PCR Primer Design & Optimization 2

Question 1

What is the recommended primer length range for standard PCR applications?

Accepted Answer

15–30 nucleotides

Answer

Primers of 15–30 nucleotides are long enough to be specific while short enough to anneal efficiently under standard PCR conditions.

Question 2

Which in silico tool is most commonly used to check primer specificity against a genome database?

Accepted Answer

BLAST (Basic Local Alignment Search Tool)

Answer

BLAST aligns the primer sequence against a reference database to identify potential off-target binding sites that could reduce specificity.

Question 3

A hairpin structure in a primer is problematic primarily because it:

Accepted Answer

Sequesters the 3' end, preventing template binding and extension

Answer

Intramolecular hairpin loops fold the primer on itself, sequestering the 3' end and preventing it from annealing to and being extended on the template.

Question 4

When designing primers for a region with high GC content, which modification can improve amplification efficiency?

Accepted Answer

Adding DMSO (dimethyl sulfoxide) to the PCR reaction

Answer

DMSO destabilizes GC-rich secondary structures in the template, improving denaturation and primer access in high-GC regions.

Question 5

Primer concentration in a standard PCR reaction is typically in which range?

Accepted Answer

0.1–0.5 µM

Answer

Primer concentrations of 0.1–0.5 µM (100–500 nM) provide sufficient primers for amplification without promoting non-specific products or primer-dimer formation.

PCR - Polymerase Chain Reaction Certification Practice Test

PCR - Polymerase Chain Reaction Certification Practice Test

PCR Primer Design & Optimization 2