RSS Feed (xml)

Powered By

Skin Design:
Free Blogger Skins

Powered by Blogger

Senin, 21 Juni 2010


Some time ago I wrote an article about how cancer develops?now I'll write a continuation of the article, how the cancer can develop in our body. While each human cell performs its own specialized function, it also exerts influence on the cells around it. Cells communicate with one another via receptors, protein molecules on the cell surface. A cell releases chemical messages, which fit into the surface receptors of cells nearby, much as a key fits into a lock. A cell may instruct other cells in its neighborhood to divide, for example, by releasing a growth-promoting signal, or growth factor.

The growth factor binds to receptors on adjacent cells, activating a message within each individual cell. This message travels to the nucleus, where a cell’s genes are located.

1. Proto-Oncogenes Become Oncogenes

When the growth factor message reaches the cell nucleus, it activates genes called proto-oncogenes. These genes produce proteins that stimulate the cell to divide. In cancerous cells, mutations in proto-oncogenes cause these genes to malfunction.

When a proto-oncogene mutates, it becomes an oncogene—a gene that instructs the cell to grow nd divide repeatedly without stimulation from neighboring cells. Some oncogenes overproduce growth factors, causing the cell to divide too often.

Other oncogenes stimulate the cell to reproduce even when no growth factor is present. Cancer researchers have identified about 100 different types of proto-oncogenes and their cancer-causing oncogene counterparts.

2. Tumor Suppressor Genes Stop Working

When runaway cell division occurs, it does not necessarily lead to cancer. Neighboring cells respond by excreting a growth inhibitor. This chemical binds to receptors in the malfunctioning cell, sending a signal to the nucleus that activates tumor suppressor genes. Tumor suppressor genes are like brakes for cell growth.

When activated, these genes halt the cell cycle, preventing further cell division. But if tumor suppressor genes malfunction due to mutations, the rapidly dividing cell ignores messages from its neighbors telling it to stop dividing. Malfunctioning tumor suppressor genes are not enough to cause cancer—the cell still must overcome a host of other safety mechanisms before it can cause truly significant damage.

3. Cell Cycle Clock Malfunctions

The cell nucleus contains a collection of interacting proteins that control cell division. Sometimes called the cell cycle clock, this group of proteins interprets incoming messages at several checkpoints in the cell division cycle.
At these checkpoints, the clock evaluates the health of the cell. If conditions are right, the clock activates certain proto-oncogenes, which produce proteins that trigger the cell to enter the next stage of the cell cycle. If conditions are not right, certain tumor suppressor genes produce proteins that prevent the cell from proceeding with cell division.

1 komentar: