Technical Skills & Application Flashcards

When calibrating a spectrophotometer, which solution should be used to set the 100% transmittance (zero absorbance) baseline?

Answer: A blank reagent solution

A blank reagent solution (containing all reagents except the analyte) is used to zero the instrument, accounting for any absorbance from the reagents themselves.

In a laboratory performing PCR, a technician observes amplification in the no-template control (NTC). What is the most likely cause?

Answer: Contamination of reagents or workspace with DNA

A positive NTC result indicates DNA contamination of reagents or the workspace, as no template was added to that reaction.

Which statistical measure is most appropriate for describing the spread of a skewed dataset in a clinical laboratory context?

Answer: Interquartile range (IQR)

The IQR is preferred for skewed distributions because it is not influenced by extreme outliers, unlike standard deviation.

A scientist needs to prepare 500 mL of a 0.1 M NaCl solution (MW = 58.44 g/mol). How many grams of NaCl are required?

Answer: 2.92 g

Moles needed = 0.1 mol/L × 0.5 L = 0.05 mol; mass = 0.05 × 58.44 = 2.92 g.

In Western blotting, what is the primary purpose of the blocking step?

Answer: To prevent non-specific antibody binding to the membrane

Blocking (e.g., with milk or BSA) saturates non-specific binding sites on the membrane so that antibodies only bind the target protein.

Which type of pipette is most appropriate for accurately dispensing 0.75 mL of a reagent?

Answer: Micropipette set to 750 µL

A micropipette set to 750 µL provides the greatest accuracy and precision for volumes in the sub-millilitre range.

When performing a Gram stain, what is the role of the decolorizing agent (acetone-alcohol)?

Answer: It removes crystal violet from Gram-negative cells

The decolorizer extracts crystal violet from Gram-negative cells (which have thinner peptidoglycan and an outer membrane), leaving them colourless before counterstaining.