Cancer includes many diseases that share a central feature: uncontrolled cell growth. This lesson explains how DNA replication errors can accumulate, how those errors may contribute to tumor formation, and how mutations in proto-oncogenes can speed up the cell cycle.
Cell-cycle checkpoints monitor whether important events have been completed before a cell advances. One important checkpoint function is to monitor proper DNA replication during the S phase. Although control and repair systems are extensive, they do not catch every error. A small proportion of replication errors, called mutations, may remain in the DNA and be inherited by daughter cells.
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How can an uncorrected DNA replication error affect later generations of cells?
It can be copied during cell division and inherited by daughter cells, where it may contribute to further changes.
How are proto-oncogenes and oncogenes related?
A proto-oncogene is a normal gene for a positive cell-cycle regulator; an alteration that drives progression too strongly can convert it into an oncogene.
What role do tumor suppressor genes play in cell-cycle control?
They code for negative regulators that can halt cell-cycle progression when conditions are unsuitable.
How does p53 help respond to DNA damage?
It can signal repair processes, promote p21 production, and trigger apoptosis if damage cannot be adequately addressed.
Why can loss of p53 function contribute to tumor growth?
Damaged cells may continue through the cell cycle, avoid apoptosis, and pass mutations to descendants.
Quiz questions
During which cell-cycle phase is DNA replicated?Answer: S phase.
What is a proto-oncogene?Answer: A normal gene that codes for a positive cell-cycle regulator.
What makes an altered gene an oncogene, as described in these notes?Answer: It increases the rate of cell-cycle progression and can contribute to cancer.
If Cdk becomes active without partnering with cyclin, what may happen?Answer: The cell may pass a checkpoint before required conditions are met.
Why does one mutation not necessarily produce a tumor?Answer: The affected cell may be unable to continue dividing and pass the mutation on.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.