Unit4 Study Questions - Virology Flashcards
Viral genomes vary greatly in size and may include from four genes to several hundred genes. Which of the following viral features is most apt to correlate with the size of the genome?
A) size of the viral capsomeres B) RNA versus DNA genome C) double- versus single-strand genomes D) size and shape of the capsid E) glycoproteins of the envelope
D - size and shape of the capsid
Viral envelopes can best be analyzed with which of the following techniques?
A) transmission electron microscopy
B) antibodies against specific proteins not found in the host membranes
C) staining and visualization with the light microscope
D) use of plaque assays for quantitative measurement of viral titer
E) immunofluorescent tagging of capsid proteins
B - antibodies against specific proteins not found in the host membranes
The host range of a virus is determined by
A) the enzymes carried by the virus.
B) whether its nucleic acid is DNA or RNA.
C) the proteins in the host’s cytoplasm.
D) the enzymes produced by the virus before it infects the cell.
E) the proteins on its surface and that of the host.
E - the proteins on its surface and that of the host
Most human-infecting viruses are maintained in the human population only. However, a zoonosis is a disease that is transmitted from other vertebrates to humans, at least sporadically, without requiring viral mutation. Which of the following is the best example of a zoonosis?
A) rabies B) herpesvirus C) smallpox D) HIV E) hepatitis virus
A - rabies
Which of the following accounts for someone who has had a herpesvirus-mediated cold sore or genital sore getting flare-ups for the rest of his or her life?
A) re-infection by a closely related herpesvirus of a different strain
B) re-infection by the same herpesvirus strain
C) co-infection with an unrelated virus that causes the same symptoms
D) copies of the herpesvirus genome permanently maintained in host nuclei
E) copies of the herpesvirus genome permanently maintained in host cell cytoplasm
D - copies of the herpres virus genome permanently maintained in the host nuclei
In many ways, the regulation of the genes of a particular group of viruses will be similar to the regulation of the host genes. Therefore, which of the following would you expect of the genes of the bacteriophage?
A) regulation via acetylation of histones
B) positive control mechanisms rather than negative
C) control of more than one gene in an operon
D) reliance on transcription activators
E) utilization of eukaryotic polymerases
C - control of more than one gene in an operon
Which of the following is characteristic of the lytic cycle?
A) Many bacterial cells containing viral DNA are produced.
B) Viral DNA is incorporated into the host genome.
C) The viral genome replicates without destroying the host.
D) A large number of phages are released at a time.
E) The virus-host relationship usually lasts for generations.
D - a large # of phages are released at a time
Which of the following statements describes the lysogenic cycle of lambda (λ) phage?
A) After infection, the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses.
B) Most of the prophage genes are activated by the product of a particular prophage gene.
C) The phage genome replicates along with the host genome.
D) Certain environmental triggers can cause the phage to exit the host genome, switching from the lytic to the lysogenic.
E) The phage DNA is incorporated by crossing over into any nonspecific site on the host cell’s DNA.
C- the phage genome replicate along with the host genome
Why do RNA viruses appear to have higher rates of mutation?
A) RNA nucleotides are more unstable than DNA nucleotides.
B) Replication of their genomes does not involve proofreading.
C) RNA viruses replicate faster.
D) RNA viruses can incorporate a variety of nonstandard bases.
E) RNA viruses are more sensitive to mutagens.
B - replication of their genome does not involve proofreading
Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. Which of the following observations supports this theory?
A) Viruses contain either DNA or RNA.
B) Viruses are enclosed in protein capsids rather than plasma membranes.
C) Viruses can reproduce only inside host cells.
D) Viruses can infect both prokaryotic and eukaryotic cells.
E) Viral genomes are usually similar to the genome of the host cell.
E - viral genomes are usually similar to the genome of the host cell
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?
A) The plants would develop some but not all of the symptoms of the TMV infection.
B) The plants would develop symptoms typically produced by viroids.
C) The plants would develop the typical symptoms of TMV infection.
D) The plants would not show any disease symptoms.
E) The plants would become infected, but the sap from these plants would be unable to infect other plants.
C - the plants would develop the typical symptoms of the TMV infection
Which viruses have single-stranded RNA that acts as a template for DNA synthesis?
A) lytic phages B) proviruses C) viroids D) bacteriophages E) retroviruses
E - retrovirus
What is the function of reverse transcriptase in retroviruses?
A) It hydrolyzes the host cell’s DNA.
B) It uses viral RNA as a template for DNA synthesis.
C) It converts host cell RNA into viral DNA.
D) It translates viral RNA into proteins.
E) It uses viral RNA as a template for making complementary RNA strands.
B - it uses viral RNA as a template for DNA synthesis
Which of the following describes plant virus infections?
A) They can be controlled by the use of antibiotics.
B) They are spread via the plasmodesmata.
C) They have little effect on plant growth.
D) They are seldom spread by insects.
E) They can never be passed vertically.
B - they are spread via the plasmodesmata
Which of the following represents a difference between viruses and viroids?
A) Viruses infect many types of cells, whereas viroids infect only prokaryotic cells.
B) Viruses have capsids composed of protein, whereas viroids have no capsids.
C) Viruses contain introns, whereas viroids have only exons.
D) Viruses always have genomes composed of DNA, whereas viroids always have genomes composed of RNA.
E) Viruses cannot pass through plasmodesmata, whereas viroids can.
B - viruses have capsides of protein, whereas viroids have no capsids
The difference between vertical and horizontal transmission of plant viruses is that
A) 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.
B) vertical transmission is the spread of viruses from upper leaves to lower leaves of the plant, and horizontal transmission is the spread of a virus among leaves at the same general level.
C) vertical transmission is the spread of viruses from trees and tall plants to bushes and other smaller plants, and horizontal transmission is the spread of viruses among plants of similar size.
D) vertical transmission is the transfer of DNA from one type of plant virus to another, and horizontal transmission is the exchange of DNA between two plant viruses of the same type.
E) vertical transmission is the transfer of DNA from a plant of one species to a plant of a different species, and horizontal transmission is the spread of viruses among plants of the same species.
A - 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.
What are prions?
A) mobile segments of DNA
B) tiny molecules of RNA that infect plants
C) viral DNA that has had to attach itself to the host genome
D) misfolded versions of normal brain protein
E) viruses that invade bacteria
D - misfolded versions of normal brain protein
Which of the following is the best predictor of how much damage a virus causes?
A) ability of the infected cell to undergo normal cell division
B) ability of the infected cell to carry on translation
C) whether the infected cell produces viral protein
D) whether the viral mRNA can be transcribed
E) how much toxin the virus produces
A - ability of the infected cell to undergo normal cell division
Antiviral drugs that have become useful are usually associated with which of the following properties?
A) ability to remove all viruses from the infected host
B) interference with viral replication
C) prevention of the host from becoming infected
D) removal of viral proteins
E) removal of viral mRNAs
B - interference with viral replication
Which of the following series best reflects what we know about how the flu virus moves between species?
A) An avian flu virus undergoes several mutations and rearrangements such that it is able to be transmitted to other birds and then to humans.
B) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected.
C) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans.
D) An influenza virus gains new sequences of DNA from another virus, such as a herpesvirus; this enables it to be transmitted to a human host.
E) 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, the virus mutates and can be transmitted to humans.
E - 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, the virus mutates and can be transmitted to humans.
Which of the following is the most probable fate of a newly emerging virus that causes high mortality in its host?
A) It is able to spread to a large number of new hosts quickly because the new hosts have no immunological memory of them.
B) The new virus replicates quickly and undergoes rapid adaptation to a series of divergent hosts.
C) A change in environmental conditions such as weather patterns quickly forces the new virus to invade new areas.
D) Sporadic outbreaks will be followed almost immediately by a widespread pandemic.
E) The newly emerging virus will die out rather quickly or will mutate to be far less lethal.
E - the newly emerging virus will die out rather quickly or will mutate to be far less lethal
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?
A) vaccination of all persons with preexisting cases
B) interference with new viral replication in preexisting cases
C) treatment of the HSV lesions to shorten the breakout
D) medication that destroys surface HSV before it gets to neurons
E) education about avoiding sources of infection
B - interference with new viral replication in preexisting cases
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 best fits these observations?
A) Viral capsids are needed for the cell to become infected; only the capsids enter the nucleus.
B) The viral envelope is not required for infectivity, since the envelope does not enter the nucleus.
C) Only the genetic material of the virus is involved in the cell’s infectivity, and is injected like the genome of a phage.
D) The viral envelope mediates entry into the cell, the capsid entry into the nuclear membrane, and the genome is all that enters the nucleus.
E) The viral capsid mediates entry into the cell, and only the genomic DNA enters the nucleus, where it may or may not replicate.
D - the viral envelope mediates entry into the cell, the capsid entry into the nuclear membrane and the genome is all that enters the nucleus
Which of the following characteristics, structures, or processes is common to both bacteria and viruses?
A) metabolism B) ribosomes C) genetic material composed of nucleic acid D) cell division E) independent existence
C - genetic material composed of nucleic acid
Emerging viruses arise by
A) mutation of existing viruses.
B) the spread of existing viruses to new host species.
C) the spread of existing viruses more widely within their host species.
D) mutation of existing viruses, the spread of existing viruses to new host species, and the spread of existing viruses more widely within their host species.
E) none of these.
D - mutation of existing virus, the spread of existing virus to new host species and the spread of existing viruses more widely within their host species
To cause a human pandemic, the H5N1 avian flu virus would have to
A) spread to primates such as chimpanzees.
B) develop into a virus with a different host range.
C) become capable of human-to-human transmission.
D) arise independently in chickens in North and South America.
E) become much more pathogenic.
C - become capable of human-to-human transmission
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
A) T2 protein and T4 DNA. B) T2 protein and T2 DNA. C) a mixture of the DNA and proteins of both phages. D) T4 protein and T4 DNA. E) T4 protein and T2 DNA.
D - T4 protein and T4 DNA
RNA viruses require their own supply of certain enzymes because
A) host cells rapidly destroy the viruses.
B) host cells lack enzymes that can replicate the viral genome.
C) these enzymes translate viral mRNA into proteins.
D) these enzymes penetrate host cell membranes.
E) these enzymes cannot be made in host cells.
B - host cells lack enzymes that can replicate into the viral genome
Which of the following is not a possible reservoir of infection?
A) A healthy person
B) Contaminated soil or water
C) A sick person
D) A sick animal
E) all of the above are possible reservoirs of infection
E - all of the above
Plague transmitted by a flea is an example of A) Vector transmission. B) Direct contact. C) Vehicle transmission. D) Droplet transmission. E) Fomite transmission.
A - vector transmission
Which of the following is a fomite? A) Droplets from a sneeze B) A hypodermic needle C) Water D) Pus E) Insects
B - hypodermic needle
The most frequently used portal of entry for pathogens is the
A) Mucous membranes of the respiratory tract.
B) Parenteral route.
C) Mucous membranes of the gastrointestinal tract.
D) Skin.
E) All are used equally
A - mucous membrane of the respiratory tract
Symptoms of disease differ from signs of disease in that symptoms
A) Are changes felt by the patient.
B) Always occur as part of a syndrome.
C) Are specific for a particular disease.
D) Are changes observed by the physician.
E) None of the above.
A - changes felt by the patient
The fraction of the population having a specific disease at a specific time A) incidence B) morbidity C) epidemidence D) prevalence E) prodromal rate
D - prevalence
Which of the following is the best definition of an endemic disease?
A) a disease constantly present within a population
B) a disease caused by an opportunistic pathogen
C) a disease which is increasing in incidence or prevalence
D) a disease that causes the initial illness
E) a disease present in a person from birth
A - disease constantly present within a population
Probiotics are
A) live microbial cultures of beneficial organisms
B) nutrients that encourage microbial growth
C) similar to antibiotics
D) microbial virulence factors
E) microbes that are paid to produce vitamins
A - live microbial cultures of beneficial organisms
Which of the following is true in regard to A-B toxins?
A) they are a type of endotoxin
B) they are produced only by Gram-negative organisms
C) the A subunit binds to an animal cell surface
D) the B portion is similar to LPS
E) only the A subunit is toxic
E- only the A subunit is toxic
Which of the following is not a microbial virulence factor? A) antibodies B) siderophores C) kinases D) hemolysins E) capsules
A - antibodies
Endotoxin is A) found in all Gram-negative bacteria. B) excreted from the cell. C) part of the Peptidoglycan. D) associated with gram-positive bacteria. E) also called leukocidin.
A - found in G- bacteria
