When normal human cells are grown in a culture plate, they typically stop growing once a monolayer of cells is formed at the bottom of the plate. This arrest in division is an example of? Group of answer choices Growth factor-induced division Malfunction of the cell cycle checkpoints Density-dependent inhibition Anchorage-dependence cell division
The correct answer and explanation is:
The correct answer is: Density-dependent inhibition
Explanation (300 words):
When normal human cells are grown in a culture plate, they proliferate until they cover the surface of the plate in a single layer called a monolayer. At this point, they stop dividing, a phenomenon known as density-dependent inhibition or contact inhibition.
Density-dependent inhibition is a regulatory mechanism where cells stop dividing when they come into contact with each other. This process is essential for maintaining proper tissue architecture and preventing overcrowding. Once cells form a monolayer and fill the available space, they send signals through cell surface receptors that inhibit further cell division. This is a natural way cells regulate growth and ensure that tissues do not grow uncontrollably.
This contrasts with cancer cells, which often lose this property. Cancer cells can grow over one another and form multilayers because they no longer respond to density-dependent inhibition. This loss of contact inhibition is a hallmark of cancerous transformation.
Let’s clarify why the other options are incorrect:
- Growth factor-induced division: Growth factors are molecules that stimulate cells to divide, but density-dependent inhibition happens even when growth factors are present. The arrest is due to cell-to-cell contact, not lack of growth factors.
- Malfunction of the cell cycle checkpoints: Cell cycle checkpoints control the fidelity of cell division, preventing damaged or incomplete DNA from passing on. The arrest in division due to monolayer formation is a normal, regulated process, not a malfunction.
- Anchorage-dependence cell division: Anchorage dependence means cells need to be attached to a surface (like the culture plate) to divide. While normal cells show anchorage dependence, the specific arrest after monolayer formation is due to density-dependent inhibition, which is a different mechanism.
In summary, density-dependent inhibition ensures that normal cells stop dividing when they become too crowded, maintaining tissue organization and preventing uncontrolled growth.