Question 1

Which of the following statements best supports the argument that viruses are nonliving?
A) They do not carry out metabolic processes.
B) Their DNA does not encode proteins.
C) They have RNA rather than DNA.
D) They do not evolve.

Accepted Answer

Viruses do not carry out metabolic processes on their own; instead, they rely on the host cell's machinery for replication, energy production, and other life-sustaining activities, distinguishing them from living organisms that perform their own metabolism.

Question 2

The host range of a virus is determined by whether ________.
A) the enzymes carried by the virus are compatible with the host
B) the genome of the virus is made of DNA or RNA
C) it is an enveloped or non-enveloped virus
D) the proteins on virus surface can bind with proteins on the host surface

Accepted Answer

The host range of a virus is primarily determined by the ability of the virus's surface proteins to bind with specific receptor proteins on the surface of the host cell. This interaction is crucial for the virus to attach to and enter the host cell, initiating infection.

Question 3

Use the following figure and information to answer the question.  Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. All intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined.
Based on the data provided, the lytic cycle of virus B is closest to ________.
A) 15 minutes
B) 30 minutes
C) 45 minutes
D) 60 minutes

Accepted Answer

D

Question 4

A newly identified virus has a single-stranded RNA genome that is used as mRNA after infection. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. Which of the following processes would be the best to follow to analyze the reproduction of this virus in a host cell?
A) DNA replication rate
B) mRNA splicing
C) translation rate
D) formation of new transcription factors

Accepted Answer

Since the virus has a single-stranded RNA genome that is used directly as mRNA, the most relevant process to analyze for understanding its reproduction in a host cell would be the translation rate. This is because the viral RNA needs to be translated into proteins for the virus to replicate and produce new virions.

Question 5

Which of the following events or characteristics is the most likely explanation for why an individual experiences regular herpesvirus-mediated cold sore or genital sore flare-ups?
A) They have been reinfection by exposure to a different, but closely related herpesvirus strain.
B) They have been reinfection by exposure to the same herpesvirus strain.
C) Copies of the herpesvirus genome permanently maintained in host nuclei are periodically "activated."
D) Copies of herpesvirus particles that have escaped the immune system periodically experience conditions that allow them to replicate and infect cells.

Accepted Answer

Herpesviruses establish latency, meaning the virus's genome is maintained in a dormant state within the host's cells, often for the lifetime of the host. Periodic reactivation of these latent viruses can lead to recurrent outbreaks of symptoms, such as cold sores or genital sores, without the need for reinfection.

Question 6

Which of the following descriptions correctly identifies a main structural difference between viruses with envelopes and viruses without envelopes?
A) Only viruses with envelopes have their contents enclosed by a layer containing lipids
B) Only viruses with envelopes package their genetic material by engulfing it.
C) Only viruses without envelopes can release their genetic material into the cytoplasm of the host.
D) Only viruses without envelopes interact with receptor proteins on the surface of the host cell.

Accepted Answer

Viruses with envelopes have an outer lipid layer that surrounds the capsid, which is not found in non-enveloped viruses. This lipid layer is derived from the host cell membrane as the virus buds out, incorporating lipids and membrane proteins from the host.

Question 7

Since viral gene expression is regulated by the same machinery as host cell gene expression, which of the following is most likely involved in regulating expression of bacteriophage genes?
A) regulation via acetylation of histones
B) positive control mechanisms rather than negative
C) coordinate control of more than one gene in an operon
D) reliance on transcription activators

Accepted Answer

Bacteriophages, being viruses that infect bacteria, utilize the bacterial machinery for gene expression. Bacteria often regulate genes through operons, which allow for the coordinate control of multiple genes involved in a common pathway. This system is different from eukaryotic systems, which might use mechanisms like histone acetylation or transcription activators more extensively.

Question 8

Use the figures to answer the question.  Which of the three types of viruses shown would you expect to have glycoproteins among its components?
A) I only
B) III only
C) I and II only
D) II and III only

Accepted Answer

The answer of Use the figures to answer the question....

Question 9

Which of the following correctly describes the viral assembly process?
A) Host cell chaperone proteins mediate assembly of viral components.
B) Assembly proteins coded for by the host genome mediate assembly of viral components.
C) Assembly proteins coded for by the viral genome mediate assembly of viral components.
D) New viral components self-assemble without help from cellular components.

Accepted Answer

The answer of Which of the following correctly describes the...

Question 10

Use the figures to answer the question.  Which of the three types of viruses shown in the figure would you expect to include a capsid(s)?
A) I only
B) III only
C) I and II only
D) I, II, and III

Accepted Answer

The answer of Use the figures to answer the question....

Question 11

Use the following information to answer the question.
Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. The RNA genome has a 5′ RNA cap instead of a 5′ methyl-G cap. This is followed by a non-translated leader sequence and then a single long protein-coding region (~7,000 nucleotides) followed by a poly-A tail. Infected cells were incubated with radioactive amino acids and viral proteins were isolated. After a short incubation with radioactive amino acids only very long viral proteins were seen, while longer periods of labeling result in several short polypeptides of different lengths.
Which of the following conclusions is most consistent with the results described?
A) Host cell ribosomes translate the viral coding region and poly-A tail at different times resulting in the different populations of proteins.
B) The RNA is first translated into a single long protein, which is then cleaved into shorter ones.
C) The RNA is translated into short polypeptides, which are then assembled into large complexes.
D) The large radioactive polypeptides are coded by the host, whereas the short ones are coded for by the virus.

Accepted Answer

The observation that only very long viral proteins are seen after a short incubation with radioactive amino acids, with several short polypeptides appearing after longer periods, suggests that the RNA is first translated into a single long protein. This protein is then cleaved into shorter ones, consistent with the processing of poliovirus proteins.

Question 12

Use the following figure and information to answer the question.  Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. All intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined and plotted in the graph above.
In a second experiment, 1 mL of each viral sample collected at 90 minutes post infection was mixed with new, uninfected cell cultures. Which of the following best describes these new cultures?
A) The new culture infected with virus A will require 60 minutes before new viral particles will be released into the culture.
B) The new culture infected with virus A will result in more infected cells than the new culture infected with virus B.
C) The new culture infected with virus B will have a shorter lytic cycle than seen in the original virus B culture.
D) The new culture infected with virus B will plateau with approximately 50,000 viral particles per milliliter of culture.

Accepted Answer

The answer of Use the following figure and information to...

Question 13

The virus genome and viral proteins are assembled into virus particles during which of the following parts of the reproductive cycle?
A) the lytic cycle and the lysogenic cycle in all known host organisms
B) the lysogenic cycle only
C) the lytic cycle only
D) the lytic cycle in all host organisms but the lysogenic cycle only in bacteria

Accepted Answer

The assembly of virus particles occurs during the lytic cycle, where the virus takes over the host cell machinery to produce new viral particles, leading to cell lysis and release of the viruses. The lysogenic cycle involves integration of viral DNA into the host genome without immediate production of new viruses.

Question 14

Electron micrographs of herpes simplex virus (HSV) infection show the following progression; the intact virus first interacts with cell-surface proteoglycans and then with specific receptors, viral capsids dock with nuclear pores, and, finally, capsids go from being full to being "empty." Which of the following statements best fits these observations?
A) Viral capsids are needed for the cell to become infected; its proteins mediate binding with specific cells.
B) The viral envelope is not required for infectivity; its components do not enter the nucleus.
C) Only the genetic material of the virus is involved in infection; it is injected into the cytoplasm like the genome of a phage.
D) The viral envelope mediates entry into the cell; the viral genome is all that enters the nucleus.

Accepted Answer

The progression described indicates that the viral envelope facilitates the virus's entry into the cell, and only the viral genome (indicated by the capsids going from full to empty) enters the nucleus, which aligns with choice D.

Question 15

Viruses can carry out which of the following processes?
A) They can manufacture their own ATP, proteins, and nucleic acids.
B) They can use the host cell machinery to make copies of viral genomes and viral proteins.
C) They can use the host cell as a source of energy allowing viral machinery to replicate the virus.
D) They can replicate while within a host cell as well as when they are between host cells.

Accepted Answer

Viruses lack the cellular machinery necessary for self-replication and must use the host cell's machinery to replicate their genomes and produce viral proteins.

Question 16

Use the following figure and information to answer the question below.  Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. All intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined.
Based on the data provided, the lytic cycle of virus A is closest to ________.
A) 15 minutes
B) 30 minutes
C) 45 minutes
D) 90 minutes

Accepted Answer

The answer of Use the following figure and information to...

Question 17

Which of the following characteristics is typical of the lytic cycle of a bacteriophage?
A) Viral DNA incorporates into the host genome.
B) The viral genome replicates without destroying the host.
C) The host membrane ruptures, releasing many phages.
D) The host sequesters viral particles in the lysosome.

Accepted Answer

The lytic cycle of a bacteriophage typically ends with the rupture of the host cell membrane, leading to the release of newly formed phage particles. This process destroys the host cell.

Question 18

Which of the following statements accurately describes the lysogenic cycle of lambda (λ) phage?
A) The viral genes immediately turn the host cell into a lambda-producing factory. Then the host lyses.
B) The product of one prophage gene is made and it activates most of the other prophage genes.
C) The phage genome is integrated in the host chromosome where it is passed on to daughter cells through binary fission.
D) The phage DNA is copied and accumulates in the cytoplasm. Then a trigger causes capsid proteins to be made and phages are assembled.

Accepted Answer

The lysogenic cycle involves the integration of the phage genome into the host chromosome, where it can be replicated along with the host DNA and passed on to daughter cells during binary fission. This allows the phage to persist in the host without causing immediate lysis.

Question 19

What is the function of reverse transcriptase in retroviruses?
A) It uses viral RNA as a template for DNA synthesis.
B) It converts host cell RNA into viral DNA.
C) It translates viral RNA into proteins.
D) It uses viral RNA as a template for making more viral RNA strands.

Accepted Answer

Reverse transcriptase in retroviruses uses viral RNA as a template to synthesize complementary DNA (cDNA), which is then integrated into the host cell's genome. This process is essential for the replication cycle of retroviruses.

Question 20

Which of the following characteristics correctly describes retroviruses?
A) They are not destroyed or deactivated by heating.
B) They can only reproduce by infecting bacteria.
C) They have a single-stranded DNA that is integrated into the host cell genome.
D) They have a single-stranded RNA that acts as a template for DNA synthesis.

Accepted Answer

Retroviruses have a single-stranded RNA genome that, upon infection of a host cell, is reverse-transcribed into DNA, which then integrates into the host cell's genome. This process is facilitated by the enzyme reverse transcriptase, which retroviruses carry, allowing them to use RNA as a template for DNA synthesis.

Quiz 26: Introduction to Viruses

Which of the following statements best supports the argument that viruses are nonliving?

The host range of a virus is determined by whether ________.

A newly identified virus has a single-stranded RNA genome that is used as mRNA after infection. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. Which of the following processes would be the best to follow to analyze the reproduction of this virus in a host cell?

Which of the following events or characteristics is the most likely explanation for why an individual experiences regular herpesvirus-mediated cold sore or genital sore flare-ups?

Which of the following descriptions correctly identifies a main structural difference between viruses with envelopes and viruses without envelopes?

Since viral gene expression is regulated by the same machinery as host cell gene expression, which of the following is most likely involved in regulating expression of bacteriophage genes?

Use the figures to answer the question. Which of the three types of viruses shown would you expect to have glycoproteins among its components?

Which of the following correctly describes the viral assembly process?

Use the figures to answer the question. Which of the three types of viruses shown in the figure would you expect to include a capsid(s) ?

The virus genome and viral proteins are assembled into virus particles during which of the following parts of the reproductive cycle?

Viruses can carry out which of the following processes?

Which of the following characteristics is typical of the lytic cycle of a bacteriophage?

Which of the following statements accurately describes the lysogenic cycle of lambda (λ) phage?

What is the function of reverse transcriptase in retroviruses?

Which of the following characteristics correctly describes retroviruses?