PCR Primer Design & Optimization

Question 1

What is the optimal melting temperature (Tm) range for most PCR primers?

Accepted Answer

55–65°C

Answer

A Tm of 55–65°C allows primers to anneal specifically without being too stringent or too loose under standard PCR conditions.

Question 2

Which of the following primer characteristics is most likely to cause primer-dimer formation?

Accepted Answer

Complementarity between the 3' ends of forward and reverse primers

Answer

Complementarity at the 3' ends allows primers to anneal to each other and be extended by polymerase, generating primer-dimer artifacts.

Question 3

What GC content range is generally recommended for PCR primers?

Accepted Answer

40–60%

Answer

A GC content of 40–60% provides adequate stability while minimizing secondary structure formation and non-specific binding.

Question 4

Why is it generally advisable to end a primer with a G or C nucleotide at the 3' terminus?

Accepted Answer

A G or C clamp stabilizes primer-template binding at the extension site

Answer

A GC clamp at the 3' end provides stronger hydrogen bonding, ensuring stable and efficient primer annealing for extension initiation.

Question 5

The annealing temperature (Ta) in a PCR protocol is typically set how many degrees below the primer Tm?

Accepted Answer

5–10°C

Answer

Setting Ta 5–10°C below Tm ensures efficient primer annealing while maintaining adequate specificity.

PCR - Polymerase Chain Reaction Certification Practice Test