BIOL 271 Microbiology w/ Lab | Module 6. Virus characterization,
morphology and pathogenic causative agents
200 Questions — Review Set
Question 1
What is a virus?
✓ Answer: A submicroscopic infectious agent that replicates only inside the living
cells of a host organism, consisting of genetic material (DNA or RNA) surrounded by a
protein coat.
Feedback: Viruses are obligate intracellular parasites that lack cellular machinery for metabolism and
reproduction, relying entirely on host cells for replication.
Question 2
What is the basic structure of a virus?
✓ Answer: A virus consists of a nucleic acid genome (DNA or RNA) enclosed within a
protein capsid, and some viruses have an additional lipid envelope derived from the
host cell membrane.
Feedback: The capsid protects the viral genome and facilitates attachment and entry into host cells, while
the envelope, when present, aids in infection and immune evasion.
Question 3
What is a capsid?
✓ Answer: The protein shell that surrounds and protects the viral nucleic acid
genome, composed of multiple protein subunits called capsomeres.
Feedback: Capsids can have various shapes, including icosahedral, helical, or complex structures, and are
critical for viral stability and infectivity.
Question 4
What are capsomeres?
✓ Answer: The individual protein subunits that assemble to form the viral capsid.
Feedback: Capsomeres self-assemble into the capsid structure, and their arrangement determines the overall
symmetry and shape of the virus particle.
Question 5
What is a viral envelope?
, ✓ Answer: A lipid bilayer membrane that surrounds the capsid of some viruses,
acquired from the host cell membrane during viral budding or release.
Feedback: The envelope contains viral glycoproteins that are essential for attachment and entry into host
cells, and it is sensitive to detergents, heat, and drying.
Question 6
What are viral spikes or peplomers?
✓ Answer: Glycoprotein projections on the surface of enveloped viruses that mediate
attachment to host cell receptors and facilitate entry.
Feedback: Spike proteins are often the primary targets for neutralizing antibodies and are key determinants
of viral host range and tissue tropism.
Question 7
What is the difference between enveloped and non-enveloped viruses?
✓ Answer: Enveloped viruses have a lipid membrane surrounding the capsid, while
non-enveloped viruses consist only of the capsid and nucleic acid genome.
Feedback: Enveloped viruses are generally more sensitive to environmental conditions and disinfectants,
while non-enveloped viruses are more resistant and often cause more persistent infections.
Question 8
What is an icosahedral capsid?
✓ Answer: A capsid with icosahedral symmetry, consisting of 20 equilateral triangular
faces and 12 vertices, providing a spherical appearance.
Feedback: Icosahedral symmetry is common among many animal viruses, including adenoviruses,
polioviruses, and herpesviruses, and allows for efficient packaging of the genome.
Question 9
What is a helical capsid?
✓ Answer: A capsid with helical symmetry, where capsomeres assemble in a helical or
spiral pattern around the nucleic acid, forming a rod-like or filamentous structure.
Feedback: Helical capsids are characteristic of viruses such as tobacco mosaic virus and influenza virus, and
the genome is often RNA.
Question 10
What is a complex capsid?
✓ Answer: A capsid structure that does not fit icosahedral or helical symmetry, such
as the complex structures found in poxviruses and bacteriophages.
,Feedback: Complex capsids may contain additional protein structures, such as tail fibers or outer layers, that
are specialized for specific functions like host cell recognition.
Question 11
What is a bacteriophage?
✓ Answer: A virus that infects and replicates within bacteria, characterized by
complex structures with a head, tail, and tail fibers.
Feedback: Bacteriophages are the most abundant biological entities on Earth and play important roles in
bacterial ecology, gene transfer, and biotechnology.
Question 12
What is the structure of a bacteriophage?
✓ Answer: A bacteriophage typically has an icosahedral head containing the nucleic
acid, a helical tail, and tail fibers for attachment to the bacterial cell surface.
Feedback: The tail structure is specialized for injecting the viral genome into the bacterial host through the
cell wall and membrane.
Question 13
What is the viral genome?
✓ Answer: The genetic material of a virus, which can be either DNA or RNA, single-
stranded or double-stranded, linear or circular.
Feedback: The viral genome contains the information necessary for replication, transcription, translation,
and assembly of new virus particles within the host cell.
Question 14
What types of viral genomes exist?
✓ Answer: Viruses can have double-stranded DNA (dsDNA), single-stranded DNA
(ssDNA), double-stranded RNA (dsRNA), or single-stranded RNA (ssRNA) genomes.
Feedback: The type of genome determines the viral replication strategy, the enzymes required for
replication, and the virus's classification in the Baltimore classification system.
Question 15
What is the Baltimore classification of viruses?
✓ Answer: A classification system that groups viruses based on their genome type
and replication strategy, with seven categories designated by Roman numerals I
through VII.
, Feedback: The Baltimore classification is fundamental for understanding viral replication mechanisms and
includes dsDNA, ssDNA, dsRNA, ssRNA (+), ssRNA (-), retroviruses, and DNA intermediate viruses.
Question 16
What is a positive-sense RNA virus?
✓ Answer: A virus with a single-stranded RNA genome that can serve directly as
messenger RNA (mRNA) and be translated into viral proteins by host ribosomes.
Feedback: Positive-sense RNA viruses, such as poliovirus and SARS-CoV-2, do not carry their own RNA
polymerase in the virion and rely on host or viral-encoded polymerases for replication.
Question 17
What is a negative-sense RNA virus?
✓ Answer: A virus with a single-stranded RNA genome that is complementary to
mRNA and must be transcribed into positive-sense RNA before translation can occur.
Feedback: Negative-sense RNA viruses, such as influenza virus and rabies virus, carry their own RNA-
dependent RNA polymerase within the virion to perform transcription.
Question 18
What is a retrovirus?
✓ Answer: A virus with a single-stranded RNA genome that replicates through a DNA
intermediate using the enzyme reverse transcriptase, converting RNA into DNA.
Feedback: Retroviruses, including HIV, integrate their viral DNA into the host genome, where it can persist
for the lifetime of the cell and cause chronic infections.
Question 19
What is reverse transcriptase?
✓ Answer: An enzyme unique to retroviruses that catalyzes the synthesis of DNA from
an RNA template, allowing the viral RNA genome to be converted into double-
stranded DNA.
Feedback: Reverse transcriptase lacks proofreading activity, leading to high mutation rates that contribute
to viral diversity and drug resistance in retroviruses like HIV.
Question 20
What is a provirus?
✓ Answer: A viral genome that has been integrated into the host cell's chromosomal
DNA, where it can be transcribed and replicated along with the host genome.
morphology and pathogenic causative agents
200 Questions — Review Set
Question 1
What is a virus?
✓ Answer: A submicroscopic infectious agent that replicates only inside the living
cells of a host organism, consisting of genetic material (DNA or RNA) surrounded by a
protein coat.
Feedback: Viruses are obligate intracellular parasites that lack cellular machinery for metabolism and
reproduction, relying entirely on host cells for replication.
Question 2
What is the basic structure of a virus?
✓ Answer: A virus consists of a nucleic acid genome (DNA or RNA) enclosed within a
protein capsid, and some viruses have an additional lipid envelope derived from the
host cell membrane.
Feedback: The capsid protects the viral genome and facilitates attachment and entry into host cells, while
the envelope, when present, aids in infection and immune evasion.
Question 3
What is a capsid?
✓ Answer: The protein shell that surrounds and protects the viral nucleic acid
genome, composed of multiple protein subunits called capsomeres.
Feedback: Capsids can have various shapes, including icosahedral, helical, or complex structures, and are
critical for viral stability and infectivity.
Question 4
What are capsomeres?
✓ Answer: The individual protein subunits that assemble to form the viral capsid.
Feedback: Capsomeres self-assemble into the capsid structure, and their arrangement determines the overall
symmetry and shape of the virus particle.
Question 5
What is a viral envelope?
, ✓ Answer: A lipid bilayer membrane that surrounds the capsid of some viruses,
acquired from the host cell membrane during viral budding or release.
Feedback: The envelope contains viral glycoproteins that are essential for attachment and entry into host
cells, and it is sensitive to detergents, heat, and drying.
Question 6
What are viral spikes or peplomers?
✓ Answer: Glycoprotein projections on the surface of enveloped viruses that mediate
attachment to host cell receptors and facilitate entry.
Feedback: Spike proteins are often the primary targets for neutralizing antibodies and are key determinants
of viral host range and tissue tropism.
Question 7
What is the difference between enveloped and non-enveloped viruses?
✓ Answer: Enveloped viruses have a lipid membrane surrounding the capsid, while
non-enveloped viruses consist only of the capsid and nucleic acid genome.
Feedback: Enveloped viruses are generally more sensitive to environmental conditions and disinfectants,
while non-enveloped viruses are more resistant and often cause more persistent infections.
Question 8
What is an icosahedral capsid?
✓ Answer: A capsid with icosahedral symmetry, consisting of 20 equilateral triangular
faces and 12 vertices, providing a spherical appearance.
Feedback: Icosahedral symmetry is common among many animal viruses, including adenoviruses,
polioviruses, and herpesviruses, and allows for efficient packaging of the genome.
Question 9
What is a helical capsid?
✓ Answer: A capsid with helical symmetry, where capsomeres assemble in a helical or
spiral pattern around the nucleic acid, forming a rod-like or filamentous structure.
Feedback: Helical capsids are characteristic of viruses such as tobacco mosaic virus and influenza virus, and
the genome is often RNA.
Question 10
What is a complex capsid?
✓ Answer: A capsid structure that does not fit icosahedral or helical symmetry, such
as the complex structures found in poxviruses and bacteriophages.
,Feedback: Complex capsids may contain additional protein structures, such as tail fibers or outer layers, that
are specialized for specific functions like host cell recognition.
Question 11
What is a bacteriophage?
✓ Answer: A virus that infects and replicates within bacteria, characterized by
complex structures with a head, tail, and tail fibers.
Feedback: Bacteriophages are the most abundant biological entities on Earth and play important roles in
bacterial ecology, gene transfer, and biotechnology.
Question 12
What is the structure of a bacteriophage?
✓ Answer: A bacteriophage typically has an icosahedral head containing the nucleic
acid, a helical tail, and tail fibers for attachment to the bacterial cell surface.
Feedback: The tail structure is specialized for injecting the viral genome into the bacterial host through the
cell wall and membrane.
Question 13
What is the viral genome?
✓ Answer: The genetic material of a virus, which can be either DNA or RNA, single-
stranded or double-stranded, linear or circular.
Feedback: The viral genome contains the information necessary for replication, transcription, translation,
and assembly of new virus particles within the host cell.
Question 14
What types of viral genomes exist?
✓ Answer: Viruses can have double-stranded DNA (dsDNA), single-stranded DNA
(ssDNA), double-stranded RNA (dsRNA), or single-stranded RNA (ssRNA) genomes.
Feedback: The type of genome determines the viral replication strategy, the enzymes required for
replication, and the virus's classification in the Baltimore classification system.
Question 15
What is the Baltimore classification of viruses?
✓ Answer: A classification system that groups viruses based on their genome type
and replication strategy, with seven categories designated by Roman numerals I
through VII.
, Feedback: The Baltimore classification is fundamental for understanding viral replication mechanisms and
includes dsDNA, ssDNA, dsRNA, ssRNA (+), ssRNA (-), retroviruses, and DNA intermediate viruses.
Question 16
What is a positive-sense RNA virus?
✓ Answer: A virus with a single-stranded RNA genome that can serve directly as
messenger RNA (mRNA) and be translated into viral proteins by host ribosomes.
Feedback: Positive-sense RNA viruses, such as poliovirus and SARS-CoV-2, do not carry their own RNA
polymerase in the virion and rely on host or viral-encoded polymerases for replication.
Question 17
What is a negative-sense RNA virus?
✓ Answer: A virus with a single-stranded RNA genome that is complementary to
mRNA and must be transcribed into positive-sense RNA before translation can occur.
Feedback: Negative-sense RNA viruses, such as influenza virus and rabies virus, carry their own RNA-
dependent RNA polymerase within the virion to perform transcription.
Question 18
What is a retrovirus?
✓ Answer: A virus with a single-stranded RNA genome that replicates through a DNA
intermediate using the enzyme reverse transcriptase, converting RNA into DNA.
Feedback: Retroviruses, including HIV, integrate their viral DNA into the host genome, where it can persist
for the lifetime of the cell and cause chronic infections.
Question 19
What is reverse transcriptase?
✓ Answer: An enzyme unique to retroviruses that catalyzes the synthesis of DNA from
an RNA template, allowing the viral RNA genome to be converted into double-
stranded DNA.
Feedback: Reverse transcriptase lacks proofreading activity, leading to high mutation rates that contribute
to viral diversity and drug resistance in retroviruses like HIV.
Question 20
What is a provirus?
✓ Answer: A viral genome that has been integrated into the host cell's chromosomal
DNA, where it can be transcribed and replicated along with the host genome.
