Multiple Choice
Tumor suppressors are mutated genes that results in higher amounts of gene activity.
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20. Cancer
Oncogenes and Tumor Suppressors
Multiple Choice
In the context of oncogenes and tumor suppressors, how would loss of p53 activity most directly affect a cell?
A
The cell would fail to initiate DNA replication because p53 is the essential helicase required to unwind replication origins.
B
The cell would be less able to arrest the cell cycle or trigger apoptosis in response to DNA damage, increasing survival of genetically unstable cells.
C
The cell would be unable to activate telomerase, leading to immediate senescence in all dividing cells.
D
The cell would have constitutively active Ras signaling because p53 normally functions as a Ras GTPase-activating protein (GAP).
Verified step by step guidance1
Understand the role of p53 in the cell: p53 is a tumor suppressor protein that acts as a transcription factor to regulate the cell cycle, DNA repair, and apoptosis in response to cellular stress or DNA damage.
Recognize that p53 is not a helicase and does not directly participate in DNA replication initiation; instead, it monitors DNA integrity and can halt the cell cycle to allow repair or trigger apoptosis if damage is irreparable.
Analyze the consequences of loss of p53 activity: without functional p53, cells lose the ability to effectively arrest the cell cycle at checkpoints, especially the G1/S checkpoint, and fail to initiate programmed cell death (apoptosis) when DNA damage is detected.
Understand that this failure leads to increased survival and proliferation of genetically unstable cells, which can accumulate mutations and contribute to tumorigenesis.
Note that p53 does not directly regulate telomerase activation nor act as a Ras GTPase-activating protein (GAP), so loss of p53 would not cause immediate senescence or constitutive Ras signaling through these mechanisms.
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