What is the correct order of the four main stages of the cell cycle?
G1 → S → G2 → M
Which phases make up Interphase?
G1, S, and G2
What happens during the S phase of the cell cycle?
The cell replicates its DNA (Synthesis).
When/why do cells enter the G0 phase?
A “resting” state where the cell is not actively preparing to divide (e.g., neurons). This could be because cells are differentiating or because there are not sufficient resources/need for stem cells to replicate
What is the role of Cyclins and CDKs?
They act as stimulatory proteins that push the cell cycle forward to the next stage.
What is the role of p53?
An inhibitory protein that stops the cycle to repair DNA damage or trigger apoptosis (cell death).
Define Proto-oncogene.
A normal gene coding for a protein that stimulates cell growth and division. examples: growth factors and receptors, cyclins and cdks
Define Tumor Suppressor Gene. Give an example.
A gene coding for a protein that inhibits cell division or repairs DNA to prevent uncontrolled growth. example: p53
What is the difference between a proto-oncogene and an oncogene?
An oncogene is a mutated, overactive version of a proto-oncogene that causes excessive growth.
How do stimulatory and inhibitory proteins represent a car’s mechanics?
Stimulatory (Cyclins) are the gas pedal; Inhibitory (p53) are the brakes. Cancer occurs when the gas is stuck and/or the brakes fail- in most cases both
Why is a mutation in p53 so dangerous for a cell?
If p53 fails, the cell cannot stop to fix DNA errors. It continues dividing with damaged DNA, leading to more mutations and eventually cancer.
Why is a mutation in a proto-oncogene called a “Gain-of-Function”?
The mutation makes the protein hyperactive (too much “gas”), meaning the cell receives constant signals to divide even when it shouldn’t.
Why is a mutation in a tumor suppressor gene called a “Loss-of-Function”?
The mutation disables the protein’s ability to function. In this case to stop the cycle (the “brakes” are cut), allowing unchecked division.
How do Growth Factors interact with Cyclins?
External Growth Factors bind to the cell, triggering a signal that increases the concentration of Cyclins internally, which then activates the cycle.
During which phase of the cell cycle does the cell actively replicate its entire genome?
S (synthesis) stage
Once a cell is fully differentiated, like a mature neuron, often exits the cell cycle to enter a non-dividing state. What is this state called?
G0
Which combination of proteins acts as the primary ‘stimulatory’ engine to push the cell cycle forward?
CDKs and cyclins: Cyclins bind to Cyclin-Dependent Kinases to activate the pathways that move the cell into the next phase.
If a cell detects significant DNA damage at the G1 checkpoint, what is the role of a correctly functioning p53 protein?
It triggers cell cycle arrest or apoptosis.
Using the ‘car analogy’ for the cell cycle, which of the following is the best description of a tumor suppressor gene mutation?
The break line is cut: Tumor suppressors normally act as brakes; a mutation ‘loses’ this function, making it impossible to stop the cycle.
Growth factors are external signals. How do they typically initiate the cell cycle from outside the cell?
They bind to receptors, triggering a cascade that increases cyclin production.
If a mutation causes a Cyclin-Dependent Kinase (CDK) to be active even in the absence of a cyclin, what is the most likely consequence?
The cell cycle will proceed unchecked, even without proper signals.
Which of the following best describes the relationship between the cell cycle and cancer?
A) Cancer is the complete absence of the cell cycle B) Cancer is caused solely by external environmental factors, not internal proteins.
C) Cancer is the result of an accumulation of mutations that bypass cell cycle checkpoints.
D) Cancer only occurs when the S phase is skipped entirely
C. Cancer is the result of an accumulation of mutations that bypass cell cycle checkpoints
What do kinases do?
Kinases add phosphate groups to activate or inhibit various target proteins/enzymes
What happens during the G1 phase?
During the first gap phase of interphase, there is a period of intense cell growh and preparation for DNA synthesis. The checkpoint for passing this phase includes adequate resources and no damage to DNA
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11.1 Genotype, Phenotype, Punnett Squares27
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10.3/10.4 Meiosis and Errors26
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10.2 Mitosis and Differentiation23
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10.1 Cell Cycle25
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9.2 Membrane Transport23
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9.1 Cell Structure and Function33
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8.4 Translation and Mutations34
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8.3 Transcription and Central Dogma30
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8.2 DNA Replication26
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8.1 DNA39
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7.3 Cellular Respiration25
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7.2 Metabolism22
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7.1 Enzyme Structure and Function20
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6.3 Protein Structure and function29
