Problem 3 - Campbell Biology

Question

One difference between cancer cells and normal cells is that cancer cells \begin{equation}\begin{array}{l}{\text { (A) are unable to synthesize DNA. }} \\\ {\text { (B) are arrested at the S phase of the cell cycle. }} \\ {\text { (C) continue to divide even when they are tightly packed }} \\ {\text { together. }} \\ {\text { (D) cannot function properly because they are affected }} \\ {\text { by density-dependent inhibition. }}\end{array}\end{equation}

Step-by-Step Solution

Answer

Option C: Cancer cells continue to divide even when they are tightly packed together.

Step 1: Understand the Question

The question is asking to differentiate between cancer cells and normal cells by identifying a specific characteristic that is true for cancer cells but not for normal cells.

Step 2: Analyze Option A

Option A states that cancer cells are unable to synthesize DNA. This is incorrect because cancer cells do replicate their DNA, which is necessary for their uncontrolled division.

Step 3: Analyze Option B

Option B states that cancer cells are arrested at the S phase of the cell cycle. This is also incorrect because cancer cells do not stop at any particular phase and continue to progress through the cell cycle unchecked.

Step 4: Analyze Option C

Option C states that cancer cells continue to divide even when they are tightly packed together. This is correct because cancer cells lose the normal regulatory mechanisms that prevent overgrowth when cells are crowded.

Step 5: Analyze Option D

Option D states that cancer cells cannot function properly because they are affected by density-dependent inhibition. This is incorrect because, in reality, cancer cells are not affected by density-dependent inhibition, which is why they continue to grow uncontrollably even in dense populations.

Step 6: Conclusion

The correct characteristic that differentiates cancer cells from normal cells is found in Option C: cancer cells continue to divide even when they are tightly packed together.

Key Concepts

cell cycle

The cell cycle is a series of stages that cells go through to grow and divide. It comprises four main phases: G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Each phase serves a specific purpose in cell development.

During G1, cells grow and prepare for DNA replication. In the S phase, DNA replication occurs, resulting in two sets of chromosomes. The G2 phase is another growth phase where the cell prepares for mitosis. Finally, during Mitosis, the cell divides into two identical daughter cells.

Normal cells have checkpoints during the cell cycle to ensure everything proceeds correctly. If there's a problem, the cell can undergo apoptosis (programmed cell death) to prevent issues from being passed on. However, cancer cells often ignore these checkpoints, leading to continuous and uncontrolled division.

density-dependent inhibition

Density-dependent inhibition is a crucial regulatory mechanism in cell division. It ensures that cells stop dividing when they become too crowded.

In normal cells, once a certain cell density is reached, signals trigger the cessation of division. This prevents cells from overgrowing and forming layers beyond the initial monolayer.

However, cancer cells lack this inhibition. They do not respond to these regulatory signals, which allows them to continue dividing even in crowded conditions. This absence of response leads to the formation of tumors, as there is no check on their growth in dense cell populations.

uncontrolled cell division

Uncontrolled cell division is a hallmark of cancerous cells. Unlike normal cells, cancer cells bypass the regulatory checkpoints of the cell cycle and continue to divide uncontrollably.

This unchecked division is primarily why cancer cells form tumors. The cells replicate continuously and without the normal limitations imposed by the cell cycle's control mechanisms. Because these cells do not heed signals that typically inhibit proliferation, they accumulate rapidly.

For example, growth factors, which usually stimulate cell division, still affect cancer cells. However, cancer cells continue to divide even without these signals, further emphasizing their loss of normal regulation.

crowded cells

In a healthy organism, when cells become too crowded, they stop dividing. This process is known as contact inhibition and is vital for maintaining tissue structure and function.

Cancer cells, however, do not adhere to this rule. Even when packed tightly together, they keep dividing, piling up on each other, and forming masses or tumors.

Scientists believe that cancer cells lose the ability to communicate with neighboring cells effectively, which explains their relentless growth despite being in a crowded environment. Understanding this behavior is key in targeting cancer treatments to halt or slow down the formation of tumors.