Which Of The Following Is True Concerning Cancer Cells?
A) They Do Not Exhibit Density-Dependent Inhibition When Growing In Culture
B) When They Stop Dividing, They Do So At Random Points In The Cell Cycle.
C) They Are Not Subject To Cell Cycle Controls.
D) B And C Only
E) A, B, And C
The correct answer and explanation is :
Correct Answer: E) A, B, and C
Explanation:
Cancer cells exhibit several characteristics that distinguish them from normal cells, especially in how they regulate growth and division. Let’s break down each of the statements:
A) They do not exhibit density-dependent inhibition when growing in culture.
✅ True.
Normal cells grow in a monolayer in culture and stop dividing when they come into contact with neighboring cells — a phenomenon known as density-dependent inhibition. Cancer cells, however, ignore this signal and continue to divide, often piling up on each other, forming clumps or foci. This ability to bypass growth inhibition contributes to tumor formation in tissues.
B) When they stop dividing, they do so at random points in the cell cycle.
✅ True.
Normal cells halt at specific checkpoints (G1, G2, or metaphase) if conditions aren’t favorable or if DNA is damaged. Cancer cells often have defective checkpoint mechanisms due to mutations in genes such as p53 or RB. As a result, if they stop dividing, it isn’t in a controlled, checkpoint-mediated way but rather at unpredictable stages of the cell cycle.
C) They are not subject to cell cycle controls.
✅ True.
This statement highlights one of the core problems with cancer: deregulation of the cell cycle. Cancer cells often have mutations in genes that regulate the cycle — proto-oncogenes (which, when mutated, become oncogenes and promote unchecked division) or tumor suppressor genes (which, when inactivated, fail to halt the cycle under abnormal conditions). Consequently, these cells escape normal control mechanisms and divide uncontrollably.
Conclusion:
Because all three statements (A, B, and C) accurately describe behaviors of cancer cells, the correct choice is E) A, B, and C. Understanding these mechanisms is crucial in cancer biology and developing targeted therapies.