Deck 14: Viruses

Question 1

Which of the following statements about viruses is INCORRECT?

A) Viruses are obligate parasites.
B) The basic composition of a virus is a genome surrounded by a protective layer.
C) Viruses are not cells.
D) Viruses range in size from approximately 25-200µm.
E) All of the answers are correct.

Answer 1

Viruses range in size from approximately 25-200µm.

Question 2

A virion is defined as

A) another common term for a virus.
B) Latin for 'contagious fluid'.
C) a very small virus.
D) the inert, transmission stage of a virus.
E) the reproductive, metabolically active stage of a virus.

Answer 2

the inert, transmission stage of a virus.

Question 3

All viruses consist of

A) genome.
B) lipoprotein envelope.
C) DNA or RNA.
D) protective coat.
E) protein.

Answer 3

lipoprotein envelope.

Question 4

A number of seminal experiments by plant pathologists on tobacco infected with tobacco mosaic virus (TMV) established the principle of the existence of viruses. Which of the following were NOT techniques used to help establish the existence of viruses?

A) Precipitation of infective agents with ethanol that retained infectivity
B) Culturing of small particles
C) The ability of infective agents to be passed through a porcelain filter with pores too small to permit bacteria to pass through them
D) Sap from diseased plants could infect non-diseased plants
E) Diffusion of infective agents from sap into a block of gelatin

Question 5

Molecular biological techniques have developed with the study of viruses. One such technique used to help confirm the existence of viruses was

A) clarified sap of infected plants was used to produce novel antigens in rabbits after exposure.
B) birefringence was observed in sap after it was cooled and sonicated.
C) novel antibodies were created by rabbits exposed to sap from plants infected with tobacco mosaic virus.
D) treated sap produced a polarisation of light that suggested spherical or dodecahedral shaped particles.
E) All of the options listed are correct.

Question 6

Why has the study of viruses been integral to the development of molecular biology?

A) Because viruses were only able to be visualised in detail with the invention of the electron microscope.
B) Only molecular biology techniques were able to discern that viruses are little more than DNA in a protein coat.
C) Viruses are not living entities, thus they could not be studied using traditional experiments that microscopic and sub-microscopic organisms responded to.
D) Because organisms were not well understood at the molecular level until molecular biological techniques revealed the true nature and complexity of genes, chromosomes and proteins.
E) All the options listed here are correct.

Question 7

You are studying an unknown virus and note that upon contact with a specific host, the virus's terminal tail fibres attach and the outer layer twists and contracts. This forces the core of the virus's tail through the host's cell membrane such that the viral genome enters the host. Based on this information, the host for this virus must be a

A) plant.
B) animal.
C) bacteria.
D) fungi.
E) the virus could infect any host.

Question 8

Which of the following does NOT occur when a virion infects a suitable host?

A) The host cell carries out new virus production.
B) The virion starts to replicate its genome using a viral polymerase II.
C) The viral genome is inserted into the host cell.
D) The genome of the virion diverts the metabolism of the host cell.
E) The virion disassembles either partly or wholly.

Question 9

Viral genomes can take several forms. Which of the following is NOT a type of genome that can be found in a viral cell?

A) dsDNA
B) combination of both DNA and RNA
C) dsRNA
D) ssDNA
E) ssRNA

Question 10

What is the correct definition of a viral genome?

A) The minimum set of genes required for cellular metabolism.
B) All of the potential genes that can make up a virus.
C) The dsDNA or ssDNA component of a virus, excluding RNA.
D) The minimum set of genes required to cause infection.
E) The minimum set of genes required to cause infection plus coat protein.

Question 11

A retrovirus has a ssRNA genome. When it enters a host its genome is transcribed and incorporated into the host genome. As such, its replication strategy from infection through to the creation of new viral particles must be

A) ssRNA - dsDNA.
B) ssRNA - dsDNA - ssDNA.
C) ssRNA - dsDNA - ssRNA.
D) ssRNA - ssDNA - ssRNA.
E) ssRNA - ssDNA.

Question 12

Why are many retroviruses also associated with an increased risk of cancer?

A) Because their process of genome replication can interfere with normal host genome function.
B) Because they carry oncogenes within their genomes that can be transferred into the hosts genome.
C) Because they encode for enhancers that promote the expression of endogenous oncogenes.
D) Because reverse transcriptase can turn itinerant endogenous transcripts into DNA that can incorporate back into the hose genome.
E) All the options listed here are potentially correct.

Question 13

When a virion comes into contact with a suitable host cell, the virus switches to its reproductive phase which consists of

A) enzyme denaturation.
B) coat protein degradation.
C) lipoprotein envelope hydrolysis.
D) metabolic inertia.
E) metabolically active genes.

Question 14

Which of the following is an example of a virus with one of the smallest known genomes, and what is the genome's approximate size?

A) Tobacco mosaic virus, genome of approximately 6000 nucleotides
B) Poxvirus, genome of approximately 20,000 nucleotides
C) Lambda phage, genome of approximately 4000 nucleotides
D) AIDS, genome of approximately 10,000 nucleotides
E) Potato Y potyvirus, genome of approximately 8000 nucleotides

Question 15

In a retrovirus, what is the role of the reverse transcriptase enzyme?

A) Transcribes ssRNA into dsDNA
B) Transcribes ssDNA into dsDNA
C) Transcribes dsDNA into ssRNA
D) The direct translation of viral genomic material into protein
E) It converts host transcripts into viral genome virions

Question 16

Which of the following is an example of a retrovirus?

A) Human immunodeficiency virus (HIV)
B) Cauliflower mosaic virus
C) T4 phage
D) Lambda phage
E) Hepatitis B

Question 17

Which of the following statements in relation to the genome of a virus is CORRECT?

A) Some viruses have divided genomes in separate packages.
B) Viruses do not have circular genomes.
C) A viral genome is always packaged within a single, infectious virion.
D) Like all living organisms, viral genomes are composed of DNA.
E) Viruses copy their own genomes before using their hosts cellular machinery to produce proteins and assemble new viral particles.

Question 18

In the biochemical life cycle of a virus, which phase follows immediately after the transmission phase?

A) Reproductive
B) Infectious
C) Inert
D) Processing
E) Packaging

Question 19

After the genes of a virus use a host's metabolic systems to produce proteins and DNA, what is formed once the replicated viral genomes and viral proteins finish assembling?

A) Virions
B) Lipoprotein envelopes
C) Virus coats
D) Cell lysis proteins to facilitate the release of newly created viral particles
E) Viral genomes

Question 20

An unknown virus is being studied in a molecular biology lab. A scientist deduces that in order for this virus to replicate after infecting a suitable host cell, it must use a replicase complex that includes both viral and host proteins. Based on this, the scientist is able to determine that this virus must have a genome comprised of

A) ssDNA.
B) ssRNA.
C) dsRNA.
D) dsDNA.
E) Insufficient information is given to determine the type of genome.

Question 21

A retrovirus is defined as

A) a virus with an RNA genome that replicates by inserting DNA into a host's genome.
B) a virus with a DNA genome that replicates by inserting DNA into a host's genome.
C) a virus with a DNA genome that replicates by inserting RNA into a host's genome.
D) a virus with a RNA genome that replicates by inserting RNA into a host's genome.
E) any of a group of viruses that can cause cancer.

Question 22

A virus with a plus-stranded genome can be

A) translated directly from subgenomic mRNAs.
B) attenuated after being chemically deproteinised.
C) translated only after a complimentary reading strand is synthesised.
D) identified via light microscopy.
E) transcribed from genomic ssDNA.

Question 23

A virus with a negatively stranded genome has its genome chemically extracted from a virion. Why is this genome NOT contagious?

A) Because it is no longer associated with viral proteins
B) Because the genome must first be transcribed into a plus strand
C) Because chemical extraction shears nucleic acids
D) Because it is not incorporated into a suitable host genome
E) Because negative strands are non-transmissible

Question 24

Which of the following statements in relation to viral replication is INCORRECT?

A) Viruses may mix their genetic material to produce new combinations.
B) Viral genes can incorporate into a host's genome and remain dormant for extended periods.
C) In mixed infections, viral genomes may recombine.
D) Viruses reproduce asexually.
E) Viral replication is uniform in nature.

Question 25

When a retrovirus infects a suitable host cell, what is transcribed to produce progeny ssRNA genomes?

A) ssDNA
B) dsDNA
C) ssRNA
D) dsRNA
E) ssRNA and/or ssDNA

Question 26

You have extracted total protein from a mutant virus that lacks any a specific enzyme activity, and discover that the extract contains several very large proteins. You compare this to a similar extract taken from a wild-type population of the same species and discover there are no very large proteins, but you do observe additional smaller peptides. How can you explain this result?

A) Polyproteins are evident in the mutant extract.
B) The mutant lacks the ability to hydrolyse the long proteins.
C) The w/t virus was able to produce protein degrading enzymes.
D) A viral encoded protease was functional in the w/t population but not in the mutant.
E) All the options listed here are correct.

Question 27

Most viruses are transmitted by

A) faecal contamination.
B) pollen or seed.
C) vectors.
D) milk.
E) water.

Question 28

A human population is struck down by a viral epidemic resulting in a high percentage of mortality. Virologist one argues that this is most likely due to the virus having mutated, while virologist two contends that the virus has switched hosts. Which virologist is most likely to be correct and why?

A) Virologist A, even though viruses have low rates of mutation due to error checking polymerase enzymes.
B) Virologist B, as host switching occurs commonly in nature.
C) Both hypotheses are probably wrong, as neither mutation nor host switching is likely to result in a virulent outbreak.
D) Virologist A, as host switching is always associated with a wild population and a human population.
E) Both hypotheses are equally plausible as both mutation and host switching can result in virulent outbreaks.

Question 29

A previously unknown virus is discovered in an isolated population of mammals. Several mammals are found to be infected with the virus but display few symptoms. Based on this observation, the mammal population is likely to have been exposed to this virus

A) for a long time, as several mammals are found to be infected.
B) for a short time, as the virus has not yet evolved enough to make the hosts seriously ill.
C) for a long time, as the hosts have developed resistance and/or the virus has low virulence.
D) for a short time, as the viral infection has not had enough time to produce symptoms in the infected hosts.
E) for an indeterminate length of time. The information provided does provide any evidence either way.

Question 30

Which of the following is NOT an example of how a virus can aid its own dispersal?

A) Nutrient diversion from ovaries instead used to greatly increase pollen production, to faciliate the dispersal of a pollen borne plant virus.
B) Increased CO₂ output of infected hosts to attract additional viral vectors.
C) Fever in hosts infected with viruses that are mosquito borne.
D) Coughing and sneezing of mammalian hosts to produce airborne, contaminated droplets.
E) Plant virus causing discolouration to attracts more viral vectors.

Question 31

Viruses are polyphyletic. From this term, you can accurately conclude that viruses have independently evolved how many times?

A) More than once
B) Once
C) Twice
D) More than twice
E) Unknown

Question 32

Why is there no universal phylogenetic tree joining all viruses, like those that exist for other organisms?

A) Because viruses are not organisms
B) Many viruses remain uncharacterised, meaning not enough data has been collated to produce such a tree
C) Because the diseases they cause are so varied, they are difficult to classify
D) There is no single gene shared by all viruses
E) Many viruses do not have dsDNA genomes, therefore very few have true genes from which to build a phylogenetic tree

Question 33

A virus is isolated independently from two infected individuals. Each individual shows similar symptoms. Under an electron microscope, both viruses share common morphological features. Based on this information, what would you predict in relation to their respective nucleotide sequences?

A) The two viruses are clearly of the same species, therefore they would have identical genomes.
B) They may be the same, slightly different or substantially different. The high rate of mutation in viruses makes large genome differences common.
C) Quite different, as shared symptoms and morphology do not necessarily correlate to nucleotide conservation.
D) As many viruses do not have DNA, nucleotide differences or similarities are irrelevant.
E) They would be the same, or may differ slightly.

Question 34

The best definition of a virus species is a

A) self-perpetuating nucleotide fragment.
B) obligate host-dependant parasitic entity.
C) viral lineage that occupies a particular ecological niche.
D) virion or virions requiring a suitable replicating environment.
E) conserved nucleotide sequences, sharing commonality in hosts, symptoms and reproductive processes.

Question 35

Which of the following is least likely to be a shared feature of a viral genus or group?

A) Host specificity
B) Biochemical life cycles
C) Method of dispersal
D) Replication strategy
E) Structure and composition of virions

Question 36

When comparing different viral species, some genes can be clearly identified as being related due to their sequence similarity, which indicates a common lineage between two species. However, in some instances other genes can also be found that are completely unrelated and thus contradict evidence of shared ancestry. Such observations could be explained by

A) viral conjugation.
B) inactive polymerase error checking mechanisms.
C) different host specificities between viral species.
D) recombination events occurring within viruses across the species barrier.
E) All options listed here are correct.

Question 37

Under what specific conditions is a satellite virus able to replicate?

A) When it has infected a suitable host cell
B) When a helper virus is present with the satellite virus in a suitable host cell
C) When it is within the vicinity of a specific helper virus
D) When its host is immunosuppressed
E) When a helper virus and satellite nucleic acids are all present in a suitable host cell

Question 38

How are satellite nucleic acids transmitted?

A) Via a living vector
B) By droplet transmission
C) Satellite nucleic acids are not contagious and therefore not transmitted
D) Within the genome of a helper virus
E) Within the virions of a helper virus

Question 39

A scientist has identified a repetitive sequence of DNA from a mammalian species that appears to move around its genome. If this sequence were found to have nucleotide similarities to viruses, it is likely to be a

A) transposon.
B) retrovirus.
C) retrotransposon.
D) satellite virus.
E) replicon.

Question 40

You are working in a molecular virology laboratory, studying a diseased tropical plant. You identify a circular ssRNA genome that is 350 nucleotides in length. No other viruses are infecting the plant. Which of the following statements in relation to these observations is CORRECT?

A) The genome demonstrates it can reproduce in the host, therefore it is a viroid.
B) The genome demonstrates it can reproduce in the host, therefore it is a virus.
C) The genome demonstrates it can reproduce in the host, therefore it is a satellite virus.
D) The genome demonstrates it can NOT reproduce in the host, therefore it is a viroid.
E) The genome demonstrates it can NOT reproduce in the host, therefore it is a virus.

Question 41

A proteinaceous infectious particle is also known as a

A) prion.
B) virus.
C) viroid.
D) privoid.
E) virion.

Question 42

Which of the following is NOT a method employed to control the spread of viruses?

A) Antibiotics
B) Destruction of infected hosts
C) Washing hands
D) Use of condoms during intercourse
E) Mosquito net

Question 43

A seriously ill child has presented to Emergency at a hospital. He is showing symptoms of cerebral dysfunction, anxiety, confusion and agitation. The only clue as to the origins of the illness is that the child has been recently handling fruit bats. The first doctor to examine the child suspects the bat was a host for a viral infection, while the second suspects the child has been bitten by mites from the bats.
Which doctor's treatment should be given priority based on the information provided?

A) The second doctor, as mites are common vectors of animal diseases.
B) The first doctor, as mites do not cause disease.
C) The first doctor, as fruit bats are common carriers of viral infections such as rabies.
D) The second doctor, as treating mites is far simpler and quicker than treating a virus.
E) Both doctors are incorrect in their speculations.

Question 44

Why is a viral infection difficult to control via biochemical means without harming the host?

A) Because they are very small.
B) Because their genomes can be so variable.
C) Because they recombine so readily, they often contain sequences homologous with their hosts. Therefore if these sequences are targeted, the host is also damaged.
D) Because viruses employ their hosts biochemical systems to reproduce.
E) Because they do not respond to antibiotics.

Question 45

Which of the following can be used as an effective vaccine against viral disease?

A) Injection with virions of a non-virulent strain
B) Injection with virions 'disarmed' by formaldehyde treatment
C) All of the options listed here are correct
D) Injection with virion proteins obtained biochemically
E) Injection with virion proteins obtained by transgenic modification