Magazine article Science News

DNA from Dinosaurs: Impossible Dream?

Magazine article Science News

DNA from Dinosaurs: Impossible Dream?

Article excerpt

Molecular biologists have been tripping over each other in recent years in the race to retrieve samples of DNA from dinosaur bones and other fossils. Now, new research challenges these claims of finding ancient DNA.

Molecules of DNA fall apart after a few thousand years and are unlikely to have survived from the time of the dinosaurs, more than 65 million years ago, report Hendrik N. Poinar of the University of Munich and his colleagues. "The prospects of retrieving DNA sequences from dinosaur fossils seem bleak," the scientists report in the May 10 Science.

Poinar and his coworkers describe a quick, simple test that reveals whether DNA in old samples has degraded or been contaminated by modern genetic material. Their technique focuses on amino acids-the building blocks of proteins-which come in right-handed and left-handed forms. Most organisms build proteins using only left-handed amino acids, known as L-enantiomers. After death, a chemical reaction called racemization changes L-enantiomers into right-handed D-enantiomers until a balance is reached.

The racemization reaction for one amino acid-aspartic acid-proceeds at about the same rate as DNA degradation. Scientists can therefore use aspartic acid's ratio of D- to L-enantiomers as an independent means of authenticating DNA extracted from old samples, proposes Poinar's group. If extensive racemization has occurred, the original DNA will have deteriorated. In such cases, any DNA extracted from a sample must come from a modern contaminant, say the scientists. …

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