BIO 411 MOLECULAR BIOLOGY
MIDTERM EXAM
DNA Replication Transcription Translation Gene Regulation Molecular
Techniques Questions and Answers Verified Solutions 2026 2027
1. Which chemical bond connects adjacent nucleotides along a single strand of a DNA
polymer?
A. Hydrogen bond
B. Peptide bond
C. Phosphodiester bond
D. Glycosidic bond
Rationale: Phosphodiester bonds join the 3' hydroxyl group of one deoxynucleotide to the 5' phosphate
group of another. Hydrogen bonds form between complementary bases across opposite strands, while
peptide bonds link amino acids in proteins.
2. During DNA replication in Escherichia coli, which enzyme unwinds the double helix at
the replication fork?
A. DNA Helicase (DnaB)
B. DNA Primase (DnaG)
C. DNA Topoisomerase (Gyrase)
D. DNA Polymerase I
Rationale: DnaB helicase breaks hydrogen bonds between nitrogenous bases to unwind the parental
strands. Primase synthesizes RNA primers, topoisomerase relieves torsional strain ahead of the fork, and
Polymerase I removes primers.
3. What is the primary function of Okazaki fragments during nucleic acid synthesis?
A. They initiate transcription at promoter sequences
B. They allow discontinuous synthesis on the lagging strand
C. They protect mRNA transcripts from enzymatic degradation
D. They anchor ribosomes to the endoplasmic reticulum
Rationale: DNA polymerase only synthesizes DNA in the 5' to 3' direction. Because the lagging strand
, template runs 5' to 3' relative to fork movement, synthesis occurs in short, discontinuous stretches called
Okazaki fragments.
4. Which eukaryotic DNA polymerase is primarily responsible for synthesizing the
lagging strand during nuclear DNA replication?
A. Polymerase alpha
B. Polymerase gamma
C. Polymerase delta
D. Polymerase epsilon
Rationale: Polymerase delta elongates Okazaki fragments on the lagging strand, whereas Polymerase
epsilon carries out continuous leading strand synthesis. Polymerase alpha lays down initial primers, and
gamma replicates mitochondrial DNA.
5. What enzyme prevents the progressive shortening of chromosome ends in eukaryotic
cells?
A. Telomerase
B. DNA Ligase
C. Reverse Transcriptase
D. Topoisomerase II
Rationale: Telomerase is a ribonucleoprotein reverse transcriptase that extends repetitive chromosome
ends using its internal RNA template. Ligase seals nicked backbone fragments, and topoisomerases
manage DNA supercoiling.
6. Which structural motif in prokaryotic promoters is located approximately 10 base pairs
upstream from the transcription start site?
A. CAAT box
B. Pribnow box (TATAAT)
C. GC box
D. Enhancer region
Rationale: The -10 region, or Pribnow box, consists of the consensus sequence TATAAT and aids in
unwinding DNA during transcription initiation in bacteria. CAAT and GC boxes are eukaryotic regulatory
elements.
7. What is the role of the sigma subunit in bacterial RNA polymerase holoenzyme?
MIDTERM EXAM
DNA Replication Transcription Translation Gene Regulation Molecular
Techniques Questions and Answers Verified Solutions 2026 2027
1. Which chemical bond connects adjacent nucleotides along a single strand of a DNA
polymer?
A. Hydrogen bond
B. Peptide bond
C. Phosphodiester bond
D. Glycosidic bond
Rationale: Phosphodiester bonds join the 3' hydroxyl group of one deoxynucleotide to the 5' phosphate
group of another. Hydrogen bonds form between complementary bases across opposite strands, while
peptide bonds link amino acids in proteins.
2. During DNA replication in Escherichia coli, which enzyme unwinds the double helix at
the replication fork?
A. DNA Helicase (DnaB)
B. DNA Primase (DnaG)
C. DNA Topoisomerase (Gyrase)
D. DNA Polymerase I
Rationale: DnaB helicase breaks hydrogen bonds between nitrogenous bases to unwind the parental
strands. Primase synthesizes RNA primers, topoisomerase relieves torsional strain ahead of the fork, and
Polymerase I removes primers.
3. What is the primary function of Okazaki fragments during nucleic acid synthesis?
A. They initiate transcription at promoter sequences
B. They allow discontinuous synthesis on the lagging strand
C. They protect mRNA transcripts from enzymatic degradation
D. They anchor ribosomes to the endoplasmic reticulum
Rationale: DNA polymerase only synthesizes DNA in the 5' to 3' direction. Because the lagging strand
, template runs 5' to 3' relative to fork movement, synthesis occurs in short, discontinuous stretches called
Okazaki fragments.
4. Which eukaryotic DNA polymerase is primarily responsible for synthesizing the
lagging strand during nuclear DNA replication?
A. Polymerase alpha
B. Polymerase gamma
C. Polymerase delta
D. Polymerase epsilon
Rationale: Polymerase delta elongates Okazaki fragments on the lagging strand, whereas Polymerase
epsilon carries out continuous leading strand synthesis. Polymerase alpha lays down initial primers, and
gamma replicates mitochondrial DNA.
5. What enzyme prevents the progressive shortening of chromosome ends in eukaryotic
cells?
A. Telomerase
B. DNA Ligase
C. Reverse Transcriptase
D. Topoisomerase II
Rationale: Telomerase is a ribonucleoprotein reverse transcriptase that extends repetitive chromosome
ends using its internal RNA template. Ligase seals nicked backbone fragments, and topoisomerases
manage DNA supercoiling.
6. Which structural motif in prokaryotic promoters is located approximately 10 base pairs
upstream from the transcription start site?
A. CAAT box
B. Pribnow box (TATAAT)
C. GC box
D. Enhancer region
Rationale: The -10 region, or Pribnow box, consists of the consensus sequence TATAAT and aids in
unwinding DNA during transcription initiation in bacteria. CAAT and GC boxes are eukaryotic regulatory
elements.
7. What is the role of the sigma subunit in bacterial RNA polymerase holoenzyme?
