Sunday, June 6, 2010

Smoking and Damage to the Genome

Good morning. We had a fun evening of gaming over at Clay's last night. Sorry, but Blarney was partially eaten.

I came across an interesting recent story dealing with a smoker and the impact smoking has on our DNA: The story is reported here. 50,000 mutations in a tumor, and the complete failure of the error-correcting mechanisms in the DNA, leads to a scary outcome for Mr. Smoker. From the author's calculations in the story, each time the smoker smoked 3 cigarettes, a new mutation in the tumor was created!

One Man, One Tumor, Tens of Thousands of Mutations

Posted by Kristie on May 26, 2010

A team of researchers at Genentech in California compared the genome, all the genes present in DNA, from cells in healthy tissue with the genome of cells in lung tumor tissue from the same patient. This 51 year old man smoked about 25 cigarettes a day for 15 years. Researchers looked at the number of mutations, genetic changes in DNA in this case primarily caused by toxins in cigarette smoke, between the tumor and healthy tissues. What they found was astounding.

Cancer is usually the result of an accumulation of mutations over a long period of time but researchers were not ready for what they found in this patient's tumor tissue. The tumor tissue contained 50,000 genetic mutations in the man's genomic DNA. Researcher Zemin Zhang said his team was so shocked that they rechecked their work to make sure their results were correct.

Zhang calculated three cigarettes per mutation found in the tissue of this patient. See the calculations below:

(25 cigarettes/day x 365 days/year = 9125 cigarettes/year; 9125 cigarettes per year x 15 years =136875 cigarettes; 136875 cigarettes/50,000 mutations = 2.7 cigarettes/1 mutations –round up to 3)…

(Back to Tom again) Here is what I think is a helpful description of how things like a tumor or even cancer can be created in our cells: Cancer is a multistep process. First initiation then promotion. In some (heck a lot) of cases a single point mutation can occur and elude repair mechanisms. At some point a promotion event occurs and that single point mutation is fixed in the cell genome. Once that happens the cell can begin to divide without restraint and the tumor growth begins.

It does not take an accumulation of mutations over time to cause cancer. That some tumors may have an accumulation of mutations may be more a factor of the lack of control over cell division as a result of the initial event/damage to the DNA.

So what does this all mean? I don't have a clue. But it is interesting to me that the researchers tried to tie in the amount of cigarettes with the amount of mutations. I don't think that's how tumors / cancer work (see the comment after the story excerpt.) But if anyone has some helpful additions to this, I would be interested in learning more about it. But for now, if you are going to smoke, smoke only 2 cigarettes, don't touch that third! /s/Tom

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