Bio 101 Exam 3 Study Guide Questions & Correct
Answers with Detailed Rationales | New 2026–2027
Update
Which of the following help(s) to hold the DNA strands apart while they are being
replicated?
A. single-strand binding proteins
B. DNA ligase
C. primase
D. helicase
Correct Answer: A
Expert Rationale: Single-strand binding proteins stabilize separated DNA strands
during replication.
A particular triplet of bases in the template strand of DNA is 5'-AGT-3'. The
corresponding codon for the mRNA transcribed is
A. 3'-UCA-5'
B. 5'-UCA-3'
C. 3'-TCA-5'
D. 5'-AGU-3'
Correct Answer: A
Expert Rationale: mRNA is complementary and antiparallel to the template
strand.
,What is the role of DNA ligase in the elongation of the lagging strand during DNA
replication?
A. It joins Okazaki fragments together.
B. It adds nucleotides to the 3' end.
C. It unwinds the double helix.
D. It synthesizes RNA primers.
Correct Answer: A
Expert Rationale: DNA ligase seals nicks between Okazaki fragments.
Which of the following sets of materials is required by both eukaryotes and
prokaryotes for DNA replication?
A. double-stranded DNA, four kinds of DNA nucleotides, primers, origins of
replication
B. single-stranded DNA, RNA nucleotides, no primers, no origins
C. double-stranded RNA, four kinds of RNA nucleotides, primers, origins
D. proteins only, no DNA, no nucleotides
Correct Answer: A
Expert Rationale: Both cell types need DNA template, nucleotides, primers, and
origins.
The term "gene expression" refers to the
A. process by which genetic information flows from genes to proteins.
B. process of DNA replication.
C. process of cell division.
D. process of mutation.
Correct Answer: A
, Expert Rationale: Gene expression is the flow of genetic information to functional
products.
Which of the following statements best describes the termination of transcription
in prokaryotes?
A. RNA polymerase transcribes through the terminator sequence, causing the
polymerase to separate from the DNA and release the transcript.
B. Ribosomes bind to the terminator and stop transcription.
C. DNA ligase cuts the RNA transcript.
D. Transcription stops when the cell runs out of ATP.
Correct Answer: A
Expert Rationale: Prokaryotic transcription ends at terminator sequences.
When the two subunits of ribosomes come together to translate the mRNA, what
sites are created for tRNAs?
A. A, E and P sites
B. A, B and C sites
C. X, Y and Z sites
D. 1, 2 and 3 sites
Correct Answer: A
Expert Rationale: Ribosomes have A, P, and E sites for tRNA binding.
A new DNA strand elongates only in the 5' to 3' direction because
A. DNA polymerase can only add nucleotides to the free 3' end.
B. DNA polymerase can only add nucleotides to the free 5' end.
C. DNA ligase adds nucleotides to the 5' end.
Answers with Detailed Rationales | New 2026–2027
Update
Which of the following help(s) to hold the DNA strands apart while they are being
replicated?
A. single-strand binding proteins
B. DNA ligase
C. primase
D. helicase
Correct Answer: A
Expert Rationale: Single-strand binding proteins stabilize separated DNA strands
during replication.
A particular triplet of bases in the template strand of DNA is 5'-AGT-3'. The
corresponding codon for the mRNA transcribed is
A. 3'-UCA-5'
B. 5'-UCA-3'
C. 3'-TCA-5'
D. 5'-AGU-3'
Correct Answer: A
Expert Rationale: mRNA is complementary and antiparallel to the template
strand.
,What is the role of DNA ligase in the elongation of the lagging strand during DNA
replication?
A. It joins Okazaki fragments together.
B. It adds nucleotides to the 3' end.
C. It unwinds the double helix.
D. It synthesizes RNA primers.
Correct Answer: A
Expert Rationale: DNA ligase seals nicks between Okazaki fragments.
Which of the following sets of materials is required by both eukaryotes and
prokaryotes for DNA replication?
A. double-stranded DNA, four kinds of DNA nucleotides, primers, origins of
replication
B. single-stranded DNA, RNA nucleotides, no primers, no origins
C. double-stranded RNA, four kinds of RNA nucleotides, primers, origins
D. proteins only, no DNA, no nucleotides
Correct Answer: A
Expert Rationale: Both cell types need DNA template, nucleotides, primers, and
origins.
The term "gene expression" refers to the
A. process by which genetic information flows from genes to proteins.
B. process of DNA replication.
C. process of cell division.
D. process of mutation.
Correct Answer: A
, Expert Rationale: Gene expression is the flow of genetic information to functional
products.
Which of the following statements best describes the termination of transcription
in prokaryotes?
A. RNA polymerase transcribes through the terminator sequence, causing the
polymerase to separate from the DNA and release the transcript.
B. Ribosomes bind to the terminator and stop transcription.
C. DNA ligase cuts the RNA transcript.
D. Transcription stops when the cell runs out of ATP.
Correct Answer: A
Expert Rationale: Prokaryotic transcription ends at terminator sequences.
When the two subunits of ribosomes come together to translate the mRNA, what
sites are created for tRNAs?
A. A, E and P sites
B. A, B and C sites
C. X, Y and Z sites
D. 1, 2 and 3 sites
Correct Answer: A
Expert Rationale: Ribosomes have A, P, and E sites for tRNA binding.
A new DNA strand elongates only in the 5' to 3' direction because
A. DNA polymerase can only add nucleotides to the free 3' end.
B. DNA polymerase can only add nucleotides to the free 5' end.
C. DNA ligase adds nucleotides to the 5' end.
