WorksheetsCell cycle
Total questions: 30
Worksheet time: 15mins
What do G1 and G2 phases ensure?
DNA is synthesized correctly
That conditions are suitable and preparations are complete
Cell divides quickly
Cell skips mitosis
The transition from G1 to S phase is crucial because:
Initiates mitosis and cell division
This regulates signals from other cells that control cell proliferation.
Inactivates essential proteins for cell cycle regulation.
Prepares the mitotic spindle for chromosome segregation.
If the attachment of duplicated chromosomes to the mitotic spindle is not properly regulated, what could be the most immediate consequence for the daughter cells?
The unequal chromosome distribution, leading to genetic disorders.
Incorrect DNA replication, causing mutations in the genetic material.
Complete cessation of cell division due to mitotic spindle collapse.
Skipping of the M phase, resulting in early entry into interphase.
Why cyclins important for regulating the cell cycle, despite having no enzymatic activity themselves?
Can provide structural support to the cell-cycle kinases, enabling them to function.
Activate cell-cycle kinases, allowing them to become enzymatically active and trigger cell-cycle events.
Serve as the primary drivers of cell division by directly regulating DNA replication
Inhibit the action of protein kinases, preventing premature cell-cycle progression.
Which mechanism would most likely halt the cell cycle if DNA damage is detected during G1?
Activation of phosphatases
Increased levels of Cdk inhibitors
Degradation of cyclins
Activation of apoptosis signaling during mitosis
A researcher claims that cells in G0 can re-enter the cell cycle under certain conditions. Which observation would best support this claim?
Increased levels of M-Cdk in G0 cells
Expression of cyclins and Cdks in response to growth signals
Complete bypass of S phase in G0 cells
Chromosome alignment during G0 phase
Come up with designing a sequence of events that a cell must follow to transition from G1 to S phase. Which step is essential to initiate DNA synthesis?
Mitogen activation → G1/S cyclin buildup → Rb protein inactivation → DNA synthesis
Cyclin elimination → Mitotic spindle formation → Rb protein activation → DNA synthesis
Phosphorylation of Cdk → Chromosome alignment → Rb protein inactivation → S phase
Cyclin elimination → Chromosome duplication → Rb protein activation → DNA synthesis
Explain the difference in cell division rates between gut epithelial cells and liver cells:
Gut epithelial cells are permanently arrested in G0, while liver cells cycle frequently.
Liver cells spend most of their time in G0, while gut epithelial cells rapidly cycle due to short G1 phases.
Gut epithelial cells divide more slowly than liver cells due to longer G1 phases.
Gut epithelial cells rely more heavily on p53 than liver cells.
Which mechanism ensures that DNA replication occurs only once per cell cycle, preventing re-replication?
S-Cdk inactivates the origin recognition complex (ORC) and Cdc6 through phosphorylation.
DNA damage response inhibits Cdc25, delaying M-phase entry.
The pre-replicative complex is activated by the removal of inhibitory phosphates by Cdc25
Cdc6 accumulates throughout S phase to prevent re-initiation of DNA replication.
Why is the precise regulation of cyclin concentrations critical during the cell cycle?
It ensures cyclins accumulate only when needed and are degraded at the correct time, enabling proper phase transitions.
They allows cyclins to remain active at all times, speeding up the cell cycle
Prevents cyclins from being synthesized during mitosis, ensuring mitotic proteins are activated instead.
Guarantees the continuous activation of cyclins, ensuring uninterrupted progression through the cycle.
What is the primary role of cyclins in the cell cycle?
Breaking down the mitotic spindle
Activating cyclin-dependent kinases (Cdks)
Synthesizing DNA
Forming the nuclear envelope
The mitotic spindle is primarily composed of:
Actin filaments
Intermediate filaments
Microtubules
Collagen fibers
Which checkpoint ensures that all chromosomes are properly attached to the spindle before anaphase begins?
G1 checkpoint
G2 checkpoint
Metaphase checkpoint
S-phase checkpoint
What happens if a cell fails the G1 checkpoint?
It proceeds to S phase regardless.
The cell enters G0 phase or undergoes apoptosis.
Immediately starts mitosis prematurely
It will be checked again
A researcher observes a cell with duplicated DNA but no mitotic spindle formation. Which phase is the cell likely in?
G1 phase
S phase
G2 phase
M phase (prophase)
A mutation prevents the degradation of M-cyclin. What is the most likely outcome?
The cell will fail to exit mitosis.
Cell cycle will end without cytokinesis.
DNA will be replicated multiple times
Resting phase or G0
A scientist notices that a cell has an abnormal number of chromosomes after division. Which regulatory failure likely caused this?
G1 checkpoint fails its task
spindle assembly checkpoint fails
Cdk activation was inhibited
Failure to activate DNA helicase
A cancer cell is observed to bypass all checkpoints, leading to uncontrolled division and tumor growth. What combination of mutations might explain this behavior?
Activation of proto-oncogenes and inactivation of tumor suppressor genes
Increased activation of APC/C and reduced levels of M-cyclin
Overactivation of spindle assembly checkpoints and p53 protein
Reduced activity of Cdks and inactivation of oncogenes
A mutation results in a constantly active Ras protein, which promotes cell cycle progression. What other cellular mechanism must be disrupted for cancer to develop?
Proper attachment of chromosomes to the spindle
Activation of DNA repair enzymes
Loss of functional tumor suppressor genes like p53
Enhanced degradation of cyclins
A cell is exposed to high levels of DNA damage. If the p53 pathway is functional, what is the most likely outcome?
Immediate entry into mitosis
Cell cycle arrest or apoptosis
Activation of APC/C and progression to anaphase
Rapid DNA replication to repair the damage
Which phase of the cell is known for cell growth and preparation for DNA replication?
G1 phase
G2 phase
S phase
M phase
During which phase of the cell cycle does DNA replication occur?
G1 phase
S phase
G2 phase
M phase
What is the final stage of the cell cycle, where the cell divides into 2 daughter cells?
G1 phase
Cytokinesis
M phase
S phase
What happens during the G2 phase of the cell cycle?
DNA is replicated
Chromosomes condense
Cell growth and preparation for mitosis
Cytokenesis occurs
Which of the following is NOT a phase of interphase?
G1 phase
S phase
G2 phase
M phase
During which phase do the chromosomes separate and move toward opposite poles of the cell?
Prophase
Metaphase
Anaphase
Telophase
Which of the following events occurs during telophase?
Chromosomes de-condense
The nuclear envelope re-forms
Spindle fibers disappear
All of the above
Which structure forms to help in the seperation of the chromatids during mitosis?
Spindle fibers
Centrosomes
Nuclear membrane
Centioles
What is the purpose of the G0 phase?
To prepare for cell division
To replicate DNA
To exit the cell cycle and enter a resting state
To form mitotic spindle
What happens if a cell’s checkpoints FAIL?
The cell cycle speeds up
The cell cannot divide
The cell might divide uncontrollably, potentially leading to cancer
Nothing happens
