Deck 3: Virus Classification: the World of Viruses

Question 1

According to the RNA World hypothesis,which of the following enzymes may have evolved first?

A)DNA-dependent RNA polymerase
B)DNA-dependent DNA polymerase
C)RNA-dependent RNA polymerase
D)RNA-dependent DNA polymerase
E)self-replicating RNAs

Answer 1

E

Question 2

Which of the following is a type of nucleic acid NOT found as the genome of a virus that can infect vertebrates?

A)ssDNA
B)dsDNA
C)ssRNA
D)dsRNA
E)All of the above are found.

Answer 2

E

Question 3

Which of the following characteristics are NOT one of the most important criterion used to classify viruses into families?

A)topology of genome (linear or circular)
B)strandedness of genome (double or single stranded)
C)type of nucleic acid used in genome (DNA or RNA)
D)structure of virion
E)species of host infected

Answer 3

E

Question 4

What is a ribozyme?

A)A molecule of RNA that is independently capable of replicating without cellular enzymes.
B)A molecule of RNA that codes for an enzyme.
C)Another name for a small infectious molecule of RNA
D)A virus that uses a small piece of RNA as its genome.
E)A molecule of RNA that can carry out an enzymatic process.

Question 5

The advantage of using a helical instead of an icosahedral nucleocapsid to package a ssRNA genome is…..

A)it is more efficient to envelope a helical nucleocapsid than an icosahedral capsid.
B)it is easier to produce a helical nucleocapsid than an icosahedral capsid.
C)it better protects the genome from degradation inside the cell.
D)it requires a smaller protein to build than an icosahedral capsid.
E)it requires fewer copies of the nucleocapsid protein than an icosahedral capsid.

Question 6

What distinguishes a satellite virus from a satellite nucleic acid?

A)A satellite virus encodes its own capsid protein while a satellite nucleic acid does not.
B)A satellite virus packages its own replication protein while a satellite nucleic acid does not.
C)A satellite virus requires a helper virus while a satellite nucleic acid does not.
D)Genomes of satellite viruses are smaller than those of satellite nucleic acids.
E)Satellite viruses do not encode any proteins while satellite nucleic acids do.

Question 7

The family classification scheme for DNA bacteriophages is not very useful for describing the evolutionary relationships between these viruses.What is the best explanation for this?

A)DNA bacteriophages can infect more than one host species.
B)DNA bacteriophages have a wide variety of virion structures.
C)The viral genomes are genetic mosaics due to recombination.
D)There are too many bacteriophages to classify into families.
E)These viruses do not have an evolutionary relationship to each other.

Question 8

The name of a virus family in the Latin classification system has which of the following endings?

A)-viridae
B)-virales
C)-virinae
D)-virus
E)-virusdae

Question 9

Most viruses that infect plants have the following type of genome?

A)ssDNA,positive sense
B)ssDNA,negative sense
C)ssRNA,positive sense
D)ssRNA,negative sense
E)None of the above.

Question 10

An interesting observation is that many highly pathogenic and deadly human viruses have the following type of genome?

A)ssDNA,positive sense
B)ssDNA,negative sense
C)ssRNA,positive sense
D)ssRNA,negative sense
E)dsRNA

Question 11

Almost all of the viruses with positive-strand RNA genomes and enveloped virions infect which group of hosts?

A)Bacteria.
B)Vertebrates
C)Plants
D)Fungi
E)Algae.

Question 12

According to the RNA World hypothesis,which of the following subcellular entities may have evolved first?

A)Retroviruses
B)RNA Viruses
C)Viroids
D)DNA Viruses
E)Bacteriophages

Question 13

What is a possible explanation for why ssDNA viruses have genomes less that 10kb in size?

A)ssDNA is not as physically stable as dsDNA.
B)ssDNA is not transcribed by host cells.
C)ssDNA can form hairpin structures because of base-pairing.
D)Larger pieces of ssDNA can not be replicated.
E)Larger pieces of ssDNA can not easily enter the host cell.

Question 14

There are several types of viruses with enveloped virions that can infect plants.

Question 15

Which of the following virus families contains viruses with the longest ssRNA genomes?

A)Picornaviruses
B)Coronaviruses
C)Flaviviruses
D)Togaviruses
E)Bromoviruses

Question 16

There are a number of small DNA viruses that are highly dependent on their host cells for transcription and replication enzymes.Which of the following could explain the evolutionary origins of these viruses?

A)They originated from fragments of the genomes of larger more independent viruses.
B)They originated from intracellular plasmids found in bacteria.
C)They originated from the genomes of intracellular organelles,such as mitochondria.
D)They originated from fragments of cellular DNA that broke away from the cell genome.
E)All of the above could be correct.

Question 17

What is approximately the largest size of a double-stranded DNA genome of a virus that infect vertebrates?

A)25 kbp.
B)50 kbp
C)100 kbp
D)300 kbp
E)500 kbp

Question 18

Which of the following types of genomes is most commonly found in viruses that can infect fungi?

A)ssDNA
B)dsDNA
C)ssRNA
D)dsRNA
E)All of the above are found.

Question 19

Which of the following virus families have the ability to synthesize reverse transcriptase?

A)Retroviruses
B)Caulimoviruses
C)Hepadnaviruses
D)None of the above are correct.
E)All of the above are correct.

Question 20

Which of the following may be a factor in explaining why viral ssRNA genomes are not usually as long as the dsDNA genomes?

A)It is much more difficult to package a large ssRNA genome into a capsid.
B)Long ssRNA molecules form too many secondary structures that inhibit replication.
C)Long RNA genomes are difficult to translate.
D)Long RNA genomes are difficult to transcribe.
E)Long pieces of RNA are easily broken by mechanical damage.

Question 21

Why is the type of disease caused not the best criteria to use when classifying a virus?

Question 22

Mimivirus,which infects an amoeba,is the largest known dsDNA virus and has a genome larger than some free living bacteria and archae.Even though it encodes many of its own enzymes and even tRNAs,it still does not produce its own ribosomes.Describe the possible evolutionary origin of such a large and complex viruses.

Question 23

Viroids do not require a helper virus in order to replicate and cause disease.

Question 24

Retroviruses are the only virus family known to package two copies of its genome.