Remembering that DNA polymerases can only add nucleotides to the 3′ end of DNA design = forward primer and reverse primer; each 10 bases long; amplify target sequence of the DNA that is at least 100 bp long: Write the sequence of the primers below; with their 3′ and 5′ ends indicated.

/ Exams & Certification / By

Remembering that DNA polymerases can only add nucleotides to the 3′ end of DNA design = forward primer and reverse primer; each 10 bases long; amplify target sequence of the DNA that is at least 100 bp long: Write the sequence of the primers below; with their 3′ and 5′ ends indicated. Also indicate on the sequence above which strand they are complementary to (will anneal to). Forward primer sequence: 5′ AGGAAGGTGG 3′ Reverse primer sequence: 5′ CTTCTGCAAG 3

The Correct Answer and Explanation is:

To design forward and reverse primers correctly for amplifying a DNA sequence, it is essential to understand both the directionality of DNA strands and the role of DNA polymerase. DNA polymerase can only synthesize DNA in the 5′ to 3′ direction, meaning primers must bind to the 3′ ends of the template strands and point toward each other across the target region.

Given:

  • Forward primer: 5′ AGGAAGGTGG 3′
  • Reverse primer: 5′ CTTCTGCAAG 3′
  • Target region is at least 100 base pairs long

Explanation of Primer Function:

  1. Forward Primer (5′ AGGAAGGTGG 3′)
    • This primer is identical to a segment of the sense (coding) strand of the DNA.
    • It will anneal to the antisense (template) strand, binding from 3′ to 5′ on that strand.
    • DNA polymerase will then extend this primer in the 5′ to 3′ direction, copying the sense strand.
  2. Reverse Primer (5′ CTTCTGCAAG 3′)
    • This primer is complementary to the sense (coding) strand, and will anneal to it from 3′ to 5′.
    • It binds downstream (after 100 base pairs) from the forward primer.
    • DNA polymerase extends this primer in the 5′ to 3′ direction, copying the antisense strand.

To check correctness, let’s reverse-complement the reverse primer to find what it will bind to:

  • Reverse primer: 5′ CTTCTGCAAG 3′
  • Reverse complement: 5′ CTTGCAGAAG 3′

This reverse complement matches a part of the coding strand, meaning the primer will anneal to the coding strand (and copy the antisense strand).

Summary of Primer Roles:

  • Forward primer (5′ AGGAAGGTGG 3′) binds to the antisense strand
  • Reverse primer (5′ CTTCTGCAAG 3′) binds to the sense strand

This arrangement allows PCR to amplify a double-stranded DNA region of at least 100 base pairs lying between the two primers.

Related Posts

Scroll to Top