Question 1

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

Accepted Answer

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

Question 2

Which of the following characteristics, structures, or processes is common to both bacteria and viruses?

Accepted Answer

A)  metabolism 
B)  ribosomes 
C)  genetic material composed of nucleic acid 
D)  cell division

Question 3

Which of the following correctly describes a strategy that bacteria have evolved to defend against infection by phage?

Accepted Answer

A)  The CRISPR-Cas system allows bacteria to recognize phage strains that have previously infected that bacterial lineage and targets the phage DNA for destruction. 
B)  Bacteria secrete enzymes that diffuse away from the cell and digest phage capsid proteins so the virus cannot infect the cells. 
C)  Bacteria methylate phage DNA as it enters the cell, targeting it for destruction by restriction enzymes. 
D)  The lysogenic cycle allows bacteria evolve inhibitors that bind with the phage DNA they contain so their daughter cells will no longer be infected.

Question 4

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?

Accepted Answer

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.

Question 5

Viruses require host cell's machinery to make copies of themselves. However, some viruses that infect humans require mechanisms that do not normally occur in human cells. Which of the following describes how the viruses can replicate in human cells?

Accepted Answer

A)  The virus causes mutations in the human cells, resulting in the formation of new enzymes that are capable of performing these roles. 
B)  The viral genome codes for specialized enzymes not found in the host cells. 
C)  The virus can enter these cells but new viruses will not be made until an environmental change triggers a switchover. 
D)  Viruses can stay in a quiescent state until the host cell evolves this ability.

Question 6

Which of the following viruses would most likely contain reverse transcriptase?

Accepted Answer

A)  an RNA-based lytic virus 
B)  an RNA-based lysogenic virus 
C)  a DNA-based lytic virus 
D)  a DNA-based lysogenic virus

Question 7

Azidothymidine (AZT) is a reverse transcriptase inhibitor that was part of the first class of antiviral drugs developed to treat HIV infection. Which of the following correctly describes how these drugs inhibited HIV infection?

Accepted Answer

A)  The drugs targeted and destroyed the viral genome before it could be reverse transcribed into DNA. 
B)  The drugs bonded to the viral dsDNA and prevented it from being able to be used as a template for replication. 
C)  The drug bonded to the viral reverse transcriptase enzyme and prevented it from making a DNA copy of viral RNA. 
D)  The drugs prevented host cells from producing the enzymes used by the virus to replicate its genome.

Question 8

Which of the following statements correctly describes a difference between viruses and prions?

Accepted Answer

A)  Viruses infect many types of cells, whereas prions infect only prokaryotic cells. 
B)  Viruses have protein capsids surrounding nucleic acids, whereas prions are made only of nucleic acids. 
C)  Viruses have genomes composed of RNA, whereas prions have genomes composed of DNA. 
D)  Viruses replicate using its host's DNA replication machinery, whereas prions replicate using host's translation machinery.

Question 9

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?

Accepted Answer

A)  DNA replication rate 
B)  mRNA splicing 
C)  translation rate 
D)  formation of new transcription factors

Question 10

A person is most likely to recover from a cold due to viral infection if the infected cells are able to perform which of the following processes?

Accepted Answer

A)  normal cell division 
B)  absorption of antibiotics 
C)  production and release viral protein 
D)  transcription of viral mRNA

Question 11

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

Accepted Answer

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

Question 12

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?

Accepted Answer

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.

Question 13

Viruses can carry out which of the following processes?

Accepted Answer

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.

Question 14

An infectious substance capable of causing disease in plants is isolated and researchers want to determine whether the substance is a bacterium or a virus. Which of the following methods will best allow them to determine the type of infectious agent they have isolated?

Accepted Answer

A)  Treat the substance with enzymes that destroy all nucleic acids, and then determine whether the substance is still infectious. 
B)  Culture the substance with plant cells, and then determine whether the cells lyse. 
C)  Treat the sample with proteases that digest all proteins, and then determine whether the substance is still infectious. 
D)  Culture the substance on nutritive medium, away from any plant cells.

Exam 26: Introduction to Viruses