Which of the following sets of primers could you use to amplify the target DNA s

Question

Which of the following sets of primers could you use to amplify the target DNA sequence below, which is part of the last protein-coding exon of the gene involved in cystic fibrosis?
5’- ggctaagatctgaattttccgag … ttgggcaataatgtagcgcctt - 3’
3’- ccgattctagacttaaaaggctc … aacccgttattacatcgcggaa – 5’

a) 5’ GGAAAATTCAGATCTTAG 3’;
5’ TGGGCAATAATGTAGCGC 3’

b) 5’ GCTAAGATCTGAATTTTC 3’;
3’ ACCCGTTATTACATCGCG 5’

c) 3’ GATTCTAGACTTAAAAGGC 5’;
3’ ACCCGTTATTACATCGCG 5’

d) 5’ GCTAAGATCTGAATTTTC 3’;
5’ TGGGCAATAATGTAGCGC 3’.

Explanation / Answer

The answer is (a). If the sequence reads 5' to 3' then the corresponding primer must read 3' to 5'. Looking at the bottom line of both the target sequence and primer (a), we see that they match up 3' to 5' and 5' to 3'. If we compare the bases, they compliment each other, meaning binding will occur. To compare the top lines of sequence, you must reverse the direction of the primer so that they line up 5' to 3' and 3' to 5'. The bases compliment each other once again.

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