BIO111 Exam 3 Actual Exam V2 | BIO111 General Biology (BIO111
Exam 3) | UCLA
1. During which phase of the eukaryotic cell cycle is DNA synthesized?
A. G1 phase
B. G2 phase
C. S phase
D. M phase
Answer: C
Rationale: The S phase, or synthesis phase, is the specific period of the cell cycle when
DNA replication occurs. This process ensures that each chromosome is duplicated into two
sister chromatids before the cell enters mitosis. Proper regulation of this phase is critical to
maintain genomic stability in daughter cells.
2. What is the primary function of the enzyme helicase during DNA replication?
A. Unwinding the DNA double helix at the replication fork
B. Joining Okazaki fragments on the lagging strand
C. Adding nucleotides to the growing DNA strand
D. Synthesizing an RNA primer to start replication
Answer: A
Rationale: Helicase is an essential enzyme that breaks the hydrogen bonds between
complementary nitrogenous bases. By doing so, it unwinds the double-stranded DNA into
two single strands, creating a replication fork. This action provides the necessary template
for DNA polymerase to begin synthesis.
3. In a monohybrid cross between two heterozygous (Aa) individuals, what is the expected
phenotypic ratio of the offspring if A is completely dominant?
A. 3:1
B. 9:3:3:1
C. 1:2:1
D. 1:1
Answer: A
,Rationale: According to Mendelian genetics, a cross between two heterozygotes results in
three possible genotypes: AA, Aa, and aa. Because the ‘A’ allele is completely dominant,
both AA and Aa individuals will exhibit the dominant phenotype. This results in a 3:1 ratio
of dominant to recessive phenotypes among the progeny.
4. What unique event occurs during Prophase I of meiosis that increases genetic diversity?
A. Separation of sister chromatids
B. Replication of DNA
C. Crossing over between homologous chromosomes
D. Alignment of chromosomes at the metaphase plate
Answer: C
Rationale: Crossing over involves the physical exchange of genetic material between non-
sister chromatids of homologous chromosomes. This process occurs at sites called
chiasmata during synapsis in Prophase I. The resulting chromosomes are recombinant,
meaning they carry unique combinations of maternal and paternal alleles.
5. Which of the following best describes the ‘central dogma’ of molecular biology?
A. RNA -> DNA -> Protein
B. Protein -> RNA -> DNA
C. DNA -> Protein -> RNA
D. DNA -> RNA -> Protein
Answer: D
Rationale: The central dogma describes the flow of genetic information within a biological
system. It starts with transcription, where DNA is used as a template to create mRNA.
Subsequently, translation occurs, where the mRNA sequence is read by ribosomes to
synthesize a specific protein.
6. If a DNA sample contains 30% adenine, what is the expected percentage of cytosine?
A. 70%
B. 30%
C. 20%
D. 40%
Answer: C
Rationale: Chargaff’s rules state that the amount of adenine equals thymine and guanine
equals cytosine. Since adenine is 30%, thymine must also be 30%, totaling 60% for A-T
, pairs. The remaining 40% must be split equally between guanine and cytosine, resulting in
20% cytosine.
7. Which enzyme is responsible for synthesizing the RNA primer during DNA replication?
A. DNA Polymerase III
B. DNA Polymerase I
C. Primase
D. Ligase
Answer: C
Rationale: DNA polymerase requires a free 3’-OH group to begin adding nucleotides, which
it cannot create on its own. Primase, a type of RNA polymerase, synthesizes a short RNA
sequence complementary to the DNA template. This RNA primer provides the starting
point necessary for DNA synthesis to proceed.
8. A man with type AB blood and a woman with type O blood have children. What are the
possible blood types of their offspring?
A. Only AB and O
B. A, B, AB, and O
C. Only AB
D. Only A and B
Answer: D
Rationale: The man has the genotype IAIB, while the woman has the genotype ii. Each
child will receive one allele from each parent, resulting in either IAi (Type A) or IBi (Type
B). Because the O allele is recessive, the offspring can only express the A or B phenotypes.
9. What occurs during the process of translation?
A. DNA is copied into a new DNA molecule
B. mRNA is synthesized from a DNA template
C. Polypeptides are synthesized using the information in mRNA
D. Introns are removed from the pre-mRNA
Answer: C
Rationale: Translation is the process by which a ribosome decodes an mRNA message into
a polypeptide chain. Transfer RNA (tRNA) molecules bring specific amino acids to the
ribosome based on the mRNA codons. This process continues until a stop codon is reached,
signaling the completion of the protein.
Exam 3) | UCLA
1. During which phase of the eukaryotic cell cycle is DNA synthesized?
A. G1 phase
B. G2 phase
C. S phase
D. M phase
Answer: C
Rationale: The S phase, or synthesis phase, is the specific period of the cell cycle when
DNA replication occurs. This process ensures that each chromosome is duplicated into two
sister chromatids before the cell enters mitosis. Proper regulation of this phase is critical to
maintain genomic stability in daughter cells.
2. What is the primary function of the enzyme helicase during DNA replication?
A. Unwinding the DNA double helix at the replication fork
B. Joining Okazaki fragments on the lagging strand
C. Adding nucleotides to the growing DNA strand
D. Synthesizing an RNA primer to start replication
Answer: A
Rationale: Helicase is an essential enzyme that breaks the hydrogen bonds between
complementary nitrogenous bases. By doing so, it unwinds the double-stranded DNA into
two single strands, creating a replication fork. This action provides the necessary template
for DNA polymerase to begin synthesis.
3. In a monohybrid cross between two heterozygous (Aa) individuals, what is the expected
phenotypic ratio of the offspring if A is completely dominant?
A. 3:1
B. 9:3:3:1
C. 1:2:1
D. 1:1
Answer: A
,Rationale: According to Mendelian genetics, a cross between two heterozygotes results in
three possible genotypes: AA, Aa, and aa. Because the ‘A’ allele is completely dominant,
both AA and Aa individuals will exhibit the dominant phenotype. This results in a 3:1 ratio
of dominant to recessive phenotypes among the progeny.
4. What unique event occurs during Prophase I of meiosis that increases genetic diversity?
A. Separation of sister chromatids
B. Replication of DNA
C. Crossing over between homologous chromosomes
D. Alignment of chromosomes at the metaphase plate
Answer: C
Rationale: Crossing over involves the physical exchange of genetic material between non-
sister chromatids of homologous chromosomes. This process occurs at sites called
chiasmata during synapsis in Prophase I. The resulting chromosomes are recombinant,
meaning they carry unique combinations of maternal and paternal alleles.
5. Which of the following best describes the ‘central dogma’ of molecular biology?
A. RNA -> DNA -> Protein
B. Protein -> RNA -> DNA
C. DNA -> Protein -> RNA
D. DNA -> RNA -> Protein
Answer: D
Rationale: The central dogma describes the flow of genetic information within a biological
system. It starts with transcription, where DNA is used as a template to create mRNA.
Subsequently, translation occurs, where the mRNA sequence is read by ribosomes to
synthesize a specific protein.
6. If a DNA sample contains 30% adenine, what is the expected percentage of cytosine?
A. 70%
B. 30%
C. 20%
D. 40%
Answer: C
Rationale: Chargaff’s rules state that the amount of adenine equals thymine and guanine
equals cytosine. Since adenine is 30%, thymine must also be 30%, totaling 60% for A-T
, pairs. The remaining 40% must be split equally between guanine and cytosine, resulting in
20% cytosine.
7. Which enzyme is responsible for synthesizing the RNA primer during DNA replication?
A. DNA Polymerase III
B. DNA Polymerase I
C. Primase
D. Ligase
Answer: C
Rationale: DNA polymerase requires a free 3’-OH group to begin adding nucleotides, which
it cannot create on its own. Primase, a type of RNA polymerase, synthesizes a short RNA
sequence complementary to the DNA template. This RNA primer provides the starting
point necessary for DNA synthesis to proceed.
8. A man with type AB blood and a woman with type O blood have children. What are the
possible blood types of their offspring?
A. Only AB and O
B. A, B, AB, and O
C. Only AB
D. Only A and B
Answer: D
Rationale: The man has the genotype IAIB, while the woman has the genotype ii. Each
child will receive one allele from each parent, resulting in either IAi (Type A) or IBi (Type
B). Because the O allele is recessive, the offspring can only express the A or B phenotypes.
9. What occurs during the process of translation?
A. DNA is copied into a new DNA molecule
B. mRNA is synthesized from a DNA template
C. Polypeptides are synthesized using the information in mRNA
D. Introns are removed from the pre-mRNA
Answer: C
Rationale: Translation is the process by which a ribosome decodes an mRNA message into
a polypeptide chain. Transfer RNA (tRNA) molecules bring specific amino acids to the
ribosome based on the mRNA codons. This process continues until a stop codon is reached,
signaling the completion of the protein.
