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PRINCIPLES
Many
paleontological specimens more than a few thousand years old have DNA
decomposed to such an extent that further study is not indicated. However,
a particular burial situation and other natural factors can occasionally
result in instances of good DNA preservation.
Cost effective identification of these promising
samples is based on the observation that the breaking down of DNA is
similar to the degradation of other molecules present. For example, tests
on the amino acid constituents of associated proteins can be done on large
numbers of samples. These changes are indicative of the amount of DNA
change that can be expected. This is used to choose those samples most
favorable for paleoDNA analysis. |
WHAT IS THE AMINO ACID RACEMIZATION TEST?
Amino acids are the building blocks of proteins. Only
the stereo-configured L amino acids are incorporated into proteins during
biosynthesis. However, the L acids can spontaneously change to D acids,
another stereo-configuration. In living organisms these mutations are
constantly being discarded, but in dead materials, the degenerative
protein changes build up with time.
The amino acid racemization test analyzes the extent of
L to D configuration changes. Aspartic acid is generally used since it has
one of the fastest racemization rates. Other amino acids, for example
alanine and leucine, are also useful. There is a correlation between amino
acid racemization levels and DNA preservation. Also, the relative amounts
of the various amino acids in the protein samples are analyzed and give
further information for subsequent DNA studies. |
