DNA and Smoking

When people talk about smoking and the diseases it cause, most think of lung cancer, emphysema or chronic obstructive pulmonary disease or COPD.  Very few know smoking actually causes genetic damage in various organs through mutations in DNA which can lead to cancers in other organs.  At this point, scientists have associated smoking with at least 17 types of human cancer.

Your DNA is unique to you.  If you remember back to Biology class in high school, it is the genetic or hereditary material found in your cells.  The majority of your DNA is found in the cell nucleus (nuclear DNA), but a small amount is found in the mitochondria (mitochondrial DNA or mtDNA).  DNA can replicate, or make copies of itself, which is important as cells divide and new cells form because “each new cell needs to have an exact copy of the DNA present in the old cell.”  Our DNA is quite good at repairing itself, but over time damage or mutations may occur.  Some mutations are harmless, but others can lead to damage.  If this happens the cell will either stop replicating (or copying), and turn itself off; stop replicating by dying; or continue to divide even though it is abnormal.  When this happens it can lead to cancer.

Scientists are interested in the way DNA mutates and found “a direct link between the number of cigarettes smoked in a lifetime and the number of mutations in the tumor DNA.”   Lung cancers had the highest mutation rates at 150, but smoking-related mutations were also seen in other parts of the body.  Over 5,000 tumors were studied and compared between smokers and non-smokers.  Smokers’ DNA showed “particular molecular fingerprints of DNA damage, called ‘mutational signatures,'” which scientists then “counted how many of these particular mutations were found in the different tumors.”  A smoker with a pack-a-day habit could expect an average of “150 extra mutations in each lung cell every year,” although “the numbers of mutations within any cancer cell will vary between individuals.”

Scientists said the results were a “mixture of the expected and the unexpected.”  They expected to see “mutations caused by direct DNA damage” to those cells that came in direct contact with tobacco smoke, (lungs, mouth, larynx and pharynx).  However, they were surprised at the results from indirect effects found in other parts of the body;  smoking affects these cells in some way that causes them to mutate DNA.

Looking at your DNA, scientists can see the “exposures that caused the mutations that lead to the cancer.”  However, they still don’t understand the causes in the first place.  They do know is that “tobacco smoking seems to accelerate the speed of a cellular clock that mutates DNA prematurely.”   One thing seems clear, smoking dramatically increases your chances for many cancers.

Check out these links for more information on this subject:
Smoking a pack a day for a year causes 150 mutations in lung cells
What happens when DNA becomes damaged?
DNA

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