Dna Damage and Repair

DNA can be extracted from human cells or tissues and then analyzed chemically for its components. There are various assays to detect DNA modifications. Some of these techniques are very sensitive and can detect rare changes in DNA. They include a number of chemical analyses and chromatographic measurements of DNA. A hotly debated issue is the choice of method to purify DNA from cells or tissues. Many of the available extraction procedures introduce new DNA damage in the process of purification. A number of enzymatic methods have been used in which specific enzymes or antibodies detect certain kinds of DNA base modifications and/or adducts formed in DNA. These enzymes become molecular "probes" for the damage, an approach that can be very sensitive. Radioactive labeling procedures can be a simple and easy way to measure several modifications in DNA.

The free radical theory of aging was first put forward by Denham Harman in 1956. He proposed that free radicals would be produced in the utilization of molecular oxygen by animal cells, and that as a consequence of free radical reactions with nucleic acids and other cellular components, the animal would develop mutations and cancer. He also suggested that damage by endogenous free radicals was the fundamental cause of aging. A second theory, proposed in 1959 by Leo Szilard, postulated specifically that time-dependent changes in somatic DNA, rather than other cellular constituents, were the primary cause of senescence. Both authors based their theories in large part on the belief, common at the time, that radiation accelerated aging independently of its effects on carcinogenesis.