BIOL 101 Exam 3 V2 | BIOL 101 Principles of Biology | Actual Q&A
with Rationale (BIOL101 Exam 3) | Liberty University
1. Which component forms the repeating units of the DNA backbone?
A. Nitrogenous bases
B. Amino acids and peptides
C. Phosphate groups and deoxyribose sugars
D. Hydrogen bonds and lipids
Correct Answer: C
Explanation: The DNA backbone is constructed from alternating sugar and phosphate
molecules. These components are joined by covalent phosphodiester bonds to provide a
stable framework. The nitrogenous bases are attached to the sugars and extend into the
center of the helix.
2. According to Chargaff’s rules, which nitrogenous base always pairs with Guanine?
A. Adenine
B. Thymine
C. Uracil
D. Cytosine
Correct Answer: D
Explanation: Chargaff’s rules state that in a DNA molecule, the amount of guanine equals
the amount of cytosine. This occurs because guanine forms three hydrogen bonds
specifically with cytosine. These base-pairing rules ensure the uniform width of the DNA
double helix.
3. What enzyme is responsible for unwinding the DNA double helix during replication?
A. DNA Polymerase
B. Helicase
C. Ligase
D. RNA Polymerase
Correct Answer: B
Explanation: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases of the two strands. This action creates the replication fork where new
,DNA can be synthesized. Without helicase, the double helix would remain tightly coiled and
inaccessible to other enzymes.
4. In which direction does DNA Polymerase III synthesize a new DNA strand?
A. 3’ to 5’
B. 5’ to 3’ and 3’ to 5’ simultaneously
C. 5’ to 3’ only
D. Randomly based on availability
Correct Answer: C
Explanation: DNA Polymerase III can only add new nucleotides to the 3’ end of a pre-
existing strand. Consequently, the new strand is always synthesized in the 5’ to 3’ direction
relative to itself. This directional requirement leads to the formation of leading and lagging
strands.
5. What is the primary function of mRNA in a eukaryotic cell?
A. To catalyze the formation of peptide bonds
B. To transport amino acids to the site of translation
C. To carry genetic information from the nucleus to the ribosome
D. To provide structural support for the cell wall
Correct Answer: C
Explanation: Messenger RNA acts as an intermediate messenger that carries the genetic
code from the DNA in the nucleus to the cytoplasm. It serves as the template for protein
synthesis during the process of translation. Once in the cytoplasm, the mRNA interacts with
ribosomes to assemble amino acids.
6. During transcription, what is the role of the promoter region?
A. To signal the end of the gene sequence
B. To protect the mRNA from enzymatic degradation
C. To code for the start codon methionine
D. To provide a binding site for RNA polymerase to start transcription
Correct Answer: D
Explanation: The promoter is a specific sequence of DNA located upstream of the gene
being transcribed. It serves as the recognition and binding site for RNA polymerase and
transcription factors. The initiation of transcription depends entirely on the correct
recognition of this region.
, 7. Which of the following is a characteristic of RNA but not DNA?
A. Contains a deoxyribose sugar
B. Contains the nitrogenous base Uracil
C. Forms a double-stranded helix structure
D. Stores genetic information long-term
Correct Answer: B
Explanation: RNA uses uracil instead of the thymine found in DNA molecules. Additionally,
RNA is typically single-stranded and contains ribose sugar instead of deoxyribose. These
structural differences allow RNA to perform various roles in gene expression and
regulation.
8. What occurs during the process of RNA splicing in eukaryotes?
A. Exons are removed and introns are joined together
B. Introns are removed and exons are joined together
C. A poly-A tail is added to the 5’ end
D. Amino acids are attached to the tRNA molecule
Correct Answer: B
Explanation: RNA splicing involves the removal of non-coding regions called introns from
the primary transcript. The remaining coding regions, known as exons, are then spliced
together to form a mature mRNA. This process allows a single gene to potentially code for
multiple proteins through alternative splicing.
9. A codon consists of how many nucleotides?
A. One
B. Two
C. Four
D. Three
Correct Answer: D
Explanation: The genetic code is read in groups of three nucleotides known as codons.
Each codon specifies a particular amino acid or serves as a start or stop signal. This triplet
nature provides enough combinations to code for all twenty essential amino acids.
10. What is the function of the tRNA anticodon?
A. To base-pair with a specific mRNA codon
B. To carry the amino acid to the nucleus
with Rationale (BIOL101 Exam 3) | Liberty University
1. Which component forms the repeating units of the DNA backbone?
A. Nitrogenous bases
B. Amino acids and peptides
C. Phosphate groups and deoxyribose sugars
D. Hydrogen bonds and lipids
Correct Answer: C
Explanation: The DNA backbone is constructed from alternating sugar and phosphate
molecules. These components are joined by covalent phosphodiester bonds to provide a
stable framework. The nitrogenous bases are attached to the sugars and extend into the
center of the helix.
2. According to Chargaff’s rules, which nitrogenous base always pairs with Guanine?
A. Adenine
B. Thymine
C. Uracil
D. Cytosine
Correct Answer: D
Explanation: Chargaff’s rules state that in a DNA molecule, the amount of guanine equals
the amount of cytosine. This occurs because guanine forms three hydrogen bonds
specifically with cytosine. These base-pairing rules ensure the uniform width of the DNA
double helix.
3. What enzyme is responsible for unwinding the DNA double helix during replication?
A. DNA Polymerase
B. Helicase
C. Ligase
D. RNA Polymerase
Correct Answer: B
Explanation: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases of the two strands. This action creates the replication fork where new
,DNA can be synthesized. Without helicase, the double helix would remain tightly coiled and
inaccessible to other enzymes.
4. In which direction does DNA Polymerase III synthesize a new DNA strand?
A. 3’ to 5’
B. 5’ to 3’ and 3’ to 5’ simultaneously
C. 5’ to 3’ only
D. Randomly based on availability
Correct Answer: C
Explanation: DNA Polymerase III can only add new nucleotides to the 3’ end of a pre-
existing strand. Consequently, the new strand is always synthesized in the 5’ to 3’ direction
relative to itself. This directional requirement leads to the formation of leading and lagging
strands.
5. What is the primary function of mRNA in a eukaryotic cell?
A. To catalyze the formation of peptide bonds
B. To transport amino acids to the site of translation
C. To carry genetic information from the nucleus to the ribosome
D. To provide structural support for the cell wall
Correct Answer: C
Explanation: Messenger RNA acts as an intermediate messenger that carries the genetic
code from the DNA in the nucleus to the cytoplasm. It serves as the template for protein
synthesis during the process of translation. Once in the cytoplasm, the mRNA interacts with
ribosomes to assemble amino acids.
6. During transcription, what is the role of the promoter region?
A. To signal the end of the gene sequence
B. To protect the mRNA from enzymatic degradation
C. To code for the start codon methionine
D. To provide a binding site for RNA polymerase to start transcription
Correct Answer: D
Explanation: The promoter is a specific sequence of DNA located upstream of the gene
being transcribed. It serves as the recognition and binding site for RNA polymerase and
transcription factors. The initiation of transcription depends entirely on the correct
recognition of this region.
, 7. Which of the following is a characteristic of RNA but not DNA?
A. Contains a deoxyribose sugar
B. Contains the nitrogenous base Uracil
C. Forms a double-stranded helix structure
D. Stores genetic information long-term
Correct Answer: B
Explanation: RNA uses uracil instead of the thymine found in DNA molecules. Additionally,
RNA is typically single-stranded and contains ribose sugar instead of deoxyribose. These
structural differences allow RNA to perform various roles in gene expression and
regulation.
8. What occurs during the process of RNA splicing in eukaryotes?
A. Exons are removed and introns are joined together
B. Introns are removed and exons are joined together
C. A poly-A tail is added to the 5’ end
D. Amino acids are attached to the tRNA molecule
Correct Answer: B
Explanation: RNA splicing involves the removal of non-coding regions called introns from
the primary transcript. The remaining coding regions, known as exons, are then spliced
together to form a mature mRNA. This process allows a single gene to potentially code for
multiple proteins through alternative splicing.
9. A codon consists of how many nucleotides?
A. One
B. Two
C. Four
D. Three
Correct Answer: D
Explanation: The genetic code is read in groups of three nucleotides known as codons.
Each codon specifies a particular amino acid or serves as a start or stop signal. This triplet
nature provides enough combinations to code for all twenty essential amino acids.
10. What is the function of the tRNA anticodon?
A. To base-pair with a specific mRNA codon
B. To carry the amino acid to the nucleus
