BIOL 101 Exam 4 V2 | BIOL 101 Principles of Biology | Actual Q&A
with Rationale (BIOL101 Exam 4) | Liberty University
1. Which of the following best describes the process of DNA replication?
A. Conservative replication
B. Dispersive replication
C. Semi-conservative replication
D. Continuous replication
Correct Answer: C
Explanation: DNA replication is considered semi-conservative because each new double
helix consists of one original strand and one newly synthesized strand. This mechanism
was famously demonstrated by the Meselson-Stahl experiment using nitrogen isotopes.
The process ensures that the genetic information is accurately preserved and passed on to
daughter cells.
2. During translation, which molecule carries the specific amino acid to the ribosome?
A. mRNA
B. DNA polymerase
C. rRNA
D. tRNA
Correct Answer: D
Explanation: Transfer RNA (tRNA) acts as an adapter molecule that links mRNA codons to
their corresponding amino acids. Each tRNA has an anticodon that base-pairs with a
specific mRNA codon, ensuring the correct amino acid is added to the growing polypeptide
chain. This specificity is crucial for the primary structure of the protein being synthesized.
3. What is the ‘Central Dogma’ of molecular biology?
A. RNA -> DNA -> Protein
B. DNA -> RNA -> Protein
C. Protein -> RNA -> DNA
D. DNA -> Protein -> RNA
Correct Answer: B
,Explanation: The Central Dogma describes the two-step process, transcription and
translation, by which the information in genes flows into proteins. Transcription converts
DNA into messenger RNA, and translation converts that mRNA into a functional protein.
This fundamental principle governs biological inheritance and expression in all living
organisms.
4. Which enzyme is responsible for unwinding the DNA double helix during replication?
A. DNA Polymerase
B. Ligase
C. Helicase
D. Primase
Correct Answer: C
Explanation: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases of the two DNA strands. This action creates a replication fork where the
individual strands can serve as templates for new DNA. Without helicase, the replication
machinery would not be able to access the genetic code embedded within the helix.
5. In a Mendelian monohybrid cross between two heterozygous (Aa) individuals, what is the
expected phenotypic ratio?
A. 1:2:1
B. 9:3:3:1
C. 3:1
D. 1:1
Correct Answer: C
Explanation: A 3:1 ratio occurs because there are three possible genotypes (AA, Aa, aA)
that result in the dominant phenotype and only one (aa) that results in the recessive
phenotype. This assumes complete dominance where the presence of one dominant allele
masks the recessive one. Gregor Mendel established this ratio through his extensive work
with pea plants.
6. Which type of mutation occurs when a single nucleotide is replaced by another, potentially
changing one amino acid?
A. Frameshift mutation
B. Missense mutation
C. Silent mutation
D. Nonsense mutation
, Correct Answer: B
Explanation: A missense mutation is a type of point mutation where a change in a single
DNA base pair results in the substitution of one amino acid for another in the protein. This
can range from having no effect to significantly altering the protein’s function, as seen in
sickle cell anemia. It differs from a nonsense mutation, which creates a premature stop
codon.
7. What is the primary function of the PCR (Polymerase Chain Reaction) technique?
A. To sequence an entire genome
B. To create recombinant DNA
C. To amplify specific segments of DNA
D. To visualize proteins on a gel
Correct Answer: C
Explanation: PCR allows scientists to take a very small sample of DNA and amplify a
specific region to billions of copies in a matter of hours. This technique relies on thermal
cycling, consisting of cycles of repeated heating and cooling for DNA melting and enzymatic
replication of the DNA. It has revolutionized forensic science, medical diagnostics, and
biological research.
8. Which nitrogenous base is found in RNA but not in DNA?
A. Uracil
B. Thymine
C. Adenine
D. Guanine
Correct Answer: A
Explanation: In RNA, the pyrimidine base uracil replaces thymine, which is found in DNA.
Uracil pairs with adenine through two hydrogen bonds, similar to how thymine pairs with
adenine. This chemical difference helps cellular machinery distinguish between DNA for
storage and RNA for temporary messaging and catalysis.
9. What characterizes a recessive allele?
A. It is always the most common allele in a population.
B. It masks the expression of a dominant allele.
C. Its phenotype is expressed only when two copies are present.
D. It is always harmful to the organism.
Correct Answer: C
with Rationale (BIOL101 Exam 4) | Liberty University
1. Which of the following best describes the process of DNA replication?
A. Conservative replication
B. Dispersive replication
C. Semi-conservative replication
D. Continuous replication
Correct Answer: C
Explanation: DNA replication is considered semi-conservative because each new double
helix consists of one original strand and one newly synthesized strand. This mechanism
was famously demonstrated by the Meselson-Stahl experiment using nitrogen isotopes.
The process ensures that the genetic information is accurately preserved and passed on to
daughter cells.
2. During translation, which molecule carries the specific amino acid to the ribosome?
A. mRNA
B. DNA polymerase
C. rRNA
D. tRNA
Correct Answer: D
Explanation: Transfer RNA (tRNA) acts as an adapter molecule that links mRNA codons to
their corresponding amino acids. Each tRNA has an anticodon that base-pairs with a
specific mRNA codon, ensuring the correct amino acid is added to the growing polypeptide
chain. This specificity is crucial for the primary structure of the protein being synthesized.
3. What is the ‘Central Dogma’ of molecular biology?
A. RNA -> DNA -> Protein
B. DNA -> RNA -> Protein
C. Protein -> RNA -> DNA
D. DNA -> Protein -> RNA
Correct Answer: B
,Explanation: The Central Dogma describes the two-step process, transcription and
translation, by which the information in genes flows into proteins. Transcription converts
DNA into messenger RNA, and translation converts that mRNA into a functional protein.
This fundamental principle governs biological inheritance and expression in all living
organisms.
4. Which enzyme is responsible for unwinding the DNA double helix during replication?
A. DNA Polymerase
B. Ligase
C. Helicase
D. Primase
Correct Answer: C
Explanation: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases of the two DNA strands. This action creates a replication fork where the
individual strands can serve as templates for new DNA. Without helicase, the replication
machinery would not be able to access the genetic code embedded within the helix.
5. In a Mendelian monohybrid cross between two heterozygous (Aa) individuals, what is the
expected phenotypic ratio?
A. 1:2:1
B. 9:3:3:1
C. 3:1
D. 1:1
Correct Answer: C
Explanation: A 3:1 ratio occurs because there are three possible genotypes (AA, Aa, aA)
that result in the dominant phenotype and only one (aa) that results in the recessive
phenotype. This assumes complete dominance where the presence of one dominant allele
masks the recessive one. Gregor Mendel established this ratio through his extensive work
with pea plants.
6. Which type of mutation occurs when a single nucleotide is replaced by another, potentially
changing one amino acid?
A. Frameshift mutation
B. Missense mutation
C. Silent mutation
D. Nonsense mutation
, Correct Answer: B
Explanation: A missense mutation is a type of point mutation where a change in a single
DNA base pair results in the substitution of one amino acid for another in the protein. This
can range from having no effect to significantly altering the protein’s function, as seen in
sickle cell anemia. It differs from a nonsense mutation, which creates a premature stop
codon.
7. What is the primary function of the PCR (Polymerase Chain Reaction) technique?
A. To sequence an entire genome
B. To create recombinant DNA
C. To amplify specific segments of DNA
D. To visualize proteins on a gel
Correct Answer: C
Explanation: PCR allows scientists to take a very small sample of DNA and amplify a
specific region to billions of copies in a matter of hours. This technique relies on thermal
cycling, consisting of cycles of repeated heating and cooling for DNA melting and enzymatic
replication of the DNA. It has revolutionized forensic science, medical diagnostics, and
biological research.
8. Which nitrogenous base is found in RNA but not in DNA?
A. Uracil
B. Thymine
C. Adenine
D. Guanine
Correct Answer: A
Explanation: In RNA, the pyrimidine base uracil replaces thymine, which is found in DNA.
Uracil pairs with adenine through two hydrogen bonds, similar to how thymine pairs with
adenine. This chemical difference helps cellular machinery distinguish between DNA for
storage and RNA for temporary messaging and catalysis.
9. What characterizes a recessive allele?
A. It is always the most common allele in a population.
B. It masks the expression of a dominant allele.
C. Its phenotype is expressed only when two copies are present.
D. It is always harmful to the organism.
Correct Answer: C
