the polymerase chain reaction and gel electrophoresis

what is the polymerase chain reaction

• a manipulation technique that amplifies DNA by making multiple identical copies.

• Used by scientists when there is an insufficient amount of DNA sample for testing

• focus on certian genes through primers or restricition endonucleases

• after each cycle DNA present is doubled

step by step process of polymerase chain reaction

1. denaturation - the DNA stramd is heated to approx 90-95 to break the hydrogen bonds between the bases and seperate the strands forming a single stranded DNA

2. annealing - the single stranded DNA is cooled to approx 50-55 to allow the primers to bind to complementary sequences on the single stranded DNA

3. elongation - DNA is heated again to 72 which allows taq polymerase to work. Taq polymerase binds to the primer which acts as a staring point, and begins synthesing a new complementary strand of DNA

4. repeat - the process is repeated multiple times to create more copies of DNA

what is taq polymerase

• a heat resistant DNA polymerase enzyme which amplifies a single strandted molecue by attaching com nucleotides

forward primer

• the forward primer will bind to the start codon at the 3’ end of the template strand. This causes taq polymerase to synthesis a new DNA strand in the same direction that RNA polymerase would function

reverse primer

• the reverse primer will bind to the stop codon at the 3’ end of the coding strand. This causes taq polymerase to synthesis a new DNA strand in the reverse direction that RNA polymerase would function

what is gel electrophoresis

• a lab technique that seperates prepared DNA fragments (from restriction endonuclease or pc) based on molecule size

reading gel electrophoresis

• a standard ladder contains a number of DNA fragments with a known molecular size

• molecular size indicates the length of a nucleic acid sequence

short tandem repeats

• STRs are segments of DNA that contain repeats of 2-6 nucleotides found in the non-coding regions of DNA

• everyone has two copies of each STR region (one from mum and one from dad)

• there are many fixed locations where STRs are located on our chromosome