BIOL 101 Quiz 4 V2 | BIOL 101 Principles of
Biology | Actual Q&A with Rationale (BIOL101 Quiz
4) | Liberty University
1. Which scientist’s X-ray diffraction data was crucial for determining the double-helical
structure of DNA?
A. Rosalind Franklin
B. Francis Crick
C. Erwin Chargaff
D. James Watson
Correct Answer: A
Explanation: Rosalind Franklin produced the high-resolution X-ray diffraction images
known as Photo 51. These images provided the essential evidence regarding the helical
nature and dimensions of the DNA molecule. Although her contributions were often
overlooked at the time, modern biological science recognizes her work as foundational to
the discovery made by Watson and Crick.
2. What are the three components that make up a DNA nucleotide?
A. A nitrogenous base, a deoxyribose sugar, and a sulfate group
B. A nitrogenous base, a ribose sugar, and a phosphate group
C. An amino acid, a deoxyribose sugar, and a phosphate group
,D. A nitrogenous base, a deoxyribose sugar, and a phosphate group
Correct Answer: D
Explanation: DNA nucleotides are the building blocks of the genetic code, consisting of a
specific five-carbon sugar, a nitrogen-containing base, and a phosphate group. The
deoxyribose sugar distinguishes DNA from RNA, which contains ribose. These units link
together via phosphodiester bonds to form the backbone of the DNA strand.
3. According to Chargaff’s rules, which base pairing is always found in DNA?
A. Guanine pairs with Cytosine
B. Adenine pairs with Cytosine
C. Adenine pairs with Uracil
D. Thymine pairs with Guanine
Correct Answer: A
Explanation: Chargaff observed that the concentration of purines always equals the
concentration of pyrimidines in DNA. Specifically, Guanine always hydrogen bonds with
Cytosine using three hydrogen bonds. This complementary base pairing is essential for the
stability and replication of the genetic material.
4. During DNA replication, which enzyme is responsible for unwinding the double helix at the
replication fork?
A. DNA Polymerase
, B. DNA Ligase
C. Helicase
D. RNA Primase
Correct Answer: C
Explanation: Helicase acts as a molecular motor that moves along the DNA backbone to
separate the two strands. By breaking the hydrogen bonds between complementary bases,
it creates the replication fork necessary for other enzymes to access the template. This
energy-intensive process is fueled by the hydrolysis of ATP.
5. In which direction does DNA Polymerase synthesize the new DNA strand?
A. 5’ to 3’ direction
B. 3’ to 5’ direction
C. Amino to Carboxyl direction
D. Bidirectionally along one strand
Correct Answer: A
Explanation: DNA Polymerase can only add new nucleotides to the 3’ hydroxyl group of a
pre-existing strand. Consequently, synthesis always proceeds in the 5’ to 3’ direction
relative to the new strand being created. This biochemical constraint results in the
formation of leading and lagging strands during the replication process.
Biology | Actual Q&A with Rationale (BIOL101 Quiz
4) | Liberty University
1. Which scientist’s X-ray diffraction data was crucial for determining the double-helical
structure of DNA?
A. Rosalind Franklin
B. Francis Crick
C. Erwin Chargaff
D. James Watson
Correct Answer: A
Explanation: Rosalind Franklin produced the high-resolution X-ray diffraction images
known as Photo 51. These images provided the essential evidence regarding the helical
nature and dimensions of the DNA molecule. Although her contributions were often
overlooked at the time, modern biological science recognizes her work as foundational to
the discovery made by Watson and Crick.
2. What are the three components that make up a DNA nucleotide?
A. A nitrogenous base, a deoxyribose sugar, and a sulfate group
B. A nitrogenous base, a ribose sugar, and a phosphate group
C. An amino acid, a deoxyribose sugar, and a phosphate group
,D. A nitrogenous base, a deoxyribose sugar, and a phosphate group
Correct Answer: D
Explanation: DNA nucleotides are the building blocks of the genetic code, consisting of a
specific five-carbon sugar, a nitrogen-containing base, and a phosphate group. The
deoxyribose sugar distinguishes DNA from RNA, which contains ribose. These units link
together via phosphodiester bonds to form the backbone of the DNA strand.
3. According to Chargaff’s rules, which base pairing is always found in DNA?
A. Guanine pairs with Cytosine
B. Adenine pairs with Cytosine
C. Adenine pairs with Uracil
D. Thymine pairs with Guanine
Correct Answer: A
Explanation: Chargaff observed that the concentration of purines always equals the
concentration of pyrimidines in DNA. Specifically, Guanine always hydrogen bonds with
Cytosine using three hydrogen bonds. This complementary base pairing is essential for the
stability and replication of the genetic material.
4. During DNA replication, which enzyme is responsible for unwinding the double helix at the
replication fork?
A. DNA Polymerase
, B. DNA Ligase
C. Helicase
D. RNA Primase
Correct Answer: C
Explanation: Helicase acts as a molecular motor that moves along the DNA backbone to
separate the two strands. By breaking the hydrogen bonds between complementary bases,
it creates the replication fork necessary for other enzymes to access the template. This
energy-intensive process is fueled by the hydrolysis of ATP.
5. In which direction does DNA Polymerase synthesize the new DNA strand?
A. 5’ to 3’ direction
B. 3’ to 5’ direction
C. Amino to Carboxyl direction
D. Bidirectionally along one strand
Correct Answer: A
Explanation: DNA Polymerase can only add new nucleotides to the 3’ hydroxyl group of a
pre-existing strand. Consequently, synthesis always proceeds in the 5’ to 3’ direction
relative to the new strand being created. This biochemical constraint results in the
formation of leading and lagging strands during the replication process.
