PCR PCR Reagents & Consumables Management

Question 1

What is the primary reason PCR-grade water (nuclease-free water) must be used instead of regular distilled water in PCR reactions?

Accepted Answer

To eliminate DNase and RNase that would degrade template and primers

Answer

To increase ionic strength of the reaction

Answer

To improve thermostability of Taq polymerase

Answer

To lower the melting temperature of the amplicon

Question 2

Which buffer component in a standard PCR master mix is critical for stabilizing Taq DNA polymerase activity and must be verified when troubleshooting failed reactions?

Accepted Answer

Magnesium chloride (MgCl₂) concentration

Answer

Potassium chloride concentration

Answer

Glycerol percentage

Answer

BSA concentration

Question 3

When storing a prepared PCR master mix containing dNTPs and primers at -20°C, what is the recommended maximum number of freeze-thaw cycles before reagent degradation becomes a concern?

Accepted Answer

No more than 5–10 freeze-thaw cycles

Answer

Up to 50 freeze-thaw cycles

Answer

Freeze-thaw cycles have no effect on PCR reagents

Answer

No more than 2 freeze-thaw cycles

Question 4

Which class of PCR consumables must be certified as 'low-retention' or 'thin-walled' to ensure accurate thermal transfer and prevent sample loss during reaction setup?

Accepted Answer

PCR tubes and 96-well plates

Answer

Pipette tips only

Answer

Microcentrifuge tubes for storage

Answer

Gel electrophoresis combs

Question 5

What is the purpose of including a 'hot-start' enzyme component in a PCR master mix?

Accepted Answer

To prevent non-specific amplification and primer-dimer formation at room temperature during setup

Answer

To increase the extension speed of the polymerase

Answer

To eliminate the need for a denaturation step

Answer

To allow PCR to run at a lower annealing temperature

Question 6

Which reagent additive can be included in a PCR master mix to reduce secondary structure in GC-rich templates and improve amplification efficiency?

Accepted Answer

DMSO (dimethyl sulfoxide) at 5–10%

Answer

Ethanol at 70%

Answer

SDS at 0.1%

Answer

EDTA at 5 mM