Chemistry Reference
In-Depth Information
FIGURE 76
PCR and the amplification of DNA.
During the polymerase chain
reaction there is an exponential increase in the number of copies of the segments
of DNA (the increase is proportional to the number of strands at any given
moment). Thus, if there is only a single strand at the beginning of the reaction,
there will be two after one cycle, four after two cycles, eight after three cycles,
sixteen after four cycles, and so on. After thirty cycles, for example, which only
take a few hours to perform, there will be well over one billion copies of the
original DNA strand.
Collecting samples of ancient nucleic acids is a delicate operation that
requires what are basically surgical procedures. It is advantageous, when-
ever possible, that the samples be collected at excavation sites and precau-
tions taken to ensure that they do not become contaminated with other,
particularly more recent, nucleic acids. At high temperatures and humidity,
nucleic acids decay quickly. Well-preserved ancient nucleic acids can, there-
fore, be expected in sites where low temperatures and a dry environment
prevail, as, for example, in cold, desert areas of the world. Once collected,
the samples need to be isolated from any other remaining materials until
they can be amplified by PCR and their chemical composition and structure
can then be studied.
