How to xerox DNA!!

We all seen the movies... and heard of DNA fingerprinting etc etc... to catch crooks and murders... Say they get a DNA sample from a crime scene... but its too little... what to do? what to do?... Make copies :D!! Tadaa... The following is a simple explanation as to how DNA is copied..

Ingredients!!

1.DNA sample (Blood, hair, whatever sample you get a hold of)

2.Lots and lots of nucleotides (Adenine, Thymine, Cytosine and Guanine) and Primer sequences

3.DNA polymerase ( Taq polymerase derived from bacterium Thermus aquaticus)

Let’s Xerox

1. Mix the ingredients in a vial

2. Heat the vial at 75-90 oC for 30 seconds: This will unwind the double stranded DNA molecule making each strand available to act as templates upon which new complementary strands can be synthesized.

3. Cool down the vial to 55 oC for about 20 seconds: This allows the primers to bind to the ends of the DNA strand.

4. Raise the temperature of the vial to 75 oC: This is the optimum temperature at which Taq polymerase functions, making copies of the DNA templates.



Mumbo jumbo

It takes less than 2minutes to complete one cycle of DNA duplication using this method- Polymerase Chain Reaction. Meaning 1 million copies of the DNA sample can be made in less than 3 hours.

Taq polymerase used in the process is stable at very high temperatures- No wonder it is derived from Thermus aquaticus a bacteria which hangs around it hot springs- making it uniquely suitable for this reaction.

Now why did we use primers? DNA polymerase cannot start copying a chain of DNA without a short sequence of nucleotides to initiate the process. Primers are simply short sequences of nucleotides which attaches to the ends of the template DNA strands so that the polymerase can start working.

Reference

Mckee, T., & Mckee, J.R. (2003). Biochemistry, the molecular basis of life (3rd ed.). New York; McGraw-Hill Companies Inc.