNA
B) A cytoplasmic regulator
C) A growth factor
D) A type of RNA
E) A cell membrane component

B) A cytoplasmic regulator
Explanation: MPF (Maturation Promoting Factor) is identified as a cytoplasmic regulator that plays a crucial role in controlling the cell cycle, particularly during mitosis.

p.13
Phases of the Cell Cycle

What is the primary function of the cell cycle?
A) To produce energy
B) To duplicate contents and divide the cell
C) To transport nutrients
D) To synthesize proteins
E) To eliminate waste

B) To duplicate contents and divide the cell
Explanation: The cell cycle is defined as the orderly sequence of events in which a cell duplicates its contents and divides into two, serving as the essential mechanism for reproduction in living organisms.

p.2
Cell Cycle Regulation by Extracellular Signals

What happens to yeast cells when faced with nutrient shortages at START?
A) They proceed to S phase
B) They undergo apoptosis
C) They arrest their cell cycle
D) They double their size
E) They enter mitosis

C) They arrest their cell cycle
Explanation: When yeast cells encounter nutrient shortages at START, they arrest their cell cycle and enter a resting state instead of proceeding to S phase, highlighting the importance of nutrient availability.

p.5
Checkpoints in Cell Cycle Control

In budding yeast, which checkpoint is considered the most important for size regulation?
A) G2 checkpoint
B) M phase checkpoint
C) G1 checkpoint (Start)
D) S phase checkpoint
E) Cytokinesis checkpoint

C) G1 checkpoint (Start)
Explanation: In budding yeast, the G1 checkpoint, known as Start, is the most critical size checkpoint, determining whether the cell can proceed to the next phase of the cell cycle based on its size.

p.3
Cell Cycle Regulation by Extracellular Signals

What is the key regulatory point in the cell cycle of budding yeast called?
A) G2 Phase
B) START
C) S Phase
D) Restriction Point
E) G0 Phase

B) START
Explanation: The cell cycle of Saccharomyces cerevisiae is primarily regulated at a point in late G1 called START, which is crucial for controlling the progression of the cell cycle.

p.4
Differences in Cell Cycles of Yeasts and Animal Cells

In which phase is the cell cycle primarily regulated in fission yeast (Schizosaccharomyces pombe)?
A) G1
B) S
C) G2
D) M
E) G0

C) G2
Explanation: The cell cycle of fission yeast is primarily regulated at the transition from G2 to M phase, where cell size and nutrient availability are monitored, contrasting with other organisms where G1 is the main regulatory phase.

p.12
Role of Cyclins and Cdks

Which class of cyclins is responsible for committing the cell to DNA replication?
A) M-cyclins
B) G1-cyclins
C) S-cyclins
D) G1/S-cyclins
E) G2-cyclins

D) G1/S-cyclins
Explanation: G1/S-cyclins bind Cdks at the end of the G1 phase, committing the cell to proceed with DNA replication.

p.9
G1 Phase Characteristics

What phase was the PtK cell in when its chromosomes were still single chromatids?
A) G2 phase
B) S phase
C) G1 phase
D) M phase
E) G0 phase

C) G1 phase
Explanation: In the experiment, when the PtK cell was in G1 phase, its prematurely condensed chromosomes were still single chromatids, indicating that replication had not yet occurred.

p.6
Cell Cycle Regulation by Extracellular Signals

What happens when the cdc2 gene product is released from normal control?
A) Mitosis occurs at the correct time
B) Mitosis fails to occur
C) Mitosis occurs prematurely
D) The cell enters G1 phase
E) The cell undergoes apoptosis

C) Mitosis occurs prematurely
Explanation: When the cdc2 gene product is released from normal control, it leads to premature mitosis, which can disrupt normal cell cycle regulation.

p.11
M Phase and Cytokinesis

What happens if DNA replication is not complete before entering mitosis?
A) The cell divides normally
B) The cell is prevented from entering mitosis
C) The cell undergoes apoptosis
D) The cell continues to replicate DNA
E) The cell doubles its DNA content

B) The cell is prevented from entering mitosis
Explanation: The control system prevents entry into mitosis if DNA replication is incomplete, ensuring that the cell cycle progresses correctly.

p.8
Role of Cyclins and Cdks

What is the Cdk subunit of MPF named after?
A) A plant species
B) A gene in fission yeast
C) A mammalian cell type
D) A type of bacteria
E) A fruit fly gene

B) A gene in fission yeast
Explanation: The Cdk subunit of MPF is named Cdc2 after the gene in fission yeast that encodes it, highlighting its origin and significance in cell cycle regulation.

p.3
G1 Phase Characteristics

What happens to the daughter cell formed from the bud in budding yeast?
A) It is larger than the mother cell
B) It is the same size as the mother cell
C) It is smaller than the mother cell
D) It does not grow
E) It divides immediately

C) It is smaller than the mother cell
Explanation: The daughter cell formed from the bud is smaller than the mother cell, which means it requires more time to grow during the G1 phase of the next cell cycle.

p.8
Role of Cyclins and Cdks

What is the relationship between maturation promoting factor and M-phase-promoting factor?
A) They are completely different substances
B) They are two names for the same substance
C) M-phase-promoting factor is a precursor to maturation promoting factor
D) They function in different types of cells
E) They are both produced in the nucleus

B) They are two names for the same substance
Explanation: Maturation promoting factor and M-phase-promoting factor refer to the same substance, MPF, which plays a crucial role in driving cells into mitosis and maturation.

p.1
Differences in Cell Cycles of Yeasts and Animal Cells

Which type of cells in adult animals typically cease division?
A) Skin fibroblasts
B) Nerve cells
C) Liver cells
D) Muscle cells
E) Blood cells

B) Nerve cells
Explanation: Nerve cells in adult animals typically cease division altogether, contrasting with other cells that may divide occasionally.

p.12
Role of Cyclins and Cdks

Which of the following is NOT a class of cyclins mentioned in the text?
A) G1-cyclins
B) S-cyclins
C) M-cyclins
D) G2-cyclins
E) G1/S-cyclins

D) G2-cyclins
Explanation: The text mentions G1-cyclins, S-cyclins, M-cyclins, and G1/S-cyclins, but does not refer to G2-cyclins as a distinct class.

p.10
Role of Cyclins and Cdks

What does the oscillation of the non-nucleated half of the Xenopus egg reflect?
A) Changes in temperature
B) Oscillations of MPF activity
C) Variations in nutrient levels
D) Cell membrane integrity
E) DNA replication rates

B) Oscillations of MPF activity
Explanation: The visible oscillations in the non-nucleated half of the Xenopus egg reflect oscillations of MPF (M-phase promoting factor) activity, indicating a link between cytoplasmic changes and cell cycle regulation.

p.10
Checkpoints in Cell Cycle Control

What protects the cell from entering mitosis with incompletely replicated DNA?
A) Nutrient stockpiles
B) Feedback signal from incompletely replicated DNA
C) Cyclin levels
D) MPF activity
E) External signals

B) Feedback signal from incompletely replicated DNA
Explanation: A feedback signal from incompletely replicated DNA protects the cell from entering mitosis prematurely, ensuring that DNA replication is complete before cell division occurs.

p.5
Cell Cycle Regulation by Extracellular Signals

What type of mutation is characterized by cells dividing at a smaller size than normal?
A) cdc mutation
B) wee mutation
C) temperature-sensitive mutation
D) lethal mutation
E) conditional mutation

B) wee mutation
Explanation: The wee mutation, named from the Scottish word for small, refers to mutant cells that divide at a smaller size than normal, indicating a deficiency in a product that inhibits passage through a size checkpoint.

p.7
G1 Phase Characteristics

What happens to the size of cells during the rapid divisions in early embryonic development?
A) Cells grow larger with each division
B) Cells remain the same size
C) Cells get progressively smaller
D) Cells double in size
E) Cells become irregularly shaped

C) Cells get progressively smaller
Explanation: As the single giant cell cleaves rapidly without growth, the resulting cells become progressively smaller with each division until the tadpole begins feeding.

p.8
M Phase and Cytokinesis

What happens when M-phase cytoplasm from a mature unfertilized egg is injected into a G2-phase oocyte?
A) The oocyte remains in G2 phase
B) The oocyte undergoes apoptosis
C) The oocyte is driven into M phase
D) The oocyte divides immediately
E) The oocyte becomes a fertilized egg

C) The oocyte is driven into M phase
Explanation: Injecting M-phase cytoplasm into a G2-phase oocyte drives the recipient oocyte into M phase, completing its maturation, demonstrating the role of maturation promoting factor.

p.13
Phases of the Cell Cycle

How long does a typical eukaryotic cell cycle take?
A) 12 hours
B) 24 hours
C) 48 hours
D) 72 hours
E) 1 hour

B) 24 hours
Explanation: A typical eukaryotic cell cycle divides approximately every 24 hours, indicating the time frame for the processes of growth, DNA replication, and division.

p.4
Differences in Cell Cycles of Yeasts and Animal Cells

What distinguishes the cell cycle of budding yeast (Saccharomyces cerevisiae) from that of fission yeast?
A) Budding yeast has a normal G2 phase
B) Fission yeast divides by budding
C) Budding yeast does not have a normal G2 phase
D) Fission yeast has a longer G1 phase
E) Budding yeast does not undergo meiosis

C) Budding yeast does not have a normal G2 phase
Explanation: Unlike fission yeast, budding yeast does not have a normal G2 phase; instead, the microtubule-based spindle begins to form inside the nucleus early in the cycle during the S phase.

p.12
Role of Cyclins and Cdks

What is the role of cyclins in the cell cycle?
A) They are responsible for DNA repair
B) They regulate the activity of Cdks
C) They transport nutrients
D) They initiate apoptosis
E) They synthesize RNA

B) They regulate the activity of Cdks
Explanation: Cyclins are essential for the activation of Cdks, as they bind to these kinases and enable them to phosphorylate target proteins, thus regulating the cell cycle.

p.10
Cell Cycle Regulation by Extracellular Signals

During the early embryonic cycles of the developing frog, what is true about the control system?
A) It is highly variable
B) It operates with feedback signals
C) It goes through its cycle at a predictable rate
D) It is dependent on external signals
E) It is inactive

C) It goes through its cycle at a predictable rate
Explanation: In the early embryonic cycles of the developing frog, the control system operates at a predictable and invariant rate, allowing for timely progression through the cell cycle without feedback signals.

p.7
Role of Cyclins and Cdks

What are the two essential subunits of MPF?
A) Cyclin and Cdk
B) DNA and RNA
C) Protein and Lipid
D) ATP and GTP
E) Actin and Myosin

A) Cyclin and Cdk
Explanation: MPF consists of two essential subunits: a cyclin-dependent kinase (Cdk) called Cdc2 and a mitotic cyclin, which are crucial for its activity in regulating the cell cycle.

p.8
Cell Cycle Regulation by Extracellular Signals

What technique is crucial for identifying components of the cell-cycle control system?
A) Yeast fermentation
B) Xenopus oocyte assay technique
C) Bacterial transformation
D) Mammalian cell fusion
E) Plant tissue culture

B) Xenopus oocyte assay technique
Explanation: The Xenopus oocyte assay technique is essential for identifying components of the cell-cycle control system, as it allows for the study of cytoplasmic control mechanisms in defined stages of the cell cycle.

p.3
Cell Cycle Regulation by Extracellular Signals

What primarily regulates the passage of animal cells through the cell cycle?
A) Nutrient availability
B) Temperature
C) Extracellular growth factors
D) Cell size
E) Oxygen levels

C) Extracellular growth factors
Explanation: The passage of animal cells through the cell cycle is primarily regulated by extracellular growth factors that signal cell proliferation, unlike yeasts which are influenced by nutrient availability.

p.4
G2 Phase Functions

What is a primary example of cell cycle control in G2 in animals?
A) Skin fibroblasts
B) Oocytes
C) Muscle cells
D) Neurons
E) Stem cells

B) Oocytes
Explanation: In animals, oocytes serve as a primary example of cell cycle control in G2, where they can remain arrested for long periods until hormonal stimulation triggers their progression to the M phase.

p.12
Role of Cyclins and Cdks

What happens to the active site of a Cdk when it binds to a cyclin?
A) It becomes completely inactive
B) It is obscured by a protein
C) It is partially activated
D) It is destroyed
E) It remains unchanged

C) It is partially activated
Explanation: Binding of cyclin to Cdk causes a conformational change that partially activates the Cdk enzyme, allowing it to participate in cell cycle regulation.

p.11
S Phase and DNA Replication

What occurs as the egg undergoes the first 12 division cycles?
A) The quantity of cytoplasm decreases
B) The ratio of nuclear DNA to cytoplasm increases
C) The DNA quantity remains constant
D) The cell stops dividing
E) The cytoplasm becomes more dense

B) The ratio of nuclear DNA to cytoplasm increases
Explanation: Over the first 12 division cycles, the ratio of nuclear DNA to cytoplasm increases by more than 4000 times, allowing feedback controls of the cell cycle to begin operating.

p.11
Cell Cycle Regulation by Extracellular Signals

How do extracellular signals affect the cell cycle?
A) They have no effect on the cell cycle
B) They can only promote cell death
C) They regulate progression through checkpoints
D) They only affect the G2 phase
E) They speed up DNA replication

C) They regulate progression through checkpoints
Explanation: Extracellular signals can either promote or inhibit cell proliferation by regulating progression through checkpoints, particularly the G1 checkpoint.

p.8
M Phase and Cytokinesis

What is the initial name given to the activity identified in the egg cytoplasm that induces maturation?
A) M-phase-promoting factor
B) Cell division factor
C) Maturation promoting factor
D) Cytoplasmic control factor
E) Growth factor

C) Maturation promoting factor
Explanation: The activity that induces the maturation of an immature oocyte into a mature egg was initially called maturation promoting factor, which is later identified as MPF.

p.4
Differences in Cell Cycles of Yeasts and Animal Cells

How do diploid and haploid cells in yeast reproduce?
A) Only diploid cells can reproduce
B) Haploid cells can only undergo meiosis
C) Both can proliferate and mate
D) Only haploid cells can mate
E) Diploid cells cannot undergo meiosis

C) Both can proliferate and mate
Explanation: Both diploid and haploid cells in yeast can proliferate; diploid cells can undergo meiosis to form haploid cells, while haploid cells can mate with one another to form diploid cells.

p.9
Role of Cyclins and Cdks

What was discovered about MPF activity across different species?
A) It is only found in mammals
B) It is a universal feature of the eukaryotic cell cycle
C) It is absent in yeast
D) It varies significantly between species
E) It is only present in plants

B) It is a universal feature of the eukaryotic cell cycle
Explanation: MPF activity has been established as a universal feature of the eukaryotic cell cycle, detectable in all species from yeasts to mammals during mitosis.

p.11
Checkpoints in Cell Cycle Control

What is the role of checkpoints in the cell cycle?
A) To speed up the cell cycle
B) To allow for DNA replication only
C) To arrest the cell cycle at specific points
D) To prevent cell division entirely
E) To enhance cytoplasmic functions

C) To arrest the cell cycle at specific points
Explanation: Checkpoints are critical points in the cell cycle where the control system can halt progression if previous events, such as DNA replication, have not been completed.

p.13
Phases of the Cell Cycle

In unicellular species, what does each cell division produce?
A) A new organelle
B) A complete new organism
C) A group of cells
D) A larger cell
E) A dead cell

B) A complete new organism
Explanation: In unicellular species like bacteria and yeasts, each cell division results in the formation of a complete new organism, highlighting the simplicity of their reproductive process.

p.13
M Phase and Cytokinesis

What is the main event that occurs during mitosis?
A) DNA replication
B) Cell growth
C) Separation of daughter chromosomes
D) Nutrient absorption
E) Waste elimination

C) Separation of daughter chromosomes
Explanation: Mitosis is characterized by the separation of daughter chromosomes, which is a critical step in the cell division process.

p.12
Checkpoints in Cell Cycle Control

What is the significance of checkpoints in the cell cycle control system?
A) They allow for nutrient absorption
B) They prevent DNA replication
C) They ensure proper completion of cell-cycle events
D) They initiate apoptosis
E) They promote cell growth

C) They ensure proper completion of cell-cycle events
Explanation: Checkpoints in the cell cycle control system are critical for monitoring the completion of cell-cycle events and environmental signals, allowing the cycle to be arrested if necessary.

p.2
Cell Cycle Regulation by Extracellular Signals

What is the role of extracellular signals in the cell cycle?
A) They prevent all cell divisions
B) They regulate progression through the division cycle
C) They only affect DNA replication
D) They are irrelevant to cell cycle control
E) They only influence G2 phase

B) They regulate progression through the division cycle
Explanation: Extracellular signals from the environment play a crucial role in regulating the progression of cells through the division cycle, alongside internal signals that monitor and coordinate various processes.

p.7
M Phase and Cytokinesis

How long does each cycle of cell division in early embryonic development last?
A) 30 minutes
B) 15 minutes
C) 1 hour
D) 45 minutes
E) 10 minutes

B) 15 minutes
Explanation: Each cycle consists of a 15-minute M phase and a 15-minute interphase, indicating the rapid pace of cell division during early embryonic development.

p.5
Checkpoints in Cell Cycle Control

What is the function of the G2 checkpoint in the cell cycle?
A) To initiate DNA synthesis
B) To halt the cycle before mitosis
C) To allow cells to grow larger
D) To trigger cytokinesis
E) To prevent DNA replication

B) To halt the cycle before mitosis
Explanation: The G2 checkpoint serves to halt the cell cycle before mitosis, ensuring that the cell is adequately prepared to divide, which is crucial for maintaining proper cell function.

p.6
Role of Cyclins and Cdks

What is the primary role of cyclin in relation to Cdc2?
A) It inhibits Cdc2 activity
B) It activates Cdc2 when bound
C) It degrades Cdc2
D) It prevents the accumulation of MPF
E) It initiates DNA replication

B) It activates Cdc2 when bound
Explanation: Cyclin is necessary for the activation of Cdc2; when bound to cyclin B during interphase, Cdc2 becomes a substrate for phosphorylation, leading to MPF activation.

p.3
Cell Cycle Regulation by Extracellular Signals

What is the restriction point in animal cells analogous to in budding yeast?
A) G1 Phase
B) START
C) S Phase
D) G2 Phase
E) G0 Phase

B) START
Explanation: The restriction point in late G1 of animal cells functions analogously to START in yeasts, serving as a critical decision point for cell cycle progression.

p.13
Phases of the Cell Cycle

What percentage of the cell cycle is spent in interphase?
A) 5%
B) 25%
C) 50%
D) 95%
E) 100%

D) 95%
Explanation: Approximately 95% of the cell cycle is spent in interphase, which is the period between mitosis where the cell prepares for division.

p.1
G1 Phase Characteristics

What is the primary activity of cells during the G1 phase?
A) DNA replication
B) Cell division
C) Metabolic activity and growth
D) Protein synthesis
E) Apoptosis

C) Metabolic activity and growth
Explanation: During the G1 phase, cells are metabolically active and continuously grow, although they do not replicate their DNA.

p.7
M Phase and Cytokinesis

What triggers the rapid sequence of cell divisions in early embryonic development?
A) DNA replication
B) Fertilization
C) Cell growth
D) Environmental changes
E) Nutrient availability

B) Fertilization
Explanation: Fertilization initiates a rapid sequence of cell divisions, leading to the formation of an embryo from a single giant cell, highlighting the importance of this event in early development.

p.11
Checkpoints in Cell Cycle Control

What happens if DNA replication is artificially halted in early embryos?
A) The cell enters a resting phase
B) The cell undergoes successful mitosis
C) The cell is driven into disastrous mitosis
D) The cell repairs the DNA
E) The cell stops dividing completely

C) The cell is driven into disastrous mitosis
Explanation: The control system in early embryos does not monitor DNA replication progress, leading to disastrous mitosis if replication is halted by an inhibitor.

p.6
Checkpoints in Cell Cycle Control

Which protein kinase phosphorylates the tyrosine residue on Cdc2, inhibiting its activity?
A) Cdc25
B) MO15
C) Wee1
D) MPF
E) Cyclin B

C) Wee1
Explanation: The Wee1 protein kinase phosphorylates a tyrosine residue on Cdc2, blocking its kinase activity and preventing premature activation of MPF.

p.6
M Phase and Cytokinesis

What is the relationship between MPF and the early embryonic cell cycle in Xenopus?
A) MPF is not involved in the early embryonic cell cycle
B) MPF regulates the size of the egg
C) MPF drives the rapid cell divisions after fertilization
D) MPF prevents the egg from maturing
E) MPF is only active in somatic cells

C) MPF drives the rapid cell divisions after fertilization
Explanation: MPF plays a crucial role in driving the rapid cell divisions that occur in the early embryonic cell cycle of Xenopus, facilitating the development of the tadpole.

p.4
G1 Phase Characteristics

What happens to cells in G1 if appropriate growth factors are not available?
A) They enter the M phase
B) They stop at the restriction point
C) They immediately die
D) They divide uncontrollably
E) They enter the S phase

B) They stop at the restriction point
Explanation: If appropriate growth factors are not available during G1, cells will stop progressing through the cell cycle at the restriction point, leading them to enter a quiescent stage known as G0.

p.3
S Phase and DNA Replication

During which phase does the mitotic spindle begin to form in budding yeast?
A) G1 Phase
B) G2 Phase
C) S Phase
D) M Phase
E) G0 Phase

C) S Phase
Explanation: In budding yeast, although G1 and S phases occur normally, the mitotic spindle begins to form during the S phase, indicating a unique aspect of their cell cycle.

p.12
Role of Cyclins and Cdks

What triggers the activation of cyclin-dependent kinases (Cdks)?
A) The presence of ATP
B) The binding of cyclins
C) The degradation of proteins
D) The completion of mitosis
E) The presence of DNA damage

B) The binding of cyclins
Explanation: Cdks require binding to cyclins for their activity; without this binding, Cdks have no protein kinase activity, which is essential for their function in the cell cycle.

p.9
Cell Cycle Regulation by Extracellular Signals

What is the significance of MPF activity in the cell cycle?
A) It is low during mitosis
B) It peaks every 30 minutes in a cleaving egg
C) It is absent in all eukaryotic cells
D) It is only present in yeast
E) It remains constant throughout the cell cycle

B) It peaks every 30 minutes in a cleaving egg
Explanation: MPF (Maturation Promoting Factor) activity is high during mitosis and low during interphase, with a notable peak every 30 minutes in a cleaving egg, indicating its crucial role in cell cycle regulation.

p.9
M Phase and Cytokinesis

What happens to the nucleated part of an activated egg after constriction?
A) It dies immediately
B) It continues with rapid cleavages
C) It stops dividing
D) It becomes interphase
E) It undergoes apoptosis

B) It continues with rapid cleavages
Explanation: The nucleated part of the activated egg continues with the normal program of rapid cleavages, demonstrating that the nucleus is essential for ongoing cell division.

p.6
G2 Phase Functions

What is the significance of the positive feedback effect in MPF activation?
A) It prevents mitosis from occurring
B) It ensures a gradual increase in MPF activity
C) It leads to a rapid increase in MPF activity
D) It inhibits the activity of Cdc25
E) It stabilizes the cyclin concentration

C) It leads to a rapid increase in MPF activity
Explanation: The positive feedback effect allows active MPF to stimulate further activation of itself, leading to a rapid increase in MPF activity that drives the cell irreversibly into mitosis.

p.3
Quiescent Stage (G0) in Cell Cycle

What happens to animal cells if growth factors are not available during G1?
A) They enter S Phase
B) They undergo apoptosis
C) They enter a quiescent stage called G0
D) They divide immediately
E) They become cancerous

C) They enter a quiescent stage called G0
Explanation: If growth factors are not available during G1, animal cells enter a quiescent stage of the cycle known as G0, where they do not actively divide.

p.13
G1 Phase Characteristics

What must cells coordinate to maintain their size during division?
A) Energy production
B) Growth and division
C) Nutrient absorption
D) Waste elimination
E) Protein synthesis

B) Growth and division
Explanation: To maintain their size, dividing cells must coordinate their growth (increase in cell mass) with their division, although the exact mechanisms of this coordination are still not fully understood.

p.5
Role of Cyclins and Cdks

What is a characteristic of temperature-sensitive cdc mutants?
A) They function well at high temperatures
B) They can only be propagated at high temperatures
C) They fail to function at high temperatures
D) They are resistant to temperature changes
E) They do not affect cell division

C) They fail to function at high temperatures
Explanation: Temperature-sensitive cdc mutants are characterized by their inability to function at high temperatures, which allows researchers to control the timing of cell cycle arrest by changing the temperature.

p.3
Differences in Cell Cycles of Yeasts and Animal Cells

How do budding yeast cells divide?
A) By fission
B) By binary division
C) By budding
D) By fragmentation
E) By mitosis

C) By budding
Explanation: Budding yeast, such as Saccharomyces cerevisiae, divide by budding, where a new bud forms from the mother cell and eventually separates after mitosis.

p.8
M Phase and Cytokinesis

What occurs when a mitotic cell is fused with an interphase cell?
A) The interphase cell dies
B) The interphase cell is driven into mitosis
C) The mitotic cell stops dividing
D) The cells remain unchanged
E) The interphase cell undergoes apoptosis

B) The interphase cell is driven into mitosis
Explanation: Fusing a mitotic cell with an interphase cell exposes the interphase cell to active components in the mitotic cell's cytoplasm, driving it directly into mitosis, regardless of DNA replication.

p.13
S Phase and DNA Replication

During which phase is DNA synthesized in eukaryotic cells?
A) M phase
B) Interphase
C) Cytokinesis
D) G1 phase
E) G2 phase

B) Interphase
Explanation: DNA is synthesized during a specific portion of interphase, which is crucial for preparing the cell for division.

p.12
Role of Cyclins and Cdks

How do cyclin levels change throughout the cell cycle?
A) They remain constant
B) They increase steadily
C) They undergo cycles of synthesis and degradation
D) They only increase during mitosis
E) They decrease during S phase

C) They undergo cycles of synthesis and degradation
Explanation: Cyclins are characterized by their cyclical nature, where their levels rise and fall during each cell cycle, which is essential for the regulation of Cdks.

p.6
Role of Cyclins and Cdks

What is the function of Cdc25 in the regulation of MPF?
A) It phosphorylates Cdc2 to inhibit its activity
B) It removes the inhibitory phosphate from Cdc2
C) It activates Wee1
D) It initiates DNA replication
E) It prevents the accumulation of cyclin

B) It removes the inhibitory phosphate from Cdc2
Explanation: Cdc25 is a protein phosphatase that removes the inhibitory tyrosine phosphate from Cdc2, ultimately activating MPF and allowing the cell to proceed to mitosis.

p.4
Quiescent Stage (G0) in Cell Cycle

What is the G0 phase characterized by?
A) Rapid cell division
B) High rates of protein synthesis
C) Metabolically active but non-proliferating cells
D) Cells undergoing apoptosis
E) Cells preparing for mitosis

C) Metabolically active but non-proliferating cells
Explanation: The G0 phase is a quiescent stage where cells are metabolically active but cease growth and have reduced rates of protein synthesis, allowing them to remain in this state for extended periods.

p.12
Role of Cyclins and Cdks

Which of the following statements is true regarding the number of Cdks in vertebrate cells?
A) There is only one Cdk
B) There are four Cdks
C) There are no Cdks
D) There are two Cdks
E) There are three Cdks

B) There are four Cdks
Explanation: Vertebrate cells contain four distinct Cdks, each interacting with different classes of cyclins to regulate various stages of the cell cycle.

p.5
Differences in Cell Cycles of Yeasts and Animal Cells

What is the significance of the cdc genes in yeast?
A) They are responsible for nutrient absorption
B) They encode components of the cell-cycle machinery
C) They regulate gene expression
D) They are involved in protein synthesis
E) They control cellular respiration

B) They encode components of the cell-cycle machinery
Explanation: The cdc genes are crucial as they encode components necessary for the cell cycle, and mutations in these genes can lead to specific points of arrest in the cell cycle.

p.3
Cell Cycle Regulation by Extracellular Signals

What factors control passage through START in budding yeast?
A) Temperature and light
B) Nutrients, mating factors, and cell size
C) Oxygen levels and pH
D) Genetic mutations
E) Cell age and DNA damage

B) Nutrients, mating factors, and cell size
Explanation: The passage through START in the cell cycle of budding yeast is controlled by the availability of nutrients, mating factors, and the size of the cell, which are essential for proper cell division.

p.13
Cell Cycle Regulation by Extracellular Signals

What is the role of the cell-cycle control system?
A) To produce energy
B) To regulate cell division
C) To synthesize proteins
D) To transport nutrients
E) To eliminate waste

B) To regulate cell division
Explanation: The cell-cycle control system is a complex network of regulatory proteins that governs progression through the cell cycle, ensuring that cell division occurs accurately and in response to various internal and external signals.

p.4
Quiescent Stage (G0) in Cell Cycle

Which type of cells can remain in G0 until stimulated to divide?
A) Muscle cells
B) Neurons
C) Skin fibroblasts
D) Red blood cells
E) Epithelial cells

C) Skin fibroblasts
Explanation: Skin fibroblasts are an example of cells that remain in the G0 phase until they are stimulated by appropriate growth factors to proliferate, particularly in response to tissue damage.

p.12
Role of Cyclins and Cdks

What is the primary function of cyclin-dependent kinases (Cdks) in the cell cycle?
A) To initiate apoptosis
B) To regulate cell cycle events through phosphorylation
C) To synthesize DNA
D) To transport nutrients
E) To repair DNA damage

B) To regulate cell cycle events through phosphorylation
Explanation: Cdks play a crucial role in the cell cycle by regulating major events such as DNA replication, mitosis, and cytokinesis through phosphorylation of intracellular proteins.

p.13
Cell Cycle Regulation by Extracellular Signals

What happens if the cell-cycle control system malfunctions?
A) Cells grow larger
B) Cells stop dividing
C) Excessive cell divisions can result in cancer
D) Cells become dormant
E) Cells produce more organelles

C) Excessive cell divisions can result in cancer
Explanation: A malfunction in the cell-cycle control system can lead to uncontrolled cell division, which is a characteristic of cancer, emphasizing the importance of this regulatory mechanism.

p.12
Role of Cyclins and Cdks

What is the role of M-cyclins in the cell cycle?
A) They promote DNA replication
B) They regulate the restriction point
C) They initiate mitosis
D) They assist in cytokinesis
E) They help in DNA repair

C) They initiate mitosis
Explanation: M-cyclins are specifically involved in promoting the events of mitosis, facilitating the transition from G2 to M phase.

Study Smarter, Not Harder
Study Smarter, Not Harder