Question 1

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

Accepted Answer

All of the above types of nucleic acids (ssDNA, dsDNA, ssRNA, dsRNA) can be found as the genome of viruses that infect vertebrates. Viruses exhibit a wide variety of genomic structures, including single-stranded DNA (ssDNA), double-stranded DNA (dsDNA), single-stranded RNA (ssRNA), and double-stranded RNA (dsRNA), all of which are known to infect vertebrate hosts.

Question 2

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

Accepted Answer

The RNA World hypothesis proposes that RNA molecules were the first self-replicating and catalytic entities before the emergence of DNA and proteins. Viroids are the smallest known infectious agents and consist only of single-stranded RNA molecules without a protein coat. Therefore, they are considered one of the most primitive forms of life and may have evolved first in the RNA World. Retroviruses and RNA viruses require a protein coat and a host cell to replicate, making them more complex and likely to have evolved later. DNA viruses and bacteriophages rely on DNA replication, which is thought to have emerged later than RNA replication.

Question 3

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

Accepted Answer

The largest known double-stranded DNA genome of a virus that infects vertebrates is the Epstein-Barr virus, which has a genome size of approximately 172 kbp. Therefore, the largest size of a double-stranded DNA genome of a virus that infects vertebrates is likely to be around 300 kbp. Choice D (300 kbp) is the closest option.

Question 4

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

Accepted Answer

Most plant viruses have a single-stranded RNA genome, which is usually positive-sense, meaning that the viral RNA can be directly translated into proteins by the host cell. Only a few plant viruses have a DNA genome, and they are usually double-stranded. Negative-sense genomes are relatively rare in plant viruses. Therefore, option C is the best choice.

Question 5

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

Accepted Answer

The correct ending for a virus family in the Latin classification system is -viridae, such as in the family Herpesviridae or Flaviviridae. The other answer choices (B) -virales, (C) -virinae, (D) -virus, and (E) -virusdae are incorrect endings for virus families.

Question 6

What distinguishes a satellite virus from a satellite nucleic acid?

Accepted Answer

A satellite virus is distinguished by its ability to encode its own capsid protein, whereas a satellite nucleic acid does not have this capability.

Question 7

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

Accepted Answer

The species of the host infected is not one of the most important criteria used to classify viruses into families. Rather, the other characteristics listed (topology, strandedness, type of nucleic acid, and structure of virion) are typically more important in determining viral classification.

Question 8

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

The answer of There are a number of small DNA...

Question 9

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

Accepted Answer

A helical nucleocapsid better protects the genome from degradation inside the cell as the RNA is completely surrounded by the protein helix, whereas only the outer surface of the RNA is in contact with the protein subunits in an icosahedral capsid.

Question 10

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

Accepted Answer

Almost all of the viruses with positive-strand RNA genomes and enveloped virions infect vertebrates. Examples include the coronaviruses, flaviviruses, and retroviruses, which cause diseases in humans and other animals. While there are some exceptions (such as the plant-infecting Tymoviridae family), the majority of these viruses infect vertebrates.

Question 11

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

Accepted Answer

Most plant viruses do not have an envelope; they are typically non-enveloped viruses. Enveloped viruses are more common in animals and humans.

Question 12

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

Accepted Answer

ssDNA is less stable than dsDNA, which limits the size of the genome that can be maintained without degradation.

Question 13

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

Accepted Answer

The RNA World hypothesis proposes that RNA was the first genetic material and that early life forms relied on self-replicating RNAs. Therefore, self-replicating RNAs, also known as ribozymes, may have evolved first in the RNA World. The other enzymes listed require DNA as a template, which suggests that they likely evolved later.

Question 14

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

Accepted Answer

Viruses that infect fungi, known as mycoviruses, most commonly have double-stranded RNA (dsRNA) genomes.

Question 15

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

The family classification scheme for DNA bacteriophages is not useful because their genomes undergo frequent recombination events, resulting in genetic mosaics that do not fit neatly into traditional taxonomic categories.

Question 16

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

Accepted Answer

Coronaviruses have the longest single-stranded RNA (ssRNA) genome among the given options, ranging from approximately 26 to 32 kilobases in length. Picornaviruses have a positive ssRNA genome with approximately 7.5 kilobases in length, Flaviviruses have a positive ssRNA genome with approximately 11 kilobases in length, Togaviruses have a positive ssRNA genome with approximately 11-12 kilobases in length, and Bromoviruses have a segmented ssRNA genome with each segment being approximately 1.4-2.2 kilobases in length.

Question 17

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

Accepted Answer

Many highly pathogenic and deadly human viruses have a single-stranded RNA (ssRNA) genome with a negative sense polarity. Examples of such viruses include Ebola virus, Lassa fever virus, and Hanta virus. These viruses require transcription of their RNA genome to produce messenger RNA that can be translated into viral proteins. The negative sense RNA genome acts as a template for the production of a complementary positive-sense RNA molecule, which then serves as the template for viral protein synthesis. The negative sense RNA genome makes it difficult for the host cell to translate the viral RNA, and as a result, these viruses often have mechanisms to overcome this obstacle, such as the use of viral polymerases or the production of viral proteins that interfere with host cell translation machinery.

Question 18

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

Accepted Answer

Retroviruses, Caulimoviruses, and Hepadnaviruses all have the ability to synthesize reverse transcriptase, which is an enzyme that transcribes RNA into DNA, a process reverse to the usual transcription. This characteristic is crucial for their replication cycle.

Question 19

What is a ribozyme?

Accepted Answer

A ribozyme is a molecule of RNA that can carry out an enzymatic process, indicating that it has catalytic activity. Unlike proteins, which are the primary catalysts in the cell, ribozymes are nucleic acid molecules that exhibit catalytic activity.

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?

Accepted Answer

The answer of Which of the following may be a...

Quiz 3: Virus Classification: The World of Viruses