BIOD 171 | BIOD 171 Microbiology Module 4 Exam
| Questions with Correct Answers and Expert
Explanation for Each Question | Portage Learning
1. Which enzyme is responsible for unwinding the DNA double helix during the
initiation of replication?
A. DNA Polymerase III
B. DNA Ligase
C. DNA Helicase
D. RNA Primase
Correct Answer: C
Expert Explanation: DNA helicase plays a critical role in replication by breaking
the hydrogen bonds between nitrogenous bases. This action unwinds the double
helix to create a replication fork for other enzymes to access. Without helicase
activity, the DNA strands would remain coiled and inaccessible for synthesis. The
energy for this process is derived from ATP hydrolysis as the enzyme moves along
the strand. It is the first essential step in preparing the genome for duplication in
microorganisms.
2. In microbial genetics, what is the specific role of DNA Polymerase III?
A. To add nucleotides to the 3’ end of the growing DNA strand
,B. To synthesize a short RNA primer to start replication
C. To seal gaps between Okazaki fragments on the lagging strand
D. To proofread the DNA and remove RNA primers
Correct Answer: A
Expert Explanation: DNA Polymerase III is the primary enzyme responsible for
synthesizing new DNA strands in prokaryotes. It functions by adding
deoxynucleotides to the 3’ hydroxyl group of an existing nucleotide chain. This
enzyme requires a primer to begin synthesis because it cannot start a strand from
scratch. Its high processivity allows for rapid and accurate replication of the
bacterial chromosome. This mechanism ensures that the genetic information is
faithfully passed to the next generation.
3. Which of the following describes the synthesis of the lagging strand during DNA
replication?
A. Continuous synthesis in the 5’ to 3’ direction
B. Synthesis moving directly toward the replication fork
C. Synthesis that does not require an RNA primer
D. Discontinuous synthesis using Okazaki fragments
Correct Answer: D
,Expert Explanation: The lagging strand is synthesized discontinuously because
DNA polymerase can only add nucleotides in a 5’ to 3’ direction. As the replication
fork opens, the enzyme must restart synthesis in short segments known as Okazaki
fragments. Each fragment requires its own RNA primer to provide a starting point
for the polymerase. Once synthesized, these fragments are eventually joined
together by DNA ligase to form a complete strand. This semi-discontinuous model is
a hallmark of DNA replication in all living organisms.
4. What is the function of the promoter region in a microbial gene?
A. It marks the site where translation begins on the ribosome
B. It signals the end of the transcription process
C. It serves as the binding site for the tRNA anticodon
D. It is the sequence where RNA polymerase binds to start transcription
Correct Answer: D
Expert Explanation: The promoter is a specific DNA sequence located upstream of
a gene that acts as a recruitment site. RNA polymerase recognizes this sequence to
correctly position itself for the start of transcription. In bacteria, specific sigma
factors help the polymerase identify different types of promoters. The efficiency of
binding at the promoter determines how frequently a particular gene is transcribed
, into mRNA. Therefore, the promoter serves as a primary regulatory point for gene
expression in microbes.
5. During transcription, which nitrogenous base in RNA pairs with adenine on the DNA
template?
A. Uracil
B. Cytosine
C. Guanine
D. Thymine
Correct Answer: A
Expert Explanation: In RNA synthesis, uracil replaces thymine as the
complementary base to adenine. This difference is one of the key chemical
distinctions between DNA and RNA molecules. When RNA polymerase reads an
adenine on the template DNA, it inserts a uracil into the growing RNA chain. This
base pairing follows the standard rules of molecular complementarity necessary for
accurate information transfer. Understanding this substitution is vital for tracing
genetic sequences from DNA to functional RNA.
6. What occurs during the process of translation in a bacterial cell?
A. DNA is copied into a complementary mRNA strand
B. The cell takes up naked DNA from the environment
| Questions with Correct Answers and Expert
Explanation for Each Question | Portage Learning
1. Which enzyme is responsible for unwinding the DNA double helix during the
initiation of replication?
A. DNA Polymerase III
B. DNA Ligase
C. DNA Helicase
D. RNA Primase
Correct Answer: C
Expert Explanation: DNA helicase plays a critical role in replication by breaking
the hydrogen bonds between nitrogenous bases. This action unwinds the double
helix to create a replication fork for other enzymes to access. Without helicase
activity, the DNA strands would remain coiled and inaccessible for synthesis. The
energy for this process is derived from ATP hydrolysis as the enzyme moves along
the strand. It is the first essential step in preparing the genome for duplication in
microorganisms.
2. In microbial genetics, what is the specific role of DNA Polymerase III?
A. To add nucleotides to the 3’ end of the growing DNA strand
,B. To synthesize a short RNA primer to start replication
C. To seal gaps between Okazaki fragments on the lagging strand
D. To proofread the DNA and remove RNA primers
Correct Answer: A
Expert Explanation: DNA Polymerase III is the primary enzyme responsible for
synthesizing new DNA strands in prokaryotes. It functions by adding
deoxynucleotides to the 3’ hydroxyl group of an existing nucleotide chain. This
enzyme requires a primer to begin synthesis because it cannot start a strand from
scratch. Its high processivity allows for rapid and accurate replication of the
bacterial chromosome. This mechanism ensures that the genetic information is
faithfully passed to the next generation.
3. Which of the following describes the synthesis of the lagging strand during DNA
replication?
A. Continuous synthesis in the 5’ to 3’ direction
B. Synthesis moving directly toward the replication fork
C. Synthesis that does not require an RNA primer
D. Discontinuous synthesis using Okazaki fragments
Correct Answer: D
,Expert Explanation: The lagging strand is synthesized discontinuously because
DNA polymerase can only add nucleotides in a 5’ to 3’ direction. As the replication
fork opens, the enzyme must restart synthesis in short segments known as Okazaki
fragments. Each fragment requires its own RNA primer to provide a starting point
for the polymerase. Once synthesized, these fragments are eventually joined
together by DNA ligase to form a complete strand. This semi-discontinuous model is
a hallmark of DNA replication in all living organisms.
4. What is the function of the promoter region in a microbial gene?
A. It marks the site where translation begins on the ribosome
B. It signals the end of the transcription process
C. It serves as the binding site for the tRNA anticodon
D. It is the sequence where RNA polymerase binds to start transcription
Correct Answer: D
Expert Explanation: The promoter is a specific DNA sequence located upstream of
a gene that acts as a recruitment site. RNA polymerase recognizes this sequence to
correctly position itself for the start of transcription. In bacteria, specific sigma
factors help the polymerase identify different types of promoters. The efficiency of
binding at the promoter determines how frequently a particular gene is transcribed
, into mRNA. Therefore, the promoter serves as a primary regulatory point for gene
expression in microbes.
5. During transcription, which nitrogenous base in RNA pairs with adenine on the DNA
template?
A. Uracil
B. Cytosine
C. Guanine
D. Thymine
Correct Answer: A
Expert Explanation: In RNA synthesis, uracil replaces thymine as the
complementary base to adenine. This difference is one of the key chemical
distinctions between DNA and RNA molecules. When RNA polymerase reads an
adenine on the template DNA, it inserts a uracil into the growing RNA chain. This
base pairing follows the standard rules of molecular complementarity necessary for
accurate information transfer. Understanding this substitution is vital for tracing
genetic sequences from DNA to functional RNA.
6. What occurs during the process of translation in a bacterial cell?
A. DNA is copied into a complementary mRNA strand
B. The cell takes up naked DNA from the environment
