Virology (Brock - Chapter 5)

Viruses are considered obligate intracellular parasites because:
A) They can reproduce outside the host cell
B) They rely on the host cell for energy and protein synthesis
C) They can live independently in nature
D) They do not need host cells for reproduction

B

Which of the following is a characteristic of a virion?
A) It is the viral genome alone
B) It consists of the viral genome and a protein capsid
C) It contains ribosomes for protein synthesis
D) It can undergo cell division

B

Which of the following types of viruses has an outer lipid layer derived from the host cell membrane?
A) Naked viruses
B) Giant viruses
C) Enveloped viruses
D) Prophages

C

What is the protein shell surrounding the viral genome called?
A) Capsomere
B) Envelope
C) Nucleocapsid
D) Capsid

D

Which viral symmetry is typical of rod-shaped viruses?
A) Icosahedral symmetry
B) Radial symmetry
C) Complex symmetry
D) Helical symmetry

D

Which of the following viruses is an example of one that contains a helical symmetry?
A) Influenza virus
B) Tobacco mosaic virus (TMV)
C) Human papillomavirus
D) HIV

B

What is a feature of enveloped viruses that distinguishes them from naked viruses?
A) Enveloped viruses contain only RNA genomes
B) Enveloped viruses are surrounded by a lipid membrane from the host
C) Enveloped viruses have no capsid structure
D) Enveloped viruses do not infect animal cells

B

In a plaque assay, what does a clear zone in a bacterial lawn represent?
A) A growing bacterial colony
B) A dead bacterial colony
C) A zone where a virus has lysed bacterial cells
D) An area of healthy, growing bacteria

C

What is meant by the viral titer?
A) The concentration of viruses needed to infect 50% of a population
B) The number of viral particles per milliliter of suspension
C) The ability of a virus to cause disease
D) The number of viruses that fail to infect

B

Why is the number of plaque-forming units (PFUs) often lower than the actual number of viral particles in a sample?
A) Not all viruses infect the host cells successfully
B) Viral particles are too small to be detected
C) Some viruses don't form plaques
D) Host cells don't grow efficiently in lab conditions

A

The first step of the viral replication cycle is:
A) Synthesis of viral proteins
B) Assembly of new virions
C) Penetration of the host cell
D) Attachment to the host cell

D

Which phase of the viral replication cycle is characterized by the assembly of new virions?
A) Eclipse phase
B) Latent phase
C) Maturation phase
D) Lytic phase

C

What is the 'burst size' in viral replication?
A) The number of viruses required to infect a host
B) The number of virions released from a host cell after lysis
C) The amount of time it takes for a virus to infect a cell
D) The size of the viral genome

B

What determines the host specificity of bacteriophage T4?
A) The shape of the virus
B) The presence of specific receptors on the host cell
C) The size of the viral genome
D) The host cell's metabolic rate

B

Which part of the T4 bacteriophage enters the host cell during infection?
A) The entire virus
B) The viral genome only
C) The capsid
D) The tail fibers

B

What is the function of the lysozyme-like protein in bacteriophage T4?
A) To digest the host's cell wall and allow entry of the viral genome
B) To help the virus assemble its capsid
C) To inhibit host DNA replication
D) To trigger cell lysis after replication

A

What is a temperate virus?
A) A virus that only kills its host cell immediately
B) A virus that can establish a long-term stable relationship with its host
C) A virus that infects only eukaryotic cells
D) A virus that causes chronic infections in plants

B

When a temperate virus integrates its genome into the host's genome, what is it called?
A) A prophage
B) A plasmid
C) A virion
D) A capsid

A

What is the process called when a prophage becomes activated and enters the lytic cycle?
A) Transformation
B) Lysogeny
C) Induction
D) Transduction

C

A lysogenic cell contains:
A) Viral particles but no viral genome
B) A prophage integrated into its chromosome
C) Virions that are ready to be released
D) RNA from multiple viral genomes

B

Which of the following is NOT a key difference between bacterial and eukaryotic viruses?
A) Entire virions enter the host cells in eukaryotic viruses
B) Eukaryotic viruses can replicate in the nucleus
C) Eukaryotic viruses never contain DNA genomes
D) Eukaryotic viruses may form viral factories or viroplasms

C

What is the main method of entry for many eukaryotic viruses into host cells?
A) Osmosis
B) Endocytosis
C) Diffusion through the cell membrane
D) Viral budding

B

How do enveloped viruses typically exit an animal cell?
A) Via lysis of the host cell
B) Via budding from the host membrane
C) By forming endospores
D) Through host cell apoptosis

B

What is a latent infection in animal cells?
A) A type of infection where the host cell is immediately lysed
B) An infection where viral DNA integrates into the host genome and remains inactive
C) A rapid infection that results in cell death
D) A chronic infection that continuously produces new virions

B

In a persistent viral infection, what happens to the host cell?
A) The host cell is lysed immediately
B) The host cell remains alive and continues to produce virions
C) The host cell dies slowly over time
D) The virus is unable to replicate

B

Which of the following is true regarding viral genomes?
A) All viral genomes are made of DNA
B) Viral genomes can be composed of either DNA or RNA
C) All viruses have single-stranded genomes
D) Viral genomes are larger than most bacterial genomes

B

What is the term used for viruses that infect bacteria?
A) Phage
B) Prion
C) Retrovirus
D) Mycophage

A

Which of the following statements is true about giant viruses?
A) They only infect plants
B) They are larger than some bacterial cells
C) They contain fewer genes than smaller viruses
D) They cannot infect protozoa

B

How do viruses infecting plants typically gain access to plant cells?
A) Through direct fusion with the plant cell membrane
B) By entering through wounds or insect bites
C) By being carried in water
D) By diffusion across the cell wall

B

What is a vector in the context of plant viruses?
A) A type of plant that resists viral infection
B) An insect or organism that transmits viruses to plants
C) A chemical compound used to treat viral infections
D) A tool used to culture plant viruses

B

What enzyme is typically found in the virions of RNA viruses that is essential for their replication?
A) DNA polymerase
B) RNA replicase
C) Lysozyme
D) Reverse transcriptase

B

Which of the following is true about reverse transcriptase?
A) It is found only in DNA viruses
B) It is required to synthesize RNA from an RNA template
C) It converts RNA genomes into DNA
D) It is found in all bacteriophages

C

What role do neuraminidase enzymes play in influenza viruses?
A) They replicate the viral genome
B) They help release virions from infected cells by breaking down connective tissue
C) They aid in viral attachment to the host cell
D) They synthesize new viral proteins

B

What does the plaque assay measure?
A) The total number of viral particles in a sample
B) The number of infectious virions present per volume of fluid
C) The concentration of antibodies in response to infection
D) The size of a virus

B

Why is viral titer expressed as "plaque-forming units" (PFU) rather than an absolute viral number?
A) Not all virions can successfully infect host cells
B) Viruses are too small to count directly
C) Some viruses are resistant to plaque formation
D) The exact number of viruses cannot be known

A

What is the main characteristic of a temperate bacteriophage?
A) It immediately lyses the host cell upon infection.
B) It can enter a state of lysogeny, where the viral genome is integrated into the host.
C) It only infects eukaryotic cells.
D) It replicates independently of the host cell's DNA.

B

What triggers a temperate bacteriophage to switch from the lysogenic to the lytic cycle?
A) Excess nutrient availability
B) Environmental stress or damage to host DNA
C) The formation of viral capsids
D) Introduction of another bacteriophage

B

A bacterium harboring a prophage is called a:
A) Plasmid host
B) Lysogen
C) Virulent host
D) Naked bacterium

B

What is the result of lysogenic conversion?
A) The bacterial cell gains new genetic traits from the prophage.
B) The prophage kills the host immediately.
C) The virus produces multiple capsids inside the bacterial cell.
D) The virus converts the host into an animal cell.

A

Which enzyme is used by RNA viruses to replicate their RNA genome?
A) DNA polymerase
B) RNA replicase
C) Reverse transcriptase
D) Neuraminidase

B

Retroviruses, such as HIV, use which enzyme to convert their RNA genome into DNA?
A) RNA polymerase
B) Lysozyme
C) Reverse transcriptase
D) RNA replicase

C

Which viral enzyme is responsible for creating small holes in the bacterial cell wall to facilitate infection by bacteriophages?
A) Lysozyme
B) Reverse transcriptase
C) Neuraminidase
D) DNA polymerase

A

What distinguishes eukaryotic viruses from bacterial viruses in terms of replication?
A) Eukaryotic viruses can replicate in the cytoplasm only.
B) Only eukaryotic viruses can form viral factories (viroplasms).
C) Bacterial viruses replicate faster than eukaryotic viruses.
D) Only bacterial viruses carry their entire virion into the host cell.

B

What is the typical outcome of a latent infection in animal cells?
A) Immediate cell lysis and death
B) Viral DNA integrates into the host genome and remains inactive
C) Chronic infection without producing new virions
D) Continuous production of viral particles without host cell death

B

What is a common feature of giant viruses like Mimivirus that distinguishes them from smaller viruses?
A) They have fewer genes than smaller viruses.
B) Their genomes are larger than some bacterial genomes.
C) They only infect bacterial cells.
D) They cannot form capsids.

B

Which of the following is a viral vector in the context of plant viruses?
A) An insect or organism that transmits viruses to plants
B) A plant cell that resists viral infection
C) A viral protein that helps the virus move through the vascular system
D) A chemical used to block viral entry into the plant

A

True or False: The latent period in viral replication includes both the eclipse phase and the early maturation phase.
A) True
B) False, the latent period includes only the maturation phase.
C) False, it includes only the eclipse phase.
D) False, the latent period occurs after the release of virions.

A

True or False: RNA viruses carry an enzyme called reverse transcriptase to replicate their RNA genomes.
A) True
B) False, RNA viruses use RNA replicase.
C) False, reverse transcriptase is used by DNA viruses.
D) True, but only in bacteriophages.

B

True or False: Neuraminidase is an enzyme used by influenza viruses to help virions exit the host cell.
A) True
B) False, neuraminidase is used for viral genome replication.
C) False, neuraminidase helps the virus attach to the host cell.
D) False, neuraminidase breaks down host cell membranes to allow entry.

A

True or False: Enveloped viruses enter host cells by fusing their envelope with the host cell membrane.
A) True
B) False, enveloped viruses enter by endocytosis.
C) False, the envelope dissolves outside the cell before entry.
D) True, but only in bacterial cells.

A

True or False: In a latent viral infection, the virus integrates its genome into the host and remains inactive for a time.
A) True
B) False, latent viruses replicate immediately upon infection.
C) False, latent infections result in immediate cell lysis.
D) True, but the host cell must divide before the virus activates.

A

Which of the following is true about the viral capsid?
A) It is made of lipid bilayers.
B) It contains nucleic acids and enzymes.
C) It is composed of protein subunits called capsomeres.
D) It directly synthesizes viral proteins.

C

Which phase of the viral replication cycle is responsible for the synthesis of viral proteins and genomes?
A) Attachment
B) Eclipse phase
C) Maturation phase
D) Release phase

B

The structure of a naked virus is composed of:
A) A capsid and an envelope
B) A nucleic acid and a capsid
C) A nucleic acid, capsid, and glycoprotein spikes
D) A nucleocapsid and an envelope

B

During which stage of viral replication does the virus bind to the host cell surface?
A) Penetration
B) Attachment
C) Lysis
D) Assembly

B

Which of the following accurately describes the eclipse phase of viral replication?
A) The virions are actively being released from the host cell.
B) The viral genome is injected into the host cell, but no infectious particles can be detected.
C) The viral capsid assembles around the genome.
D) The host cell synthesizes its own proteins along with viral proteins.

D

In bacteriophage infection, what is the function of lysozyme?
A) It helps the virus attach to the host cell surface.
B) It creates a pore in the bacterial cell wall for viral genome entry.
C) It replicates the viral genome inside the host cell.
D) It synthesizes new viral capsids.

B

Which of the following can induce a temperate virus to switch from lysogeny to the lytic cycle?
A) Nutrient-rich conditions in the host environment
B) Environmental stress, such as UV radiation or DNA damage
C) Increased production of viral proteins
D) Mutation in the viral genome

B

How do enveloped viruses like HIV enter a host cell?
A) By being injected directly into the cytoplasm
B) By attaching to the host membrane and being engulfed via endocytosis
C) By fusing their viral envelope with the host's cell membrane
D) By entering through plasmodesmata

B

In animal cells, a persistent infection differs from a lytic infection in that:
A) Persistent infections result in the immediate destruction of the host cell.
B) Persistent infections lead to slow release of virions without killing the host.
C) Persistent infections occur only in plants.
D) Persistent infections involve the integration of the viral genome into the host DNA.

B

Which of the following statements about viral symmetry is true for complex viruses like bacteriophage T4?
A) They exhibit only helical symmetry, with the capsid arranged in a spiral structure.
B) They exhibit only icosahedral symmetry, forming a highly efficient closed shell.
C) They exhibit both icosahedral and helical symmetry, with the head showing icosahedral symmetry and the tail showing helical symmetry.
D) They have no symmetrical arrangement of their capsid proteins, making them irregular.

C

Enveloped viruses are known for their ability to fuse with host cell membranes. Which of the following correctly describes the role of the envelope in the viral life cycle?
A) The envelope is used solely for protecting the viral genome from environmental factors.
B) The envelope is derived from the host cell membrane and contains viral glycoproteins crucial for attachment and entry.
C) The envelope is synthesized entirely by viral enzymes within the host cell.
D) The envelope is not necessary for viral replication and is only present in retroviruses.

B

Which of the following best describes the burst size in the context of bacteriophage replication?
A) The number of bacteriophages that attach to a single bacterial cell during infection.
B) The number of new virions released from a host cell after lysis, which depends on both the virus type and host cell.
C) The time it takes for a viral genome to be replicated inside the host cell.
D) The number of capsids assembled inside the host before release.

B

In which situation would a virus need to undergo reverse transcription, and which enzyme is responsible for this process?
A) When an RNA virus enters a bacterial host, and RNA replicase facilitates the process.
B) When a retrovirus enters an animal cell, and reverse transcriptase converts RNA into DNA.
C) When a DNA virus infects a plant cell, and DNA polymerase transcribes RNA from DNA.
D) When an RNA virus infects a bacterial cell, and lysozyme facilitates reverse transcription.

B

During the early stages of viral infection, the host's machinery is hijacked to produce early viral proteins. Which of the following is typically associated with the function of early viral proteins in bacteriophage T4?
A) Formation of the viral capsid and assembly of new virions.
B) Production of enzymes that inhibit host DNA replication and initiate viral genome replication.
C) Degradation of viral RNA to prevent translation of viral proteins.
D) Assisting in the attachment of virions to other host cells.

B

Which of the following conditions must be met for a temperate bacteriophage to enter lysogeny instead of the lytic cycle?
A) The bacteriophage must fail to find a suitable host cell.
B) The host cell must be in poor nutritional conditions or under environmental stress, favoring the lysogenic state.
C) The host cell must be dividing rapidly, which prevents the bacteriophage from initiating the lytic cycle.
D) The bacteriophage must produce an enzyme that degrades host cell DNA before integrating its genome.

B

How does lysogenic conversion affect the host bacterium, and which of the following is a consequence of this process?
A) Lysogenic conversion results in immediate host cell lysis.
B) Lysogenic conversion alters the host bacterium's phenotype, potentially adding virulence factors or resistance to environmental stresses.
C) Lysogenic conversion permanently inhibits the bacteriophage's ability to return to the lytic cycle.
D) Lysogenic conversion leads to the elimination of the host genome, allowing the bacteriophage to replicate freely.

B

Which of the following best describes the relationship between giant viruses (such as Mimivirus) and their protozoan hosts, and how do these viruses differ from smaller viruses?
A) Giant viruses rely solely on their own metabolic pathways to replicate within protozoan hosts.
B) Giant viruses have larger genomes than some bacterial species, and they can encode proteins for complex processes usually seen in cellular organisms.
C) Giant viruses are only capable of infecting bacterial hosts and cannot infect eukaryotic organisms like protozoa.
D) Giant viruses do not rely on their host cell machinery for replication, unlike smaller viruses.

B

Some plant viruses utilize movement proteins during infection. What is the primary role of these movement proteins?
A) They degrade the plant cell wall to facilitate viral entry.
B) They enable viruses to move through plasmodesmata, allowing the virus to spread between plant cells.
C) They act as vectors for the virus, enabling transmission to other plants through insects.
D) They help the virus assemble its capsid within the host cell.

B

Why is it important to consider plating efficiency when quantifying viral titers in a plaque assay?
A) Plating efficiency measures the number of viral particles that are non-infectious.
B) Plating efficiency accounts for variations in how effectively viruses infect host cells, leading to a titer lower than the actual viral particle count.
C) Plating efficiency estimates how many viral particles will be lost during the incubation process.
D) Plating efficiency measures the viral growth rate and is used to determine the speed of infection.

B

Which of the following accurately describes the role of RNA-dependent RNA polymerase (RNA replicase) in RNA viruses?
A) It is responsible for synthesizing viral RNA from a DNA template inside the host cell.
B) It is needed to synthesize complementary RNA strands from the viral RNA template since host cells do not contain enzymes that can perform this function.
C) It is involved in integrating viral RNA into the host's genome during lysogeny.
D) It degrades host cell RNA to prevent translation of non-viral proteins.

B

In which scenario would the titer of a viral suspension be expressed as the number of "plaque-forming units" (PFU) per milliliter rather than an absolute viral number?
A) When the viral genome count is being measured.
B) When only the number of host cells lysed by the virus is relevant.
C) When variations in viral infectivity mean not all virions in a sample are capable of forming plaques.
D) When viruses form plaques but cannot replicate inside host cells.

C

Viral genomes are highly variable. Which of the following explains why some RNA viruses mutate more rapidly than DNA viruses?
A) RNA viruses encode DNA polymerase, which lacks proofreading ability.
B) RNA-dependent RNA polymerase lacks proofreading functions, leading to higher mutation rates.
C) RNA viruses replicate more slowly, increasing the chance for mutation.
D) RNA viruses contain larger genomes, which are more prone to errors during replication.

B

Why can temperate bacteriophages serve as agents of horizontal gene transfer between bacteria?
A) Lysogeny induces mutations in the bacterial genome that can be passed to other cells.
B) The prophage integrates into the host genome and can carry host genes with it during transduction.
C) They cause the host cell to produce plasmids, which can be transferred to neighboring bacteria.
D) They produce enzymes that degrade the host genome, forcing the transfer of viral genes.

B

RNA viruses like the influenza virus carry their own RNA-dependent RNA polymerase. What is the primary reason host cells cannot provide this enzyme?
A) Host cells are unable to synthesize proteins directly from RNA templates.
B) Host cells lack the ability to recognize viral RNA genomes as templates for protein synthesis.
C) Host cells contain only DNA-dependent RNA polymerase, which transcribes RNA from DNA templates.
D) Host cells contain reverse transcriptase instead, which is specific to DNA viruses.

C

Why might certain RNA viruses, such as those that infect plants, have such a broad host range, infecting hundreds of different species?
A) RNA viruses mutate rapidly due to the lack of proofreading by RNA replicase, allowing them to adapt to a wide variety of hosts.
B) RNA viruses contain large genomes that can encode multiple host-specific enzymes, increasing their infectivity.
C) RNA viruses are always enveloped, which allows them to bypass host immune systems.
D) RNA viruses replicate more slowly, giving them time to infect a variety of host cells.

A

In some cases, viral infections can be beneficial to the host organism. Which of the following is an example of a positive interaction between a virus and its host?
A) The human immunodeficiency virus (HIV) decreases the infectivity of other viruses during coinfection.
B) The hepatitis G virus (HGV) coinfection can decrease the replication rate of HIV in humans.
C) Viruses cause wing formation in insects, aiding in their dispersal but increasing their susceptibility to predators.
D) Influenza virus increases the host's resistance to other respiratory infections by activating the immune system.

B

Which of the following best explains why bacteriophages are frequently used as model systems for studying molecular biology and genetics?
A) Bacteriophages have simpler genomes than eukaryotic viruses, making them easier to manipulate.
B) Bacteriophages exhibit both lysogenic and lytic life cycles, allowing scientists to study gene expression and viral replication.
C) Bacteriophages do not infect eukaryotic cells, making them safer to work with in the lab.
D) Bacteriophages lack capsids, allowing for direct observation of their genetic material.

B

Which of the following is NOT a component of a typical virus?
A) Nucleic acid
B) Protein coat (capsid)
C) Cell membrane
D) Lipid envelope

C

What is the primary function of viral proteins?
A) To replicate the viral RNA
B) To form the viral envelope
C) To facilitate entry into host cells and hijack cellular machinery
D) To produce energy for the virus

C

How are viruses primarily classified?
A) By their size
B) By their method of transmission
C) By their genetic material (DNA or RNA)
D) By their color

C

Which of the following is an example of an RNA virus?
A) Herpes simplex virus
B) Influenza virus
C) Adenovirus
D) Epstein-Barr virus

B

How does the immune system recognize viral infections?
A) By detecting viral proteins on infected cells
B) By measuring body temperature
C) By the presence of antibodies only
D) By noticing cell shape changes

A

Antiviral drugs primarily work by:
A) Killing viruses directly
B) Stimulating the immune response
C) Inhibiting viral replication
D) Strengthening host cell membranes

C

What do serological tests detect in patients?
A) Viral DNA
B) Bacterial infections
C) Antibodies against specific viruses
D) Cell counts

C

One of the challenges in developing vaccines for rapidly mutating viruses is:
A) Their ability to remain dormant
B) Their rapid replication rate
C) The constant changes in their surface proteins
D) Their ability to infect animals

C

What type of viral infection leads to the host cell's death immediately after replication?
A) Latent infection
B) Lytic infection
C) Persistent infection
D) Transformation

B

How are many viral infections transmitted among animals?
A) Direct contact with infected bodily fluids
B) Contaminated water
C) Airborne particles
D) All of the above

D

What recent technology is being explored for the treatment of viral infections in animals?
A) CRISPR gene editing
B) Traditional antibiotics
C) Herbal remedies
D) Homeopathy

A

Which of the following is a common symptom of viral infection in plants?
A) Leaf wilting
B) Chlorosis (yellowing of leaves)
C) Stunted growth
D) All of the above

D

How are most plant viruses transmitted from one plant to another?
A) Through airborne spores
B) By soil contamination
C) By insect vectors, mechanical means, or contaminated tools
D) Only by water

C

Which of the following is a common insect vector for plant viruses?
A) Ants
B) Aphids
C) Ladybugs
D) Spiders

B

What laboratory technique is often used to detect plant viruses?
A) Polymerase Chain Reaction (PCR)
B) Gram staining
C) Gel electrophoresis
D) Enzyme-linked immunosorbent assay (ELISA)

D

Which of the following bacteriophage components is primarily responsible for binding to bacterial receptors?
A) Nucleic acid
B) Capsid proteins
C) Tail fibers
D) Lipid envelope

C

Which bacteriophage is known to infect E. coli by binding to the O-antigen of lipopolysaccharides?
A) T4 phage
B) Lambda phage
C) M13 phage
D) T7 phage

A

Which bacteriophage specifically binds to the maltose transport protein (lamB) in E. coli?
A) T7 phage
B) Lambda (λ) phage
C) M13 phage
D) ΦX174 phage

B

The M13 bacteriophage primarily attaches to which bacterial structure in E. coli?
A) Lipopolysaccharide (LPS)
B) F pilus
C) Cell wall
D) Ribosomes

B

What receptor is recognized by the T7 bacteriophage when infecting E. coli?
A) F pilus
B) Outer membrane protein (OMP) F
C) Teichoic acid
D) Pilin

B

Which receptor does the P1 bacteriophage utilize to infect E. coli?
A) Outer membrane protein (OMP) F
B) LPS
C) Teichoic acid
D) Peptidoglycan

B

Which receptor does the ΦX174 bacteriophage target on E. coli?
A) Ribosome
B) LPS
C) F pilus
D) Peptidoglycan

C