Practice Test GeeksPCR - Polymerase Chain Reaction Certification Practice Test
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Sample Preparation & Nucleic Acid Extraction 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 Sample Preparation & Nucleic Acid Extraction flashcards as text

  1. What A260/A280 ratio is generally considered indicative of pure DNA?

    Answer: ~1.8

    Pure DNA has an A260/A280 ratio of about 1.8; lower values suggest protein or phenol contamination.

  2. A DNA extract has A260/A280 of 1.85 but A260/A230 of 0.9. What is the most likely contaminant?

    Answer: Chaotropic salts such as guanidine, or carbohydrates

    A low A260/A230 ratio indicates contaminants absorbing at 230 nm, such as guanidine salts, phenol, or carbohydrates.

  3. What A260/A280 ratio is typically expected for pure RNA?

    Answer: ~2.0

    Pure RNA usually gives an A260/A280 ratio near 2.0.

  4. An A260 reading of 1.0 corresponds to approximately what concentration of double-stranded DNA?

    Answer: 50 µg/mL

    One A260 unit equals about 50 µg/mL dsDNA, 40 µg/mL RNA, and 33 µg/mL ssDNA.

  5. Why is fluorometric quantification (e.g., dye-based dsDNA assays) often preferred over UV absorbance for low-concentration samples?

    Answer: It is more sensitive and specific for dsDNA, unaffected by RNA or free nucleotides

    Fluorescent dyes bind specifically to dsDNA, giving accurate low-level quantification without interference from RNA or nucleotides.

  6. What does an RNA Integrity Number (RIN) of 9.5 indicate?

    Answer: Highly intact RNA suitable for RT-qPCR

    RIN ranges from 1 (fully degraded) to 10 (fully intact), so 9.5 indicates high-quality RNA.

  7. On a denaturing gel of intact eukaryotic total RNA, what 28S:18S rRNA band intensity ratio is expected?

    Answer: About 2:1

    Intact RNA shows a 28S band roughly twice as intense as the 18S band; degradation lowers this ratio and causes smearing.

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