ASCP Molecular Biology Examination
Questions and Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which molecule stores hereditary information in most living organisms?
A. RNA
B. Protein
C. DNA
D. Lipid
Correct Answer: C. DNA
Rationale: DNA is the primary genetic material in nearly all organisms. RNA mainly
functions in gene expression, proteins perform cellular functions, and lipids form
membranes.
2. Which nitrogenous base is found in RNA but not in DNA?
A. Adenine
B. Cytosine
C. Guanine
D. Uracil
Correct Answer: D. Uracil
Rationale: Uracil replaces thymine in RNA. Adenine, cytosine, and guanine occur
in both DNA and RNA.
3. During DNA replication, which enzyme synthesizes the new DNA strand?
A. DNA ligase
B. Helicase
,C. DNA polymerase
D. Primase
Correct Answer: C. DNA polymerase
Rationale: DNA polymerase adds nucleotides to the growing DNA strand. Helicase
unwinds DNA, primase synthesizes RNA primers, and ligase seals DNA fragments.
4. What is the function of helicase during DNA replication?
A. Joins DNA fragments
B. Separates the DNA strands
C. Removes RNA primers
D. Repairs mutations
Correct Answer: B. Separates the DNA strands
Rationale: Helicase breaks hydrogen bonds between complementary bases,
allowing replication to begin.
5. Which enzyme joins Okazaki fragments?
A. DNA polymerase
B. Primase
C. Topoisomerase
D. DNA ligase
Correct Answer: D. DNA ligase
Rationale: DNA ligase seals breaks in the sugar-phosphate backbone between
adjacent DNA fragments.
6. PCR is primarily used to:
A. Translate proteins
B. Sequence DNA directly
,C. Amplify a DNA target
D. Separate chromosomes
Correct Answer: C. Amplify a DNA target
Rationale: PCR produces millions of copies of a selected DNA sequence.
7. Which PCR step separates double-stranded DNA?
A. Annealing
B. Extension
C. Denaturation
D. Hybridization
Correct Answer: C. Denaturation
Rationale: Denaturation uses heat to separate DNA strands before primer
binding.
8. During PCR, primers bind to DNA during which step?
A. Denaturation
B. Annealing
C. Extension
D. Elongation
Correct Answer: B. Annealing
Rationale: Annealing allows primers to hybridize to complementary DNA
sequences.
9. Which enzyme is commonly used in PCR because it tolerates high
temperatures?
A. DNA ligase
B. Reverse transcriptase
, C. RNA polymerase
D. Taq DNA polymerase
Correct Answer: D. Taq DNA polymerase
Rationale: Taq polymerase remains active after repeated heating cycles.
10. Reverse transcription converts:
A. DNA to protein
B. Protein to RNA
C. RNA to DNA
D. DNA to RNA
Correct Answer: C. RNA to DNA
Rationale: Reverse transcriptase synthesizes complementary DNA (cDNA) from an
RNA template.
11. Which technique is most commonly used to measure gene expression?
A. Southern blot
B. Western blot
C. RT-qPCR
D. Gram stain
Correct Answer: C. RT-qPCR
Rationale: RT-qPCR measures RNA expression by converting RNA into cDNA
followed by quantitative PCR.
12. Which instrument detects fluorescence during real-time PCR?
A. Centrifuge
B. Spectrophotometer only
C. Real-time PCR thermocycler
D. Incubator
Questions and Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which molecule stores hereditary information in most living organisms?
A. RNA
B. Protein
C. DNA
D. Lipid
Correct Answer: C. DNA
Rationale: DNA is the primary genetic material in nearly all organisms. RNA mainly
functions in gene expression, proteins perform cellular functions, and lipids form
membranes.
2. Which nitrogenous base is found in RNA but not in DNA?
A. Adenine
B. Cytosine
C. Guanine
D. Uracil
Correct Answer: D. Uracil
Rationale: Uracil replaces thymine in RNA. Adenine, cytosine, and guanine occur
in both DNA and RNA.
3. During DNA replication, which enzyme synthesizes the new DNA strand?
A. DNA ligase
B. Helicase
,C. DNA polymerase
D. Primase
Correct Answer: C. DNA polymerase
Rationale: DNA polymerase adds nucleotides to the growing DNA strand. Helicase
unwinds DNA, primase synthesizes RNA primers, and ligase seals DNA fragments.
4. What is the function of helicase during DNA replication?
A. Joins DNA fragments
B. Separates the DNA strands
C. Removes RNA primers
D. Repairs mutations
Correct Answer: B. Separates the DNA strands
Rationale: Helicase breaks hydrogen bonds between complementary bases,
allowing replication to begin.
5. Which enzyme joins Okazaki fragments?
A. DNA polymerase
B. Primase
C. Topoisomerase
D. DNA ligase
Correct Answer: D. DNA ligase
Rationale: DNA ligase seals breaks in the sugar-phosphate backbone between
adjacent DNA fragments.
6. PCR is primarily used to:
A. Translate proteins
B. Sequence DNA directly
,C. Amplify a DNA target
D. Separate chromosomes
Correct Answer: C. Amplify a DNA target
Rationale: PCR produces millions of copies of a selected DNA sequence.
7. Which PCR step separates double-stranded DNA?
A. Annealing
B. Extension
C. Denaturation
D. Hybridization
Correct Answer: C. Denaturation
Rationale: Denaturation uses heat to separate DNA strands before primer
binding.
8. During PCR, primers bind to DNA during which step?
A. Denaturation
B. Annealing
C. Extension
D. Elongation
Correct Answer: B. Annealing
Rationale: Annealing allows primers to hybridize to complementary DNA
sequences.
9. Which enzyme is commonly used in PCR because it tolerates high
temperatures?
A. DNA ligase
B. Reverse transcriptase
, C. RNA polymerase
D. Taq DNA polymerase
Correct Answer: D. Taq DNA polymerase
Rationale: Taq polymerase remains active after repeated heating cycles.
10. Reverse transcription converts:
A. DNA to protein
B. Protein to RNA
C. RNA to DNA
D. DNA to RNA
Correct Answer: C. RNA to DNA
Rationale: Reverse transcriptase synthesizes complementary DNA (cDNA) from an
RNA template.
11. Which technique is most commonly used to measure gene expression?
A. Southern blot
B. Western blot
C. RT-qPCR
D. Gram stain
Correct Answer: C. RT-qPCR
Rationale: RT-qPCR measures RNA expression by converting RNA into cDNA
followed by quantitative PCR.
12. Which instrument detects fluorescence during real-time PCR?
A. Centrifuge
B. Spectrophotometer only
C. Real-time PCR thermocycler
D. Incubator
