Question

Normally, many regulatory mechanisms signal a cell when it should divide and when it should stop dividing. Tumors arise when cells either proceed through the cell cycle without a start signal, or fail to respond to signals that normally stop cell division. During cell division a checkpoint  is a stage in the eukaryotic cell cycle at which the cell examines internal and external cues and "decides" whether or not to move forward with division. What are three checkpoints of the cell cycle and what is the cell "checking" for?

Cancer cells are cells gone wrong — in other words, they no longer respond to many of the signals that control cellular growth and death. Cancer cells originate within tissues and, as they grow and divide, they diverge ever further from normalcy. A cancerous tumor can be invasive; cells can enter the blood and lymph and metastasize to other areas of the body and develop secondary tumors. Discuss ways that cancer cells behave differently then normal cells.

Answer 1

Check points are the stages where a cell cycle may be stopped if the circumstances are unfavorable for the cell division. At every check point, the cell checks if it is ready to enter the next phase of the cell cycle.

The 3 checkpoints of the cell cycle are:

1.G₁/S - checks extracellular growth factors or mitogens and intracellular nutritional state

2. G₂/S - Ensures DNA replication success

3. Spindle checkpoint- Around late Metaphase or early Anaphase. Checks whether all the chromosomes are attached to the spindle fibers or not.

Specific changes to the genes in one cell or group of cells might cause cancer. These cells divide and grow uncontrolled, resulting in the tumor formation. The most important distinguishing feature is expression of much greater Telomerase as compared to normal cells. These cells avoid immune destruction, activate invasion and metastasis, resist cell death, possess genome instability and mutation , escape growth suppressors.