Question 1

Which of the following statements is correct regarding viral infections in plants?
A) They can be controlled with antibiotics.
B) They can spread within a plant via plasmodesmata.
C) They have little effect on plant growth.
D) They are not spread by animals.

Accepted Answer

Viral infections in plants can spread within a plant from cell to cell via plasmodesmata, which are channels between adjacent cells. Antibiotics are not effective against viral infections in plants, and these infections can have significant negative effects on plant growth. While animals can spread some plant viruses, many are spread via insects or other vectors.

Question 2

What are prions?
A) mobile segments of DNA
B) tiny circular molecules of RNA that can infect plants
C) viral DNA that attaches itself to the host genome and causes disease
D) misfolded versions of normal proteins that can cause disease

Accepted Answer

Prions are misfolded proteins that can cause disease. They are not mobile segments of DNA, tiny circular molecules of RNA, or viral DNA that attaches itself to the host genome.

Question 3

Which of the following statements correctly describes a difference between viruses and prions?
A) Viruses infect many types of cells, whereas prions infect only prokaryotic cells.
B) Viruses have capsids composed of protein, whereas prions are made only of nucleic acid.
C) Viruses have genomes composed of RNA, whereas prions have genomes composed of DNA.
D) Viruses generally cause disease symptoms quickly, whereas prions generally take many years to cause disease symptoms.

Accepted Answer

Viruses often cause symptoms soon after infection, while prions, which are misfolded proteins, can take years to cause symptoms as they gradually accumulate in the brain.

Question 4

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 can incorporate a variety of nonstandard bases.
D) RNA viruses are more sensitive to mutagens.

Accepted Answer

Replication of RNA genomes does not involve proofreading. RNA polymerases lack the proofreading ability of DNA polymerases and therefore make more mistakes during replication. This results in a higher rate of mutations in RNA viruses.

Question 5

Which of the following statements best reflects what we know about how the flu virus moves between species?
A) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected.
B) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans.
C) 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.
D) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates, the virus is passed to a new species such as a bird, and the virus mutates again and can now be transmitted to humans.

Accepted Answer

Genetic recombination is a common way for flu viruses to move from one species to another. Pigs are particularly good hosts for the flu virus because they can be simultaneously infected with multiple strains of flu. When this happens, the different strains of virus can exchange genetic material and form a new virus that can infect a new species, such as a bird or a human. This process is called reassortment and can lead to the emergence of new flu strains that can cause pandemics.

Question 6

Refer to the treatments listed to answer the question.
You isolate an infectious substance capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, or prion. You have four methods at your disposal to analyze the substance and determine the nature of the infectious agent.
I.Treat the substance with enzymes that destroy all nucleic acids, and then determine whether the substance is still infectious.
II.Filter the substance to remove all elements smaller than what can be easily seen under a light microscope.
III.Culture the substance on nutritive medium, away from any plant cells.
IV.Treat the sample with proteases that digest all proteins, and then determine whether the substance is still infectious.
If you already know that the infectious agent was either bacterial or viral, which method(s) listed above would allow you to distinguish between these two possibilities?
A) I
B) II
C) II or III
D) IV

Accepted Answer

Filtering the substance (II) would remove viruses, which are smaller than bacteria, while culturing on a nutritive medium (III) would allow bacteria to grow but not viruses, which require a host cell.

Question 7

Effective antiviral drugs are usually associated with which of the following properties?
A) interference with viral replication
B) prevention of the host from becoming infected
C) removal of viral proteins
D) removal of viral mRNAs

Accepted Answer

Effective antiviral drugs usually work by interfering with viral replication, which means they target specific steps in the viral life cycle to prevent the virus from reproducing and spreading in the host. This can help to reduce the severity and duration of viral infections. Prevention of host infection, removal of viral proteins, and removal of viral mRNAs are not typical properties associated with antiviral drugs.

Question 8

Which of the following processes can be effective in preventing the onset of viral infection in humans?
A) taking vitamins before being exposed to various viruses
B) getting vaccinated to certain viruses
C) taking antibiotics to inhibit bacterial growth
D) taking drugs that inhibit transcription

Accepted Answer

Getting vaccinated to certain viruses is the only option that can effectively prevent the onset of viral infection in humans. Vitamins, antibiotics, and drugs that inhibit transcription do not have the same effectiveness in preventing a viral infection.

Question 9

Viruses use the host cell's machinery to make copies of themselves. However, some human viruses require a type of replication that humans do not normally have. For example, humans normally do not have the ability to convert RNA into DNA. How can these types of viruses infect humans, when human cells cannot perform a particular role that the virus requires?
A) The virus causes mutations in the human cells, resulting in the formation of new enzymes that are capable of performing these roles.
B) The viral genome codes for specialized enzymes not found in the host cells.
C) The virus infects only those cells and species that can perform all the replication roles necessary.
D) Viruses can stay in a quiescent state until the host cell evolves this ability.

Accepted Answer

Some viruses, such as retroviruses, carry enzymes like reverse transcriptase that allow them to convert their RNA genome into DNA, which can then integrate into the host cell's genome. These specialized enzymes are not commonly found in human cells but are coded for by the virus itself, allowing it to complete its replication cycle.

Question 10

The first class of antiviral drugs developed to treat HIV infection, such as AZT, were known as reverse transcriptase inhibitors. How did these drugs carry out their functions?
A) The drugs targeted and destroyed the viral genome before it could be reverse transcribed into DNA.
B) The drug molecules bonded to the dsDNA genome of the virus in such a way that it could not separate for replication to occur.
C) The drug molecules bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome.
D) The drugs prevented host cells from producing the enzymes used by the virus to replicate its genome.

Accepted Answer

Reverse transcriptase inhibitors, such as AZT, work by binding to the viral reverse transcriptase enzyme and preventing it from making a DNA copy of the viral RNA genome. This prevents the virus from replicating and spreading throughout the body.

Question 11

If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins in the Golgi apparatus, which of the following processes could likely result?
A) The viral envelope proteins would not have glycoproteins added to them and might not arrive at the host plasma membrane.
B) The viral capsid proteins would not have glycoproteins added to them and might not arrive at the host plasma membrane.
C) The viral core proteins would not have glycoproteins added to them and might not arrive at the host plasma membrane.
D) The virus would be unable to reproduce within the host cell.

Accepted Answer

The Golgi apparatus is responsible for modifying proteins, including the addition of carbohydrates to form glycoproteins. If this process is disrupted, viral envelope proteins may not be properly glycosylated, affecting their transport to the host plasma membrane.

Question 12

A virus consisting of a single strand of RNA, which is reverse transcribed into complementary DNA, is referred to as a ________.
A) protease
B) retrovirus
C) bacteriophage
D) non-enveloped virus

Accepted Answer

The description given matches that of a retrovirus. Retroviruses, unlike most viruses that have DNA genomes, have RNA genomes that are reverse transcribed into complementary DNA, which is then integrated into the host genome.

Question 13

A person is most likely to recover from a cold due to viral infection if the infected cells are able to perform which of the following processes?
A) The cells can undergo normal cell division.
B) The cells can carry on translation, at least for a few hours.
C) The cells produce and release viral protein.
D) The cells transcribe viral mRNA.

Accepted Answer

The ability of infected cells to undergo normal cell division is important for the body to replace the infected cells with new healthy ones, leading to recovery from the cold. Translation, production and release of viral proteins, and transcription of viral mRNA all contribute to the progression of the viral infection and therefore do not promote recovery.

Question 14

Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell?
A) herpes
B) AIDS
C) smallpox
D) influenza

Accepted Answer

AIDS is caused by the human immunodeficiency virus (HIV), which is a retrovirus. Retroviruses use reverse transcriptase to transcribe their RNA genome into DNA before integrating it into the host cell's genome. This allows the virus to replicate alongside the host cell's own DNA, often leading to the development of the disease.

Question 15

HIV is inactivated in the laboratory after a few minutes of sitting at room temperature, but the flu virus is still active after sitting for several hours. What are the practical consequences of these findings?
A) HIV can be transmitted more easily from person to person than the flu virus.
B) The flu virus can be transmitted more easily from person to person than HIV.
C) This property of HIV makes it more likely to be a pandemic than the flu virus.
D) Disinfecting surfaces is more important to reduce the spread of HIV than the flu.

Accepted Answer

The flu virus can survive longer outside the body than HIV, meaning it can be transmitted more easily from person to person through contaminated surfaces or objects. This underscores the importance of frequent handwashing and disinfecting surfaces to prevent the spread of the flu virus.

Question 16

Which of the following types of viral genomes could be transcribed using reverse transcriptase?
A) ssRNA
B) dsRNA
C) ssDNA
D) dsDNA

Accepted Answer

Reverse transcriptase is an enzyme that can convert single-stranded RNA (ssRNA) into double-stranded DNA (dsDNA). Therefore, the viral genome that can be transcribed using reverse transcriptase would be ssRNA, as this enzyme is commonly found in viruses with ssRNA genomes.

Question 17

Which of the following viruses would most likely have reverse transcriptase inside them?
A) an RNA-based lytic virus
B) an RNA-based lysogenic virus
C) a DNA-based lytic virus
D) a DNA-based lysogenic virus

Accepted Answer

Reverse transcriptase is an enzyme used by retroviruses, which are RNA-based lysogenic viruses, to convert their RNA genome into DNA for integration into the host genome.

Question 18

Which of the following statements correctly describes vaccines and how they help prevent viral infection?
A) Vaccines are active versions of a virus that stimulate an immune reaction in a person.
B) Vaccines are inactive versions of a virus that stimulate an immune reaction in a person.
C) Vaccines are infectious proteins that stimulate an immune reaction in a person.
D) Vaccines are infectious enzymes that stimulate an immune reaction in a person.

Accepted Answer

Vaccines are typically made from an inactive or weakened form of a virus, which is not capable of causing disease on its own. When this vaccine is injected into a person, their immune system recognizes the foreign particle and produces a response to fight it off. This defense mechanism trains the immune system to recognize and combat the virus in the future, should the person ever be exposed to the actual virus.

Question 19

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. What would you expect to happen to the plants that were sprayed with the mixture?
A) The plants would develop some but not all of the symptoms of the TMV infection.
B) The plants would develop the typical symptoms of TMV infection.
C) The plants would not show any disease symptoms.
D) The plants would become infected, but extracts from these plants would be unable to infect other plants.

Accepted Answer

When the cell contents of nucleic acid molecules and capsomeres of TMV are left overnight and then sprayed on tobacco plants, the plants would develop the typical symptoms of TMV infection. This is because TMV capsomeres protect the viral RNA molecule and promote entry into a new host cell, leading to infection.

Question 20

The difference between vertical and horizontal transmission of plant viruses is that vertical transmission is ________.
A) transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant
B) 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) 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) 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

Accepted Answer

Vertical transmission is the transmission of a virus from a parent plant to its progeny, while horizontal transmission is the spread of the virus to another plant. The other options do not accurately describe the difference between vertical and horizontal transmission.

Quiz 19: Viruses

Which of the following statements is correct regarding viral infections in plants?

What are prions?

Which of the following statements correctly describes a difference between viruses and prions?

Why do RNA viruses appear to have higher rates of mutation?

Which of the following statements best reflects what we know about how the flu virus moves between species?

Effective antiviral drugs are usually associated with which of the following properties?

Which of the following processes can be effective in preventing the onset of viral infection in humans?

The first class of antiviral drugs developed to treat HIV infection, such as AZT, were known as reverse transcriptase inhibitors. How did these drugs carry out their functions?

If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins in the Golgi apparatus, which of the following processes could likely result?

A virus consisting of a single strand of RNA, which is reverse transcribed into complementary DNA, is referred to as a ________.

A person is most likely to recover from a cold due to viral infection if the infected cells are able to perform which of the following processes?

Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell?

HIV is inactivated in the laboratory after a few minutes of sitting at room temperature, but the flu virus is still active after sitting for several hours. What are the practical consequences of these findings?

Which of the following types of viral genomes could be transcribed using reverse transcriptase?

Which of the following viruses would most likely have reverse transcriptase inside them?

Which of the following statements correctly describes vaccines and how they help prevent viral infection?

The difference between vertical and horizontal transmission of plant viruses is that vertical transmission is ________.