Q14TYU Shown here are two HeLa cancer c... [FREE SOLUTION]

Chapter 12: Q14TYU (page 234)

Shown here are two HeLa cancer cells that are just completing cytokinesis. Explain how the cell division of cancer cells like these is misregulated. Identify genetic and other changes that might have caused these cells to escape normal cell cycle regulation.

Short Answer

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The division of cancer cells is misregulated because it skips the normal checkpoints of the cell cycle. Thus, it undergoes uncontrolled division and is thus considered immortal.

Mutation of genes is one of the reasons that result in the abnormal cell-cycle control system. Cancer cells might also have a defect in the signaling pathway.

Step by step solution

Cancer cells

A group of uncontrolled growing and dividing cells is called cancer cells. These cells divide rapidly, and the uncontrolled division of these cells eventually leads to the development of tumors.

The cancer cells have abnormal regulation of the cell cycle; they escape apoptosis. These cells also can move to different parts of the body (metastasis) and form new blood vessels (angiogenesis).

Cancer cell division is misregulated

Cancer cells develop from changes that occur in the cell cycle control system. Various checkpoints in the cell cycle are landmarks. These allow the cell to move from one stage to the next.

The checkpoints are essential because the phases are irreversible. Thus, cells are monitored at checkpoints for the normal functioning and division of cells.When the checkpoint senses any defect in the chromosome material of the cell, then the cell cycle stops.

The cell then tries to repair the damage in the DNA. If it cannot fix the damage, the cell undergoes programmed cell death (apoptosis), and the defected cell is destroyed. However, cancer cells seem to avoid these checkpoints.

Cancer cells do not stop dividing at the checkpoints like normal cells do and pass the G₁ and G₂ checkpoints. As a result, these cells undergo indefinite division due to misregulation, leading to tumor development.

Causes that affect cell-cycle regulation

One of the common genetic reasons associated with cancer cells is mutation. Any change in the nucleotide sequence of the DNA is a mutation. Mutation in the genes that produce defective protein often results in abnormal cell cycle control.

Thus, the cells acquiring mutation have disabled checkpoints that control the division of cells. As a result of disabled checkpoints, the cell undergoes uncontrolled division to form cancer cells.

The culture of cancer cells indicates that they don't require growth factors to grow and divide. This is because these cells can synthesize their growth factors, due to which they grow indefinitely.

These cells may have irregular signaling pathways that provide growth signals to the cell's cycle control system without growth factors. As a result, the cells continue to grow divide.

Thus, genetic and cellular changes lead to cancer cells' development as these cells escape cell cycle regulation.