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Thursday, May 10, 2007

Genetic Damage During Cell Division:

All living cells have a limited ability to renew themselves. This ability confers a specific life span that appears to be pre-programmed into their chromosomes. When cells divide, the ends of the DNA molecules get shorter, truncating a section of the chromosome called the telomeres. The DNA strands get shorter and shorter until the cell can no longer replicate itself.

Almost all of the cells in our body, including mesothelial skin cells, will grow old and die. The only exceptions are bone marrow cells (making blood cells) and the sperm producing cells of the testes. These cells are called immortal cells since they never lose the ability to reproduce themselves. They are assisted during cell division by an enzyme called telomerase that allows them to keep dividing endlessly without degrading. Before regular cells get old and die they divide, and new cells, (daughter cells) take their place. This process, called mitosis, can be repeated roughly 60 to 100 times during the human lifespan before the cells lose their ability to divide. Once that happens, our tissues and organs begin to fail and we reach the end of our lifespan.

It is during mitosis of respiratory tissue cells that asbestos fibers are thought to do the damage that eventually leads to mesothelioma. During mitosis, the DNA in the parent cell is split into two haves and each half is drawn towards an opposite end of the cell. There, new amino acids replace the missing halves of the DNA by using the original halves as templates. Assuming nothing goes wrong, the cell now contains two identical sets of DNA and a barrier forms that divides the cell into two identical halves.

During mitosis, asbestos fibers that have penetrated the cell are thought to physically interfere with the replication of the DNA. This may break the DNA chains, causing the cell to fail, or damage the functioning of its genes, making it become cancerous. The majority of cells whose genetic machinery is non-functional will die and be cleaned up by the immune system but not all of them will. Some cells whose genetic machinery wasn't fatally damaged will continue to live on in a diminished or damaged state. Those malfunctions which cause a regular cell to reproduce endlessly are termed cancer.

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