ASCP MB MOLECULAR BIOLOGY EXAM | ALL
PRACTICE Q&A 2026/2027 | A+ GRADED |
COMPREHENSIVE EXAM GUIDE 2026&2027
1. A laboratory receives a DNA specimen for PCR analysis. Which component of a
standard PCR reaction provides the specificity that determines which region of DNA is
amplified?
A. Taq DNA polymerase
B. Deoxynucleoside triphosphates
C. Sequence-specific primers
D. Magnesium ions
Answer: C
The primers define the boundaries of the target sequence and provide the specificity for
amplification. DNA polymerase, nucleotides, and magnesium are necessary for the reaction
but do not determine the target region.
2. During PCR optimization, a technologist observes no amplification in the patient sample
but obtains an appropriate amplification product in the positive control. Which
explanation is most likely?
A. The thermocycler failed completely
B. The patient specimen contains no detectable target or contains an amplification inhibitor
C. The primers were completely degraded
D. The positive control was contaminated
Answer: B
A successful positive control demonstrates that the PCR system is functioning. Failure in only
the patient specimen suggests absence of target or specimen-specific inhibition.
3. Which enzyme is primarily responsible for extending a newly synthesized DNA strand
during PCR?
A. DNA ligase
B. Reverse transcriptase
C. RNA polymerase
D. Thermostable DNA polymerase
Answer: D
,A thermostable DNA polymerase extends primers by incorporating complementary
nucleotides during the extension phase of PCR.
4. Which PCR step separates double-stranded DNA into single strands?
A. Denaturation
B. Annealing
C. Extension
D. Ligation
Answer: A
Denaturation uses elevated temperature to disrupt hydrogen bonds between complementary
DNA strands, producing single-stranded templates.
5. A molecular laboratory wants to detect an RNA virus by PCR. Which preliminary step
is required?
A. DNA ligation
B. RNA methylation
C. Reverse transcription
D. Protein digestion
Answer: C
Reverse transcription converts RNA into complementary DNA, which can then serve as the
template for PCR amplification.
6. A technologist is preparing a PCR master mix. Why is magnesium concentration
carefully controlled?
A. Magnesium provides fluorescent detection
B. Magnesium acts as a cofactor for DNA polymerase
C. Magnesium replaces the DNA template
D. Magnesium prevents primer synthesis
Answer: B
Magnesium ions are essential cofactors for DNA polymerase activity and influence primer
binding, amplification efficiency, and specificity.
,7. Which characteristic is most desirable when designing PCR primers?
A. Extensive complementarity between the two primers
B. Strong complementarity at their 3′ ends
C. Similar melting temperatures with minimal self-complementarity
D. Extremely high GC content in every primer
Answer: C
Primers with similar melting temperatures and minimal self-complementarity promote
efficient and specific amplification while reducing primer-dimer formation.
8. A PCR assay produces several unexpected bands on agarose gel electrophoresis. Which
optimization is most appropriate initially?
A. Increase nonspecific primer binding
B. Optimize the annealing temperature
C. Remove the DNA template
D. Eliminate all nucleotides
Answer: B
An inappropriate annealing temperature can permit nonspecific primer binding. Optimizing
this temperature is a common strategy for improving PCR specificity.
9. Which technique separates DNA fragments primarily according to size?
A. Agarose gel electrophoresis
B. Western blotting
C. ELISA
D. Flow cytometry
Answer: A
DNA fragments migrate through agarose in an electric field, with smaller fragments generally
moving faster and farther than larger fragments.
10. In agarose gel electrophoresis, DNA migrates toward the positive electrode because
DNA is:
A. Positively charged
B. Electrically neutral
C. Negatively charged
D. Hydrophobic
, Answer: C
The phosphate backbone gives DNA an overall negative charge, causing it to migrate toward
the positive electrode during electrophoresis.
11. Which reagent is commonly used to visualize DNA following electrophoresis?
A. Hematoxylin
B. A DNA-binding fluorescent dye
C. Coomassie blue only
D. Crystal violet only
Answer: B
DNA-binding fluorescent dyes allow separated DNA fragments to be visualized under an
appropriate detection system.
12. A molecular technologist needs to determine the exact nucleotide sequence of a short
PCR product. Which method is most appropriate?
A. Gram staining
B. Sanger sequencing
C. Western blotting
D. Nephelometry
Answer: B
Sanger sequencing is well suited for determining the nucleotide sequence of a defined DNA
fragment, particularly relatively short targets.
13. In Sanger sequencing, chain termination occurs because the reaction contains:
A. Ribosomal RNA
B. Modified dNTPs lacking a 3′-OH group
C. Excess RNA primers
D. Restriction enzymes
Answer: B
Dideoxynucleotides lack the 3′-OH required for continued phosphodiester bond formation,
causing termination when incorporated.
PRACTICE Q&A 2026/2027 | A+ GRADED |
COMPREHENSIVE EXAM GUIDE 2026&2027
1. A laboratory receives a DNA specimen for PCR analysis. Which component of a
standard PCR reaction provides the specificity that determines which region of DNA is
amplified?
A. Taq DNA polymerase
B. Deoxynucleoside triphosphates
C. Sequence-specific primers
D. Magnesium ions
Answer: C
The primers define the boundaries of the target sequence and provide the specificity for
amplification. DNA polymerase, nucleotides, and magnesium are necessary for the reaction
but do not determine the target region.
2. During PCR optimization, a technologist observes no amplification in the patient sample
but obtains an appropriate amplification product in the positive control. Which
explanation is most likely?
A. The thermocycler failed completely
B. The patient specimen contains no detectable target or contains an amplification inhibitor
C. The primers were completely degraded
D. The positive control was contaminated
Answer: B
A successful positive control demonstrates that the PCR system is functioning. Failure in only
the patient specimen suggests absence of target or specimen-specific inhibition.
3. Which enzyme is primarily responsible for extending a newly synthesized DNA strand
during PCR?
A. DNA ligase
B. Reverse transcriptase
C. RNA polymerase
D. Thermostable DNA polymerase
Answer: D
,A thermostable DNA polymerase extends primers by incorporating complementary
nucleotides during the extension phase of PCR.
4. Which PCR step separates double-stranded DNA into single strands?
A. Denaturation
B. Annealing
C. Extension
D. Ligation
Answer: A
Denaturation uses elevated temperature to disrupt hydrogen bonds between complementary
DNA strands, producing single-stranded templates.
5. A molecular laboratory wants to detect an RNA virus by PCR. Which preliminary step
is required?
A. DNA ligation
B. RNA methylation
C. Reverse transcription
D. Protein digestion
Answer: C
Reverse transcription converts RNA into complementary DNA, which can then serve as the
template for PCR amplification.
6. A technologist is preparing a PCR master mix. Why is magnesium concentration
carefully controlled?
A. Magnesium provides fluorescent detection
B. Magnesium acts as a cofactor for DNA polymerase
C. Magnesium replaces the DNA template
D. Magnesium prevents primer synthesis
Answer: B
Magnesium ions are essential cofactors for DNA polymerase activity and influence primer
binding, amplification efficiency, and specificity.
,7. Which characteristic is most desirable when designing PCR primers?
A. Extensive complementarity between the two primers
B. Strong complementarity at their 3′ ends
C. Similar melting temperatures with minimal self-complementarity
D. Extremely high GC content in every primer
Answer: C
Primers with similar melting temperatures and minimal self-complementarity promote
efficient and specific amplification while reducing primer-dimer formation.
8. A PCR assay produces several unexpected bands on agarose gel electrophoresis. Which
optimization is most appropriate initially?
A. Increase nonspecific primer binding
B. Optimize the annealing temperature
C. Remove the DNA template
D. Eliminate all nucleotides
Answer: B
An inappropriate annealing temperature can permit nonspecific primer binding. Optimizing
this temperature is a common strategy for improving PCR specificity.
9. Which technique separates DNA fragments primarily according to size?
A. Agarose gel electrophoresis
B. Western blotting
C. ELISA
D. Flow cytometry
Answer: A
DNA fragments migrate through agarose in an electric field, with smaller fragments generally
moving faster and farther than larger fragments.
10. In agarose gel electrophoresis, DNA migrates toward the positive electrode because
DNA is:
A. Positively charged
B. Electrically neutral
C. Negatively charged
D. Hydrophobic
, Answer: C
The phosphate backbone gives DNA an overall negative charge, causing it to migrate toward
the positive electrode during electrophoresis.
11. Which reagent is commonly used to visualize DNA following electrophoresis?
A. Hematoxylin
B. A DNA-binding fluorescent dye
C. Coomassie blue only
D. Crystal violet only
Answer: B
DNA-binding fluorescent dyes allow separated DNA fragments to be visualized under an
appropriate detection system.
12. A molecular technologist needs to determine the exact nucleotide sequence of a short
PCR product. Which method is most appropriate?
A. Gram staining
B. Sanger sequencing
C. Western blotting
D. Nephelometry
Answer: B
Sanger sequencing is well suited for determining the nucleotide sequence of a defined DNA
fragment, particularly relatively short targets.
13. In Sanger sequencing, chain termination occurs because the reaction contains:
A. Ribosomal RNA
B. Modified dNTPs lacking a 3′-OH group
C. Excess RNA primers
D. Restriction enzymes
Answer: B
Dideoxynucleotides lack the 3′-OH required for continued phosphodiester bond formation,
causing termination when incorporated.
