Viruses Q
The H1N1 2009 outbreak is considered to have been which of the following?
A pandemic
Which of the following series of events best reflects what we know about how the flu virus moves between species?
An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, and the virus mutates and can be transmitted to humans.
How do prions, which are misfolded proteins, infect organisms?
Prions enter brain cells and cause normal forms of the protein to refold into the prion form.
What is the function of reverse transcriptase in retroviruses?
It uses viral RNA as a template for DNA synthesis.
Which of the following processes can be effective in preventing the onset of viral infection in humans?
Getting vaccinated
Why do RNA viruses tend to have unusually high rates of mutation?
Replication of their genomes does not involve proofreading.
HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template?
Reverse transcription
Which of the following statements correctly describes the most probable fate of a newly emerging virus that causes high mortality in its host?
The newly emerging virus will die out rather quickly or will mutate to be far less lethal.
Which of the following statements correctly describes the lysogenic cycle of lambda (λ) phage?
The phage genome replicates along with the host genome.
A researcher lyses a cell that contains nucleic acid molecules and capsomeres of tobacco mosaic virus (TMV). The cell contents are left in a covered test tube overnight. The next day this mixture is sprayed on tobacco plants. Which of the following would be expected to occur?
The plants would develop the typical symptoms of TMV infection.
How do prions differ from viruses?
Unlike a virus, a prion is a single molecule. Unlike viruses, prions are infectious proteins. Unlike viruses, prions do not include any nucleic acids.
Which of the following statements correctly describes one difference between vertical and horizontal transmission of plant viruses?
Vertical transmission is transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant.
Most molecular biologists think that viruses originated from naked bits of cellular nucleic acid. Which of the following observations supports this theory?
Viral genomes are usually similar to the genome of the host cell.
Evidence suggests that factors which contribute towards the virulence of E. coli strain O157:H7, a bacterial strain reported to cause several food poisoning deaths, are caused by genes from a virus that infects bacteria. Considering this evidence, which statement most likely explains how the O157:H7 population acquired the genetic variation that distinguishes the strain from harmless E. coli strains, such as those that reside in our intestines?
The virus infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium
How does a virus differ from a bacterium?
Viruses, unlike bacteria, lack metabolic enzymes.
Which of the following statements accurately describes plant virus infections?
They are spread via the plasmodesmata.
What is the most effective way to stop viral infections?
Vaccines
Why are retroviruses considered a special class of viruses?
They transcribe RNA to DNA using reverse transcriptase.
Which of the three types of viruses shown in the figure would you expect to include a capsid(s) as part of their overall structure?
all three
Viral envelopes can best be analyzed with which of the following techniques?
antibodies against specific proteins not found in the host membranes
RNA viruses require their own supply of certain enzymes because __________.
host cells lack enzymes that can replicate the viral genome
Which of the following characteristics, structures, or processes is common to both bacteria and viruses?
genetic material composed of nucleic acid
In the figure, at the arrow marked II, what enzyme(s) are being utilized?
host cell DNA polymerase
Which viruses have single-stranded RNA that acts as a template for DNA synthesis?
retroviruses
Which of the following characteristics determine a virus's host range?
the proteins on its surface and that of the host
Based on the table, which virus meets the Baltimore requirements for a retrovirus?
D
Based on the table, which virus meets the requirements for a bacteriophage?
A
Which of the following statements correctly describes one characteristic of the lytic cycle of viral replication?
A large number of phages are released at a time.
The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?
Capsid
Which of the following processes within viral replication is the greatest source of genetic variation in RNA virus populations?
High mutation rate due to lack of proofreading of RNA genome replication errors.
Which of the three types of viruses shown in the figure would you expect to include glycoproteins as part of their overall structure?
I and II only
You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine the nature of the infectious agent. I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious II. filtering the substance to remove all elements smaller than what can be easily seen under a light microscope III. culturing the substance by itself on nutritive medium, away from any plant cells IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious If you already knew that the infectious agent was either bacterial or viral, which treatment would allow you to distinguish between these two possibilities?
III
What happens first when a phage infects a bacterial cell and is going to enter a lysogenic cycle?
Linear DNA circularizes.
What is a virus that attacks a bacterium?
Phage
In 2009, a flu pandemic was believed to have originated when viral transmission occurred from pig to human, thereby earning the designation, "swine flu." Although pigs are thought to have been the breeding ground for the 2009 virus, sequences from bird, pig, and human viruses were all found within this newly identified virus. What is the most likely explanation of why this virus contained sequences from bird, pig, and human viruses?
Related viruses can undergo genetic recombination if the RNA genomes mix and match during viral assembly.
A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have __________.
T4 protein and T4 DNA
The herpesviruses are very important enveloped DNA viruses that cause disease in all vertebrate species and in some invertebrates such as oysters. Some of the human ones are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can then reactivate, replicate again, and be infectious to others. In electron micrographs of HSV infection, it can be seen that the intact virus initially reacts with cell-surface proteoglycans, then with specific receptors. This is later followed by viral capsids docking with nuclear pores. Afterward, the capsids go from being full to being "empty." Which of the following statements best describes these observations?
The viral envelope mediates entry into the cell, the capsid enters into the nuclear membrane, and the genome is all that enters the nucleus.
A plant that has been raised in a sterile environment shows symptoms of a viral infection. How would you explain this?
The viral infection was acquired by vertical transmission.
Why are viruses called obligate intracellular parasites?
They must use a host cell's metabolic enzymes and pathways to obtain energy. They must use a host cell's nucleotides for transcription and replication. They must use a host cell's ribosomes to synthesize proteins. They must use a host cell's amino acids to synthesize proteins. All of the listed responses are correct.
Which of the following statements correctly describes the best predictor of how much damage a virus causes?
ability of the infected cell to undergo normal cell division
A human pandemic is __________.
an epidemic that extends around the world
The herpesviruses are very important enveloped DNA viruses that cause disease in all vertebrate species and in some invertebrates such as oysters. Some of the human ones are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can then reactivate, replicate again, and be infectious to others. In order to be able to remain latent in an infected live cell, HSV must be able to shut down what process?
apoptosis of a virally infected cell
Which of the following is why someone who has had a herpesvirus-mediated cold sore or genital sore may have flare-ups for the rest of his or her life?
copies of the herpesvirus genome remaining as mini-chromosomes in some host cell nuclei
You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine the nature of the infectious agent. I. Treat the substance with nucleases that destroy all nucleic acids and then determine whether it is still infectious. II. Filter the substance to remove all elements smaller than what can be easily seen under a light microscope. III. Culture the substance by itself on nutritive medium, away from any plant cells. IV. Treat the sample with proteases that digest all proteins and then determine whether it is still infectious. If you already knew that the infectious agent was a prion, which treatment would allow you to distinguish this?
either I or IV
The herpesviruses are very important enveloped DNA viruses that cause disease in all vertebrate species and in some invertebrates such as oysters. Some of the human ones are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can then reactivate, replicate again, and be infectious to others. If scientists are trying to use what they know about HSV to devise a means of protecting other people from being infected, which of the following would have the best chance of lowering the number of new cases of infection?
interference with new viral replication in preexisting cases
Antiviral drugs that have become useful are usually associated with which of the following properties?
interference with viral replication
Emerging viruses arise by __________.
mutation of existing viruses the spread of existing viruses to new host species the spread of existing viruses more widely within their host species All of the listed responses are correct.
In the figure, when new viruses are being assembled (IV), what mediates the assembly?
nothing; the proteins self-assemble
Which of the following responses correctly lists the order of events in a generalized viral replicative cycle?
the virus enters the cell, host enzymes replicate the viral genome, enzymes transcribe the viral genome into mRNA
