Page 16 - An Identity Crisis

PCR Technology

PCR is the cornerstone of current forensic DNA analysis, as well as many other biological disciplines,
such as drug discovery and disease diagnosis. PCR was invented in the mid-1980s by Dr. Kary Mullis,
who was awarded the Nobel Prize in Chemistry in 1993 for this revolutionary breakthrough. The
concept of PCR resembles a biological photocopier. This sensitive technique is capable of producing
millions, even billions of copies of DNA from just a few input strands (templates) of DNA. Once copied
a billion-fold, this small amount of original DNA can be visualized using gel electrophoresis in cases
where, prior to this process, it was undetectable.

Ingredients of PCR:

TEMPLATE DNA: the input DNA to be copied (DNA triphosphates) is a collective term for any, or all,
from the crime scene) bases.

This DNA is obtained by extracting it from a cell’s PCR BUFFER: the solution in which PCR occurs
nucleus and separating it away from proteins and
other cellular components. A solution containing precise concentrations of salts
and magnesium that facilitate an ideal environment
PRIMERS (FORWARD AND REVERSE): for PCR to occur.
“bookends” used to define the region of junk DNA to
be copied TAQ POLYMERASE: the enzyme responsible for
copying pieces of the DNA
Primers are short pieces of DNA synthesized in
a laboratory that bind to DNA adjacent to the This enzyme was isolated from a bacterium
polymorphic, or variable, region. Each section of (Thermus aquaticus) originally found in hot springs.
DNA used for amplification requires two primers, In order to survive in this hostile environment, this
a forward and reverse, to define the start and stop bacterium evolved a specialized enzyme to replicate
point for the reaction. DNA at temperatures that would normally prevent
enzymatic activity. This heat-stable enzyme is
DNTPS: the building blocks of DNA crucial to the PCR technique, as it assembles raw
components into the desired PCR products under
PCR products are made from the same building the higher temperatures needed for the reaction.
blocks as DNA. dNTPs (deoxynucleotide

16 THE MYSTERY OF LYLE AND LOUISE