BIOL 101 Exam 4 V1 | BIOL 101 Principles of Biology | Actual Q&A
with Rationale (BIOL101 Exam 4) | Liberty University
1. Which individual is credited with the discovery of the double-helical structure of DNA
based on X-ray diffraction data?
A. Charles Darwin
B. Gregor Mendel
C. James Watson and Francis Crick
D. Louis Pasteur
Correct Answer: C
Explanation: Watson and Crick utilized data from Rosalind Franklin to model the DNA
molecule. Their discovery provided the foundation for understanding how genetic
information is stored and copied. This structure involves two strands of nucleotides held
together by hydrogen bonds between complementary bases.
2. In the DNA molecule, which nitrogenous base always pairs with Cytosine?
A. Adenine
B. Thymine
C. Uracil
D. Guanine
Correct Answer: D
Explanation: According to Chargaff’s rules of base pairing, Guanine always forms three
hydrogen bonds with Cytosine. This specific pairing ensures the uniform width of the DNA
double helix. Adenine, by contrast, pairs with Thymine in DNA through two hydrogen
bonds.
3. DNA replication is described as ‘semiconservative’ because:
A. One strand is DNA and the other is RNA.
B. Each new DNA molecule consists of one original strand and one newly synthesized
strand.
C. The entire original molecule is kept intact while a new one is built.
D. The genetic code is conserved only in eukaryotic organisms.
Correct Answer: B
,Explanation: Semiconservative replication means that each parental strand serves as a
template for the synthesis of a new daughter strand. This process ensures that genetic
information is accurately passed from one cell generation to the next. Meselson and Stahl
provided the experimental evidence supporting this mechanism in the 1950s.
4. Which enzyme is responsible for adding nucleotides to the growing DNA strand during
replication?
A. Helicase
B. DNA Ligase
C. RNA Primase
D. DNA Polymerase
Correct Answer: D
Explanation: DNA Polymerase III is the primary enzyme that catalyzes the synthesis of
new DNA by adding nucleotides to the 3’ end of a primer. It also possesses proofreading
capabilities to correct errors during the replication process. Without this enzyme, the
elongation of the DNA chain would not occur.
5. The central dogma of molecular biology states that information flows in which sequence?
A. DNA to RNA to Protein
B. Protein to RNA to DNA
C. RNA to DNA to Protein
D. DNA to Protein to RNA
Correct Answer: A
Explanation: The central dogma describes the standard path for the expression of genetic
information within a cell. DNA is transcribed into messenger RNA, which is then translated
into a functional protein. This framework is universal across almost all living organisms,
though retroviruses provide a notable exception.
6. During transcription, the enzyme RNA polymerase binds to a specific DNA sequence called
the:
A. Terminator
B. Intron
C. Exon
D. Promoter
Correct Answer: D
, Explanation: The promoter acts as a signaling sequence that tells RNA polymerase where
to begin transcribing a gene. It determines which strand of DNA will be used as the
template. Transcription factors often assist RNA polymerase in recognizing and binding to
this site in eukaryotes.
7. What is the primary function of the ‘Poly-A tail’ added to eukaryotic mRNA?
A. It protects the mRNA from degradation and aids in export from the nucleus.
B. It codes for the start of translation.
C. It removes introns from the pre-mRNA sequence.
D. It serves as a binding site for the ribosome’s large subunit.
Correct Answer: A
Explanation: The Poly-A tail consists of many adenine nucleotides added to the 3’ end of
the mRNA transcript. This modification increases the stability of the molecule as it travels
through the cytoplasm. Furthermore, it facilitates the export of the mature mRNA through
the nuclear pore complex.
8. A sequence of three nucleotides on an mRNA molecule that codes for a specific amino acid
is known as a(n):
A. Anticodon
B. Codon
C. Promoter
D. Intron
Correct Answer: B
Explanation: A codon represents the basic unit of the genetic code, with 64 possible
combinations specifying 20 different amino acids. The sequence of codons in mRNA
determines the primary structure of the resulting polypeptide. Some codons also function
as start or stop signals for translation.
9. Which molecule carries the specific amino acid to the ribosome during translation?
A. tRNA
B. rRNA
C. mRNA
D. DNA
Correct Answer: A
Explanation: Transfer RNA (tRNA) acts as an adapter molecule that bridges the gap
between nucleic acids and proteins. Each tRNA has an anticodon that is complementary to
with Rationale (BIOL101 Exam 4) | Liberty University
1. Which individual is credited with the discovery of the double-helical structure of DNA
based on X-ray diffraction data?
A. Charles Darwin
B. Gregor Mendel
C. James Watson and Francis Crick
D. Louis Pasteur
Correct Answer: C
Explanation: Watson and Crick utilized data from Rosalind Franklin to model the DNA
molecule. Their discovery provided the foundation for understanding how genetic
information is stored and copied. This structure involves two strands of nucleotides held
together by hydrogen bonds between complementary bases.
2. In the DNA molecule, which nitrogenous base always pairs with Cytosine?
A. Adenine
B. Thymine
C. Uracil
D. Guanine
Correct Answer: D
Explanation: According to Chargaff’s rules of base pairing, Guanine always forms three
hydrogen bonds with Cytosine. This specific pairing ensures the uniform width of the DNA
double helix. Adenine, by contrast, pairs with Thymine in DNA through two hydrogen
bonds.
3. DNA replication is described as ‘semiconservative’ because:
A. One strand is DNA and the other is RNA.
B. Each new DNA molecule consists of one original strand and one newly synthesized
strand.
C. The entire original molecule is kept intact while a new one is built.
D. The genetic code is conserved only in eukaryotic organisms.
Correct Answer: B
,Explanation: Semiconservative replication means that each parental strand serves as a
template for the synthesis of a new daughter strand. This process ensures that genetic
information is accurately passed from one cell generation to the next. Meselson and Stahl
provided the experimental evidence supporting this mechanism in the 1950s.
4. Which enzyme is responsible for adding nucleotides to the growing DNA strand during
replication?
A. Helicase
B. DNA Ligase
C. RNA Primase
D. DNA Polymerase
Correct Answer: D
Explanation: DNA Polymerase III is the primary enzyme that catalyzes the synthesis of
new DNA by adding nucleotides to the 3’ end of a primer. It also possesses proofreading
capabilities to correct errors during the replication process. Without this enzyme, the
elongation of the DNA chain would not occur.
5. The central dogma of molecular biology states that information flows in which sequence?
A. DNA to RNA to Protein
B. Protein to RNA to DNA
C. RNA to DNA to Protein
D. DNA to Protein to RNA
Correct Answer: A
Explanation: The central dogma describes the standard path for the expression of genetic
information within a cell. DNA is transcribed into messenger RNA, which is then translated
into a functional protein. This framework is universal across almost all living organisms,
though retroviruses provide a notable exception.
6. During transcription, the enzyme RNA polymerase binds to a specific DNA sequence called
the:
A. Terminator
B. Intron
C. Exon
D. Promoter
Correct Answer: D
, Explanation: The promoter acts as a signaling sequence that tells RNA polymerase where
to begin transcribing a gene. It determines which strand of DNA will be used as the
template. Transcription factors often assist RNA polymerase in recognizing and binding to
this site in eukaryotes.
7. What is the primary function of the ‘Poly-A tail’ added to eukaryotic mRNA?
A. It protects the mRNA from degradation and aids in export from the nucleus.
B. It codes for the start of translation.
C. It removes introns from the pre-mRNA sequence.
D. It serves as a binding site for the ribosome’s large subunit.
Correct Answer: A
Explanation: The Poly-A tail consists of many adenine nucleotides added to the 3’ end of
the mRNA transcript. This modification increases the stability of the molecule as it travels
through the cytoplasm. Furthermore, it facilitates the export of the mature mRNA through
the nuclear pore complex.
8. A sequence of three nucleotides on an mRNA molecule that codes for a specific amino acid
is known as a(n):
A. Anticodon
B. Codon
C. Promoter
D. Intron
Correct Answer: B
Explanation: A codon represents the basic unit of the genetic code, with 64 possible
combinations specifying 20 different amino acids. The sequence of codons in mRNA
determines the primary structure of the resulting polypeptide. Some codons also function
as start or stop signals for translation.
9. Which molecule carries the specific amino acid to the ribosome during translation?
A. tRNA
B. rRNA
C. mRNA
D. DNA
Correct Answer: A
Explanation: Transfer RNA (tRNA) acts as an adapter molecule that bridges the gap
between nucleic acids and proteins. Each tRNA has an anticodon that is complementary to
