DAP

Denaturation

heated to 95^oC >

H bonds b/w complementary bases of dsDNA fragments break >

dsDNA separates > ssDNA

Annealing DNA primers

cooled to 65^oC >

primers cbp w/ comp. seqs @ 3' end of target seqs in ssDNA >

primers provide free 3' -OH end for Taq pol to add dNTPs to elongate new DNA strand >

DNA primers added in excess to prevent ssDNA from reannealing

Primer extension

temp increased to 72^oC >

optimum temp of Taq pol. Taq pol synthesises rest of new DNA strand by adding dNTPs to 3' -OH ends of both primers by catalysing formation of phosphodiester bonds b/w adjacent dNTPs >

each primer lengthened into new DNA strand, each newly synthesised DNA strand complementary to target DNA seq, each ssDNA obtained after Denaturation now dsDNA >

no. of dsDNA molecules after n cycles = 2ⁿ

Review: H2 Biology 11 - Molecular techniques