Question

Please explain why B is the correct answer, I know on the 5'---->3' it goes reverse

and 3'-->5' it goes forward.......I got lost after this. Please explain. Will give a thumbs up.

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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’.

Answer 1

Firstly want to explain that the DNA template is read in 3? to 5? direction and a new strand is synthesized in the 5? to 3? direction.

RNA polymerase uses template strand DNA strands to make a complementary RNA molecule.

The RNA produced is complementary to the template strand and is identical to nontemplate or coding strand, except in RNA, all T nucleotides are replaced with U nucleotides.

In this question, you need a forward primer and a reverse primer which is the reverse complement of 5' -> 3') that matching your input sequence.

Reverse primer anneal to the plus strand, which is oriented in the 5' ? 3' direction. It is also called as the sense or non template strand.

Reverse primer attaches to the stop codon of the complementary strand of DNA (the anti-sense strand).


Forward primer which is complement the minus strand, which is by convention oriented in the 3' ? 5' direction. It is also known as antisense or template strand.

The forward primer attaches to the start codon of the template DNA (the sense strand),

The 5' ends of both primers bind to the 3' end of each DNA strand.