I found this article on the following URL: http://dailynews.yahoo.com/h/nm/19991021/hl/dna9_1.html my comments are at the bottom
<< Thursday October 21 7:36 PM ET
DNA damage a culprit in aging
NEW YORK, Oct 21 (Reuters Health) -- Mutations in the DNA found in mitochondria -- the tiny ``powerhouses'' that generate energy in cells -- accumulate over time and may contribute to the aging process, report researchers.
Comparing mitochondrial DNA from healthy young individuals to that of healthy older people, the investigators found that key mutations are more common with age. Scientists led by Dr. Yuichi Michikawa from the California Institute of Technology in Pasadena report the finding in the October 22nd issue of the journal Science.
The researchers found it ``most striking'' that one specific mutation occurred in 8 of 14 (or 57%) of individuals over the age of 65, but in none of the mitochondrial DNA from 13 younger individuals.
Results of a separate analysis of mitochondrial DNA from two sets of stored cells taken 9 to 19 years apart from nine individuals supports the role of age in the accumulation of mitochondrial DNA damage. In at least 3 of the 9 individuals, mitochondrial DNA mutations were evident in the cells taken later in life, but not cells from the same person when they were young.
According to Michikawa and colleagues, these mutations are not inherited but may be caused by free-radicals, unstable compounds formed during normal cell processes. Alternatively, the mutations may be due to cell enzymes that build DNA, or by problems with DNA repair mechanisms.
In an accompanying editorial, Elizabeth Pennisi says the findings provide ``the first hard evidence that mitochondria do deteriorate as people age.'' Just how this deterioration affects the functioning or survival of cells remains to be determined, she adds.
SOURCE: Science 1999;286:664, 774-779. >>
Something the author of this article fails to postulate about, is that this explains why women reach a point in their lives when they are no longer fertile, while men continue to be fertile until death. A woman contributes all of the mitochondrial DNA to her offspring, a man contributes none. If a woman continued to bear children into old age, her children would inherit her damaged mitochondrial DNA. Genetically speaking, a man has nothing to worry about if he bears children in his 80s, his offspring won't have any of his damaged mitochondria.