Free Scientist in Molecular Biology - MB(ASCP) Practice Questions

Sample Practice Questions

Try these 10 sample questions from the Scientist in Molecular Biology - MB(ASCP) practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1Which sugar is part of an RNA nucleotide?

   1. A. Deoxyribose
   2. B. Ribose
   3. C. Glucose
   4. D. Fructose

   Answer: B

   Explanation: The NHGRI definition specifies "either ribose in RNA or deoxyribose in DNA". Therefore ribose is the sugar for an RNA nucleotide; deoxyribose belongs to DNA.

   Reference: NHGRI Talking Glossary: Nucleotide — Definition

2. 2In silica column purification, which condition promotes nucleic acid binding to the silica membrane?

   1. A. High chaotropic salt concentration
   2. B. Low salt elution buffer
   3. C. Proteinase K digestion alone
   4. D. RNase A digestion alone

   Answer: A

   Explanation: NEB states that "Nucleic acids bind to the silica membrane in the presence of chaotropic salts." Low salt is used later to elute; the enzymes serve different sample preparation roles.

   Reference: NEB: Silica Based Methods — Method description

3. 3For an open-tube molecular amplification workflow, in which direction should personnel and materials move to reduce amplicon carryover?

   1. A. From clean pre-amplification areas to post-amplification areas
   2. B. From product detection back to reagent preparation
   3. C. In either direction when negative controls are included
   4. D. From amplicon storage into specimen extraction

   Answer: A

   Explanation: CDC False-Positive Investigation Toolkit: Prevention Practices states "This practice ensures that work moves from clean (pre-amplification) to dirty (post- amplification) areas and decreases the potential for carryover or backflow contamination of amplicons." Thus from clean pre-amplification areas to post-amplification areas is the supported interpretation for this laboratory circumstance.

   Reference: CDC False-Positive Investigation Toolkit: Prevention Practices — Unidirectional workflow

4. 4A C. difficile PCR assay is positive in a patient without diarrhea or other compatible symptoms. What limits the result's interpretation?

   1. A. Molecular positivity can reflect colonization without infection
   2. B. Molecular positivity alone confirms symptomatic CDI
   3. C. Molecular positivity directly quantifies free stool toxin
   4. D. The result must be dismissed as assay contamination

   Answer: A

   Explanation: CDC Clinical Testing and Diagnosis for C. diff Infection states "Molecular assays can be positive for C. diff in asymptomatic individuals and those who do not have an infection." Therefore molecular positivity can reflect colonization without infection is supported for the stated clinical test.

   Reference: CDC Clinical Testing and Diagnosis for C. diff Infection — Recommended tests, Molecular tests

5. 5During RNA synthesis, which base takes the place of thymine in the nucleotide chain?

   1. A. Cytosine
   2. B. Guanine
   3. C. Uracil
   4. D. Adenine

   Answer: C

   Explanation: The NHGRI definition states, "In RNA, the base uracil (U) takes the place of thymine." The other listed bases occur in DNA as well.

   Reference: NHGRI Talking Glossary: Nucleotide — Definition

6. 6During silica column purification, which step removes residual proteins and salts while the nucleic acid remains bound?

   1. A. Alcohol-based washing
   2. B. Low-salt elution
   3. C. RNA transcription
   4. D. DNA ligation

   Answer: A

   Explanation: NEB explains that residual proteins and polysaccharides "are removed during alcohol-based wash steps, along with the salts." Elution releases nucleic acid rather than washing contaminants away.

   Reference: NEB: Silica Based Methods — Method description

7. 7In an amplification run, what problem is a no-template control intended to reveal?

   1. A. Contamination or background amplification without target template
   2. B. Loss of sensitivity from a low-copy patient specimen
   3. C. A mismatch between patient genotype and phenotype
   4. D. Incorrect interpretation of a positive patient result

   Answer: A

   Explanation: CDC Good Laboratory Practices for Molecular Genetic Testing states "inclusion of NTC samples in these procedures is essential for monitoring the test procedures and indicating whether measures taken to minimize cross-contamination are effective." Thus contamination or background amplification without target template is the supported interpretation for this laboratory circumstance.

   Reference: CDC Good Laboratory Practices for Molecular Genetic Testing — Unidirectional workflow for molecular amplification procedures

8. 8A laboratory receives stool for C. difficile PCR testing. What does a positive FDA-approved PCR result primarily indicate?

   1. A. Presence of a toxin-producing C. difficile organism
   2. B. A measured concentration of free toxin B
   3. C. A confirmed cause of every symptom in the patient
   4. D. The precise antibiotic susceptibility pattern

   Answer: A

   Explanation: CDC Clinical Testing and Diagnosis for C. diff Infection states "FDA-approved PCR assays are same-day tests that are highly sensitive and specific for the presence of a toxin-producing C. diff organism." Therefore presence of a toxin-producing c. difficile organism is supported for the stated clinical test.

   Reference: CDC Clinical Testing and Diagnosis for C. diff Infection — Recommended tests, Molecular tests

9. 9Which set of components makes up a nucleotide?

   1. A. Sugar, phosphate group, and nitrogenous base
   2. B. Sugar, amino acid, and nitrogenous base
   3. C. Phosphate group, amino acid, and nitrogenous base
   4. D. Sugar, phosphate group, and amino acid

   Answer: A

   Explanation: NHGRI describes a nucleotide as "a sugar molecule (either ribose in RNA or deoxyribose in DNA) attached to a phosphate group and a nitrogen-containing base." An amino acid is not one of these three components.

   Reference: NHGRI Talking Glossary: Nucleotide — Definition

10. 10After binding and washing a silica column, which condition is used to release the nucleic acid?

    1. A. High chaotropic salt
    2. B. Low-salt water or TE buffer
    3. C. Phenol in the organic phase
    4. D. Proteinase K in lysis buffer

    Answer: B

    Explanation: NEB states, "After binding and washing, nucleic acids are selectively eluted under low-salt conditions, using water or TE buffer." The other conditions relate to binding, phase separation, or lysis.

    Reference: NEB: Silica Based Methods — Method description