A widely used method for calculating the annealing temperature for a primer used in PCR is 5 degrees below the melting temperature, Tₘ(°C), which is computed by the equation 81.5+0.41×(%GC)−(675/N), where %GC is the percentage of GC nucleotides in the oligonucleotide and N is the length of the oligonucleotide. Notice from the formula that both the GC content and the length of the oligonucleotide are variables. Assuming you have the following oligonucleotide as a primer,

5′-TTGAAAATATTTCCCATTGCC-3′

compute the annealing temperature for PCR. What is the relationship between and %GC? Why? (Note: In reality, this computation provides only a starting point for empirical determination of the most useful annealing temperature.) <>

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