Question 1

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

Accepted Answer

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 2

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?

Accepted Answer

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 3

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?

Accepted Answer

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 4

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

Accepted Answer

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

Exam 3: Virus Classification: the World of Viruses

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

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?

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?

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