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Laboratory Techniques & Safety Flashcards

7 cards from real PCR practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Laboratory Techniques & Safety flashcards as text

  1. Which workflow direction best prevents amplicon carryover contamination in a PCR laboratory?

    Answer: Reagent prep → sample prep → amplification → post-PCR analysis, never moving backward

    A unidirectional workflow from clean (pre-PCR) to dirty (post-PCR) areas keeps amplified product away from reagents and samples.

  2. In a dUTP/UNG carryover-prevention system, what does uracil-N-glycosylase (UNG) do before thermal cycling?

    Answer: Removes uracil from previously amplified dUTP-containing DNA, preventing its amplification

    UNG excises uracil from contaminating dU-containing amplicons, making them unamplifiable while leaving thymine-containing template intact.

  3. What is the main purpose of aerosol-resistant (filter) pipette tips in PCR setup?

    Answer: To block aerosols from contaminating the pipette barrel and subsequent samples

    Filter barriers stop aerosolized DNA from entering the pipette shaft and cross-contaminating later reactions.

  4. When decontaminating a PCR bench with sodium hypochlorite, which practice is recommended?

    Answer: Use freshly prepared ~10% bleach, allow contact time, then wipe with water or 70% ethanol to remove residue

    Fresh dilute bleach oxidizes DNA, and a follow-up wipe removes corrosive residue that could also inhibit PCR.

  5. A no-template control (NTC) shows amplification. What is the most likely interpretation?

    Answer: Reagents or the workspace are contaminated with target DNA or amplicon

    An NTC contains no template, so amplification signals contamination (or, at late cycles, possible primer-dimer in dye-based assays).

  6. How does UV irradiation inside a PCR workstation help control contamination?

    Answer: It induces pyrimidine dimers in contaminating DNA so it cannot serve as a template

    UV light creates thymine (pyrimidine) dimers that block polymerase extension on contaminating DNA.

  7. Which glove material is generally recommended when handling ethidium bromide-stained gels?

    Answer: Nitrile gloves

    Nitrile provides better chemical resistance against ethidium bromide, a potential mutagen, than latex.

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