BSC 108 Exam 3 (Kennedy), 2026/2027 –
Cellular Energy, Genetics and Molecular
Biology Competency Assessment
Section 1: DNA Structure, Composition, and
Replication (Questions 1-18)
Question 1: Which of the following correctly describes the structure of a
strand of DNA?
A. A single strand of nucleotides linked by hydrogen bonds
B. A double helix resembling a twisted ladder with nucleotide subunits
C. A triple helix with amino acid subunits
D. A branched chain of glucose molecules
Correct Answer: B. A double helix resembling a twisted ladder with
nucleotide subunits
Rationale: DNA is structured as a double helix, often compared to a twisted
ladder. The "rungs" of the ladder are formed by paired nucleotide bases
(adenine, thymine, cytosine, guanine), while the sides are formed by
covalent bonds in the sugar-phosphate backbone (composed of deoxyribose
and phosphate groups) .
Subtopic: DNA Structure
Question 2: What are the four nucleotide subunits found in DNA?
A. Adenine, uracil, cytosine, guanine
B. Adenine, thymine, cytosine, guanine
C. Ribose, adenine, thymine, phosphate
D. Alanine, thiamine, cysteine, glycine
Correct Answer: B. Adenine, thymine, cytosine, guanine
,Rationale: DNA contains four nitrogenous bases: adenine (A), thymine (T),
cytosine (C), and guanine (G). RNA uses uracil (U) instead of thymine, which
is a key distinction between the two nucleic acids .
Subtopic: DNA Structure - Nitrogenous Bases
Question 3: How are the nucleotide subunits held together within a DNA
strand?
A. Hydrogen bonds between sugars
B. Covalent bonds between sugar and phosphate groups
C. Ionic bonds between base pairs
D. Peptide bonds between amino acids
Correct Answer: B. Covalent bonds between sugar and phosphate groups
Rationale: Nucleotides are linked together by covalent bonds
(phosphodiester bonds) between the deoxyribose sugar of one nucleotide
and the phosphate group of the next. The two DNA strands are held together
by hydrogen bonds between complementary bases .
Subtopic: DNA Structure - Chemical Bonds
Question 4: Which of the following represents the correct complementary
base pairing in DNA?
A. Adenine pairs with guanine; cytosine pairs with thymine
B. Adenine pairs with thymine; cytosine pairs with guanine
C. Adenine pairs with uracil; cytosine pairs with guanine
D. Adenine pairs with adenine; cytosine pairs with cytosine
Correct Answer: B. Adenine pairs with thymine; cytosine pairs with guanine
Rationale: In DNA, complementary base pairing follows specific rules: A
(adenine) always pairs with T (thymine) via two hydrogen bonds, and C
(cytosine) always pairs with G (guanine) via three hydrogen bonds. This
pairing is essential for DNA replication and transcription .
Subtopic: DNA Structure - Base Pairing
Question 5: How many strands does a DNA molecule contain?
A. One strand
B. Two strands
C. Three strands
D. Four strands
Correct Answer: B. Two strands
, Rationale: The DNA molecule is double-stranded, forming the characteristic
double helix structure. These two strands are complementary to each other
and are held together by hydrogen bonds between base pairs .
Subtopic: DNA Structure - Double Helix
Question 6: The two strands of DNA are described as:
A. Identical
B. Complementary
C. Unrelated
D. Opposite in all ways
Correct Answer: B. Complementary
Rationale: The two DNA strands are complementary, meaning the sequence
of bases on one strand determines the sequence on the other through base-
pairing rules (A pairs with T, C pairs with G). This complementarity is
essential for DNA replication and transcription .
Subtopic: DNA Structure - Complementarity
Question 7: What is the function of the sugar-phosphate backbone in DNA?
A. To store genetic information through base sequences
B. To provide structural support and stability to the DNA molecule
C. To catalyze replication reactions
D. To code for protein sequences directly
Correct Answer: B. To provide structural support and stability to the DNA
molecule
Rationale: The sugar-phosphate backbone forms the structural framework of
DNA, with deoxyribose sugars and phosphate groups linked by covalent
bonds. While the backbone provides stability, the genetic information is
encoded in the sequence of nitrogenous bases attached to the backbone .
Subtopic: DNA Structure - Sugar-Phosphate Backbone
Question 8: How does DNA replicate?
A. The DNA molecule unwinds, and each strand serves as a template for
complementary base pairing
B. The DNA molecule remains intact while new DNA is synthesized elsewhere
C. The DNA molecule is completely broken down and reassembled
D. RNA serves as a template for new DNA synthesis
Correct Answer: A. The DNA molecule unwinds, and each strand serves as a
template for complementary base pairing
Cellular Energy, Genetics and Molecular
Biology Competency Assessment
Section 1: DNA Structure, Composition, and
Replication (Questions 1-18)
Question 1: Which of the following correctly describes the structure of a
strand of DNA?
A. A single strand of nucleotides linked by hydrogen bonds
B. A double helix resembling a twisted ladder with nucleotide subunits
C. A triple helix with amino acid subunits
D. A branched chain of glucose molecules
Correct Answer: B. A double helix resembling a twisted ladder with
nucleotide subunits
Rationale: DNA is structured as a double helix, often compared to a twisted
ladder. The "rungs" of the ladder are formed by paired nucleotide bases
(adenine, thymine, cytosine, guanine), while the sides are formed by
covalent bonds in the sugar-phosphate backbone (composed of deoxyribose
and phosphate groups) .
Subtopic: DNA Structure
Question 2: What are the four nucleotide subunits found in DNA?
A. Adenine, uracil, cytosine, guanine
B. Adenine, thymine, cytosine, guanine
C. Ribose, adenine, thymine, phosphate
D. Alanine, thiamine, cysteine, glycine
Correct Answer: B. Adenine, thymine, cytosine, guanine
,Rationale: DNA contains four nitrogenous bases: adenine (A), thymine (T),
cytosine (C), and guanine (G). RNA uses uracil (U) instead of thymine, which
is a key distinction between the two nucleic acids .
Subtopic: DNA Structure - Nitrogenous Bases
Question 3: How are the nucleotide subunits held together within a DNA
strand?
A. Hydrogen bonds between sugars
B. Covalent bonds between sugar and phosphate groups
C. Ionic bonds between base pairs
D. Peptide bonds between amino acids
Correct Answer: B. Covalent bonds between sugar and phosphate groups
Rationale: Nucleotides are linked together by covalent bonds
(phosphodiester bonds) between the deoxyribose sugar of one nucleotide
and the phosphate group of the next. The two DNA strands are held together
by hydrogen bonds between complementary bases .
Subtopic: DNA Structure - Chemical Bonds
Question 4: Which of the following represents the correct complementary
base pairing in DNA?
A. Adenine pairs with guanine; cytosine pairs with thymine
B. Adenine pairs with thymine; cytosine pairs with guanine
C. Adenine pairs with uracil; cytosine pairs with guanine
D. Adenine pairs with adenine; cytosine pairs with cytosine
Correct Answer: B. Adenine pairs with thymine; cytosine pairs with guanine
Rationale: In DNA, complementary base pairing follows specific rules: A
(adenine) always pairs with T (thymine) via two hydrogen bonds, and C
(cytosine) always pairs with G (guanine) via three hydrogen bonds. This
pairing is essential for DNA replication and transcription .
Subtopic: DNA Structure - Base Pairing
Question 5: How many strands does a DNA molecule contain?
A. One strand
B. Two strands
C. Three strands
D. Four strands
Correct Answer: B. Two strands
, Rationale: The DNA molecule is double-stranded, forming the characteristic
double helix structure. These two strands are complementary to each other
and are held together by hydrogen bonds between base pairs .
Subtopic: DNA Structure - Double Helix
Question 6: The two strands of DNA are described as:
A. Identical
B. Complementary
C. Unrelated
D. Opposite in all ways
Correct Answer: B. Complementary
Rationale: The two DNA strands are complementary, meaning the sequence
of bases on one strand determines the sequence on the other through base-
pairing rules (A pairs with T, C pairs with G). This complementarity is
essential for DNA replication and transcription .
Subtopic: DNA Structure - Complementarity
Question 7: What is the function of the sugar-phosphate backbone in DNA?
A. To store genetic information through base sequences
B. To provide structural support and stability to the DNA molecule
C. To catalyze replication reactions
D. To code for protein sequences directly
Correct Answer: B. To provide structural support and stability to the DNA
molecule
Rationale: The sugar-phosphate backbone forms the structural framework of
DNA, with deoxyribose sugars and phosphate groups linked by covalent
bonds. While the backbone provides stability, the genetic information is
encoded in the sequence of nitrogenous bases attached to the backbone .
Subtopic: DNA Structure - Sugar-Phosphate Backbone
Question 8: How does DNA replicate?
A. The DNA molecule unwinds, and each strand serves as a template for
complementary base pairing
B. The DNA molecule remains intact while new DNA is synthesized elsewhere
C. The DNA molecule is completely broken down and reassembled
D. RNA serves as a template for new DNA synthesis
Correct Answer: A. The DNA molecule unwinds, and each strand serves as a
template for complementary base pairing
