BIOL 271 | BIOL271 Module 7: Microbiology
Updated and Latest Questions and Correct
Answers with Rationale - Portage Learning
1. Which of the following structural components is found in every viral particle regardless of
its complexity?
A. A phospholipid bilayer envelope
B. Ribosomes for independent protein synthesis
C. A nucleocapsid composed of nucleic acid and protein
D. Mitochondria for energy production
Correct Answer: C
Explanation: All viruses consist of at least a nucleic acid genome surrounded by a protein
coat called a capsid. The combination of these two elements is referred to as the
nucleocapsid. While some viruses have an additional lipid envelope, it is not a universal
characteristic of all viruses. Viruses lack cellular organelles like ribosomes and
mitochondria because they are acellular entities. This fundamental structure is necessary
for the virus to protect its genome and facilitate entry into a host cell.
2. What is the primary reason why viruses are classified as obligate intracellular parasites?
A. They possess a cell wall that requires host nutrients
B. They can only replicate within a living host cell
C. They are larger than most bacterial cells
D. They use binary fission to reproduce
Correct Answer: B
Explanation: Viruses lack the metabolic machinery and ribosomes necessary to generate
energy or synthesize proteins independently. Therefore, they must invade a susceptible
host cell and hijack its machinery to produce new viral components. Outside of a host cell, a
virus exists as an inert particle called a virion. Unlike bacteria, viruses do not reproduce via
binary fission but through a complex assembly process. This total dependence on the host
cell defines their status as obligate intracellular parasites.
3. Which viral enzyme is specifically required by retroviruses to convert their RNA genome
into DNA?
A. DNA-dependent RNA polymerase
B. RNA-dependent RNA polymerase
C. Lysozyme
,D. Reverse transcriptase
Correct Answer: D
Explanation: Retroviruses, such as HIV, carry a unique enzyme called reverse
transcriptase within their virion. This enzyme allows the virus to synthesize a
complementary DNA strand from its single-stranded RNA template. This process is the
reverse of the normal central dogma of molecular biology. Once the DNA is formed, it can
be integrated into the host cell’s genome as a provirus. Without this enzyme, the retrovirus
would be unable to establish a permanent infection within the host.
4. During the lytic cycle of a bacteriophage, which step involves the release of enzymes to
weaken the bacterial cell wall?
A. Attachment
B. Release
C. Biosynthesis
D. Penetration
Correct Answer: B
Explanation: In the final stage of the lytic cycle, the bacteriophage must escape the host
bacterium to infect new cells. To do this, the virus produces enzymes like lysozyme that
degrade the peptidoglycan in the bacterial cell wall. The weakened wall eventually
ruptures due to osmotic pressure, leading to cell lysis. This process results in the
immediate death of the host cell and the liberation of many new virions. This mechanism is
distinct from budding, which is more common in animal viruses.
5. In the lysogenic cycle, the integrated viral DNA within the bacterial chromosome is called a:
A. Viroid
B. Prion
C. Prophage
D. Capsid
Correct Answer: C
Explanation: The lysogenic cycle involves the integration of the bacteriophage genome
into the host’s DNA rather than immediate replication. This integrated viral genetic
material is specifically known as a prophage. The prophage is replicated along with the
bacterial DNA every time the cell divides. This allows the virus to persist in a latent state
without killing the host immediately. Environmental stressors can later trigger the
prophage to excise itself and enter the lytic cycle.
, 6. Which of the following characterizes the ‘uncoating’ step in the replication of an animal
virus?
A. The virus attaches to specific receptors on the cell membrane
B. The viral nucleic acid is released from the capsid
C. New viral proteins are synthesized by host ribosomes
D. The viral envelope fuses with the host plasma membrane
Correct Answer: B
Explanation: Uncoating is a critical stage that occurs after the virus has entered the host
cell via endocytosis or fusion. During this process, the protective protein capsid is removed
by host or viral enzymes. This release allows the viral nucleic acid to become available for
transcription and replication within the cytoplasm or nucleus. If uncoating does not occur,
the viral genome remains trapped and cannot initiate infection. This step is a common
target for certain types of antiviral drug therapies.
7. Which type of viral genome can be immediately translated into proteins by the host’s
ribosomes upon entry?
A. dsDNA
B. Negative-sense ssRNA
C. Positive-sense ssRNA
D. ssDNA
Correct Answer: C
Explanation: Positive-sense single-stranded RNA (+ssRNA) genomes act directly as
messenger RNA (mRNA). Because they mimic host mRNA, the host’s ribosomes can
recognize and translate them into viral proteins immediately. In contrast, negative-sense
RNA must first be transcribed into a positive strand by a viral RNA polymerase. DNA
viruses must typically undergo transcription in the nucleus before translation can occur.
This direct translation allows +ssRNA viruses to initiate the replication cycle very rapidly.
8. What is the primary function of viral ‘spikes’ (glycoproteins) located on the surface of some
viruses?
A. To aid in the attachment to specific host cell receptors
B. To provide motility to the virus
C. To synthesize ATP for the virus
D. To protect the nucleic acid from UV radiation
Correct Answer: A
Updated and Latest Questions and Correct
Answers with Rationale - Portage Learning
1. Which of the following structural components is found in every viral particle regardless of
its complexity?
A. A phospholipid bilayer envelope
B. Ribosomes for independent protein synthesis
C. A nucleocapsid composed of nucleic acid and protein
D. Mitochondria for energy production
Correct Answer: C
Explanation: All viruses consist of at least a nucleic acid genome surrounded by a protein
coat called a capsid. The combination of these two elements is referred to as the
nucleocapsid. While some viruses have an additional lipid envelope, it is not a universal
characteristic of all viruses. Viruses lack cellular organelles like ribosomes and
mitochondria because they are acellular entities. This fundamental structure is necessary
for the virus to protect its genome and facilitate entry into a host cell.
2. What is the primary reason why viruses are classified as obligate intracellular parasites?
A. They possess a cell wall that requires host nutrients
B. They can only replicate within a living host cell
C. They are larger than most bacterial cells
D. They use binary fission to reproduce
Correct Answer: B
Explanation: Viruses lack the metabolic machinery and ribosomes necessary to generate
energy or synthesize proteins independently. Therefore, they must invade a susceptible
host cell and hijack its machinery to produce new viral components. Outside of a host cell, a
virus exists as an inert particle called a virion. Unlike bacteria, viruses do not reproduce via
binary fission but through a complex assembly process. This total dependence on the host
cell defines their status as obligate intracellular parasites.
3. Which viral enzyme is specifically required by retroviruses to convert their RNA genome
into DNA?
A. DNA-dependent RNA polymerase
B. RNA-dependent RNA polymerase
C. Lysozyme
,D. Reverse transcriptase
Correct Answer: D
Explanation: Retroviruses, such as HIV, carry a unique enzyme called reverse
transcriptase within their virion. This enzyme allows the virus to synthesize a
complementary DNA strand from its single-stranded RNA template. This process is the
reverse of the normal central dogma of molecular biology. Once the DNA is formed, it can
be integrated into the host cell’s genome as a provirus. Without this enzyme, the retrovirus
would be unable to establish a permanent infection within the host.
4. During the lytic cycle of a bacteriophage, which step involves the release of enzymes to
weaken the bacterial cell wall?
A. Attachment
B. Release
C. Biosynthesis
D. Penetration
Correct Answer: B
Explanation: In the final stage of the lytic cycle, the bacteriophage must escape the host
bacterium to infect new cells. To do this, the virus produces enzymes like lysozyme that
degrade the peptidoglycan in the bacterial cell wall. The weakened wall eventually
ruptures due to osmotic pressure, leading to cell lysis. This process results in the
immediate death of the host cell and the liberation of many new virions. This mechanism is
distinct from budding, which is more common in animal viruses.
5. In the lysogenic cycle, the integrated viral DNA within the bacterial chromosome is called a:
A. Viroid
B. Prion
C. Prophage
D. Capsid
Correct Answer: C
Explanation: The lysogenic cycle involves the integration of the bacteriophage genome
into the host’s DNA rather than immediate replication. This integrated viral genetic
material is specifically known as a prophage. The prophage is replicated along with the
bacterial DNA every time the cell divides. This allows the virus to persist in a latent state
without killing the host immediately. Environmental stressors can later trigger the
prophage to excise itself and enter the lytic cycle.
, 6. Which of the following characterizes the ‘uncoating’ step in the replication of an animal
virus?
A. The virus attaches to specific receptors on the cell membrane
B. The viral nucleic acid is released from the capsid
C. New viral proteins are synthesized by host ribosomes
D. The viral envelope fuses with the host plasma membrane
Correct Answer: B
Explanation: Uncoating is a critical stage that occurs after the virus has entered the host
cell via endocytosis or fusion. During this process, the protective protein capsid is removed
by host or viral enzymes. This release allows the viral nucleic acid to become available for
transcription and replication within the cytoplasm or nucleus. If uncoating does not occur,
the viral genome remains trapped and cannot initiate infection. This step is a common
target for certain types of antiviral drug therapies.
7. Which type of viral genome can be immediately translated into proteins by the host’s
ribosomes upon entry?
A. dsDNA
B. Negative-sense ssRNA
C. Positive-sense ssRNA
D. ssDNA
Correct Answer: C
Explanation: Positive-sense single-stranded RNA (+ssRNA) genomes act directly as
messenger RNA (mRNA). Because they mimic host mRNA, the host’s ribosomes can
recognize and translate them into viral proteins immediately. In contrast, negative-sense
RNA must first be transcribed into a positive strand by a viral RNA polymerase. DNA
viruses must typically undergo transcription in the nucleus before translation can occur.
This direct translation allows +ssRNA viruses to initiate the replication cycle very rapidly.
8. What is the primary function of viral ‘spikes’ (glycoproteins) located on the surface of some
viruses?
A. To aid in the attachment to specific host cell receptors
B. To provide motility to the virus
C. To synthesize ATP for the virus
D. To protect the nucleic acid from UV radiation
Correct Answer: A
