Not a component of PCR

POLYMERASE CHAIN REACTION (PCR) : PCR is an in vitro DNA amplication procedure in which milions of copies of a paicular sequence of DNA can be produced within a few hours. The flanking sequences of the gene of interset should be known. Two DNA primersof about 20 -30 nucleotides with complementary sequence of the flanking region can be synthesized. STEP 1 :Seperation (Denaturation) : DNA strands are seperated ( melted ) by heating at 95 Degree Celsius for 15 sec to 2 mins. STEP 2 :Priming ( Anneling ) : The primers are annealed by cooling to 50 degree celsius fo 0.5 to 2min. STEP 3 :Polymerization : Nw DNA strands are symnthesized by Taq polymerase.These enzyme is derived from bactris Thermus acquaticus that are found in hot springs.Therefore the enzyme is not denatured at high temperature. The polymerase reaction is allowed to take place 72 degree celscius for 30 sec in presence of dNTPs.Both DNA strands are duplicated in this step. STEP 4 :The steps of 1, 2 and 3 are repeated .In each cycle, the DNA strands are doubled.Thus 20 cycles provide for 1 million times amplificatins. These cycles are generally repeated by automated instument, called Thermal cycler. STEP 5 : After the amplification procedure, DNA hybridization technique or southern blot analysis with a suitable probe, shows the presence of the DNA in the sample tissue. REF :DM VASUDEVAN TEXTBOOK :7th EDITION ; Page no :638