Chapter 19: Viruses Bio Test

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

AIDS

Vaccine

A harmless variant or derivative of a pathogen that stimulates a host's immune system to mount defenses against the pathogen

Prophage

A phage genome that has been inserted into a specific site on the bacterial chromosome.

Virulent phage

A phage that replicates only by a lytic cycle.

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

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.

Restriction enzymes

An endonuclease (type of enzyme) that recognizes and cuts DNA molecules foreign to a bacterium (such as phage genomes). The enzyme cuts at specific nucleotide sequences (restriction sites).

Reverse transcriptase

An enzyme encoded by some certain viruses (retroviruses) that uses RNA as a template for DNA synthesis.

Which of the following is an example of vertical transmission of a virus in plants?

An infected plant produces seeds that contain the virus, giving rise to infected progeny.

Prion

An infectious agent that is a misfolded version of a normal cellular protein. Prions appear to increase in number by converting correctly folded versions of the protein to more prions.

How do prions, which are misfolded proteins, infect organisms?

Prions enter brain cells and cause normal forms of the protein to refold into the prion form.

What is the function of reverse transcriptase in retroviruses?

It uses viral RNA as a template for DNA synthesis.

How does a retrovirus like HIV enter a host cell?

Glycoproteins on the viral envelope bind to receptors on the host cell. The viral envelope fuses with the host cell's plasma membrane, facilitating uptake of the virus by the host cell.

Which of the three types of viruses shown would you expect to include glycoproteins?

II only

Reverse transcription, carried out by retroviruses, is the process by which __________.

RNA information is copied into DNA

When comparing DNA and RNA viruses, which mutate more quickly, and why?

RNA viruses, because no proofreading is done on RNA molecules

How are retroviruses different from other types of viruses?

Retroviruses use the enzyme reverse transcriptase to transcribe a copy of DNA from their own RNA.

Coronavirus: Economic Contribution

Stock market rise in face masks and stocks in China are decreasing due to the virus and fear of products carrying the virus.

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?

The cells can undergo normal cell division.

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?

The viral envelope proteins would not have glycoproteins added to them and might not arrive at the host plasma membrane.

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?

The plants would develop the typical symptoms of TMV infection.

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

Vaccines are inactive versions of a virus that stimulate an immune reaction in a person.

Which of the following descriptions correctly identifies the main structural differences between viruses with envelopes and viruses without envelopes?

Viruses with envelopes have a phospholipid membrane outside their capsid, whereas viruses without envelopes do not have a phospholipid membrane.

Which of the following processes can viruses carry out?

They can use the host cell to copy themselves and make viral proteins.

Why are retroviruses considered a special class of viruses?

They transcribe RNA to DNA using reverse transcriptase.

Viruses that infect bacteria are called __________.

bacteriophages

A population of viruses with similar characteristics is called a ________.

class

Pandemic

a global epidemic

In many ways, the regulation of the genes of a particular group of viruses will be similar to the regulation of the host genes. Therefore, which of the following regulation mechanisms would you expect of the genes of a bacteriophage?

control of more than one gene in an operon

Temperate phage

a phage that is capable of replicating by either a lytic or lysogenic cycle

The avian flu virus H5N1 is considered a greater long-term threat than the swine flu virus H1N1 because __________.

it has a significantly higher mortality rate

A phage that inserts itself into the host DNA is called __________.

lysogenic

The phage reproductive cycle that kills the bacterial host cell is a __________ cycle, and a phage that always reproduces this way is a __________ phage.

lytic; virulent

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

getting vaccinated to certain viruses

Vaccines for viral diseases are __________ and help prevent infection by __________.

harmless derivatives of pathogenic viruses; stimulating the immune system to mount a defense against the actual pathogen

In the figure, at the arrow marked II, what enzyme is being utilized?

host cell DNA polymerase

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

interference with viral replication

Animals that harbor and can transmit a particular virus but are generally unaffected by it are said to act as a __________ for that virus.

natural reservoir

Which of the following is not a class I virus?

parvovirus

All of the following types of viruses have envelopes except __________.

picornovirus

Candidates for the original source of viral genomes include __________.

plasmids and transposons

Viral DNA incorporated into a bacterial chromosome is known as a(n) __________.

prophage

Genomes of viruses may consist of which of the following types of nucleic acids?

single RNA or DNA Double RNA or DNA

Class IV viruses are characterized by which of the following types of genomes?

single-stranded RNA that serves as mRNA

The virus genome and viral proteins are assembled into virus particles during which of the following parts of the reproductive cycle?

the lytic cycle only

Coronavirus: Math Contribution

the number of cases are rising and have over 35,000 people infected and over 100 people have died from it.

Which of the following characteristics is typical of the lytic cycle of a bacteriophage?

A large number of phages are released at a time.

Epidemic

A widespread outbreak of an infectious disease.

Retrovirus

An RNA virus that replicates by transcribing its RNA into DNA and then inserting the DNA into a cellular chromosome; an important class of cancer-causing viruses.

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

Replication of their genomes does not involve proofreading.

Why do scientists consider HIV to be an emerging virus?

HIV suddenly became apparent and widespread in the 1980s.

Why can flare-ups of herpes virus infection recur throughout a person's life?

Herpes virus can leave its DNA behind as minichromosomes in the nerve cell nuclei. Stress can trigger another round of virus production, producing characteristics blisters and sores.

Which of the three types of viruses shown in the figure would you expect to include a capsid(s)?

I, II, and III

What happens first when a phage infects a bacterial cell and is going to enter a lysogenic cycle?

Linear DNA circularizes.

Cornavirus: Culture Contribution

Lunar New Year was not a big celebration in Asia and there's racism towards asian/chinese people due to the virus.

Some viruses have membranous envelopes. Where do viral envelopes typically originate from?

Membranes from the host cell

Will treating a viral infection with antibiotics affect the course of the infection?

No; antibiotics work by inhibiting enzymes specific to bacteria. Antibiotics have no effect on eukaryotic or virally encoded enzymes.

When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm?

Only the nucleic acid

How do prions propagate and replicate themselves?

Prions convert normal proteins into the misfolded prion version.

Coronavirus: Scientific Contribution

Some symptoms would be pneumonia, sore throat, cough, etc. Transmission can be through what you touch and from another person.

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?

The drug molecules bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome.

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?

The flu virus can be transmitted more easily from person to person than HIV

Which of the following events occurs during the lytic life cycle of phages?

The host cell usually dies, releasing many new copies of the virus.

Which of the following statements accurately describes the lysogenic cycle of lambda (λ) phage?

The phage genome is integrated in the host chromosome where it is replicated along with the host genome.

A plant that has been raised in a sterile environment shows symptoms of a viral infection. How would you explain this?

The viral infection was acquired by vertical transmission.

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?

The viral genome codes for specialized enzymes not found in the host cells.

Which of the following statements supports the argument that viruses are nonliving?

They do not carry out metabolic processes.

Which of the following characteristics correctly describes retroviruses?

They have a single-stranded RNA that acts as a template for DNA synthesis.

Why are viruses called obligate intracellular parasites?

They must use a host cell's metabolic enzymes and pathways to obtain energy. They must use a host cell's ribosomes to synthesize proteins. They must use a host cell's amino acids to synthesize proteins. They must use a host cell's nucleotides for transcription and replication. All of the above.

Which of the following statements correctly describes one difference between virulent phages and temperate phages?

Virulent phages replicate through the lytic cycle only, and temperate phages replicate using both the lytic and lysogenic cycles.

Why are viruses often considered to be nonliving?

Viruses do not carry out metabolic processes, a primary characteristic of living organisms.

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

Viruses generally cause disease symptoms quickly, whereas prions generally take many years to cause disease symptoms.

Bacteriophage

a type of virus that attacks only bacteria

Prions are __________ that are thought to cause disease by __________.

abnormally shaped proteins; inducing similar but normally shaped proteins in the brain to adopt the abnormal form

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

an RNA-based lysogenic virus

The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?

capsid

Which of the following events or characteristics accounts for someone who has had regular herpesvirus-mediated cold sores or genital sore flare-ups?

copies of the herpesvirus genome permanently maintained in host nuclei

Restriction enzymes help defend bacteria against viral infections by __________.

cutting viral DNA once it has entered the cell

A widespread outbreak of a viral disease is called a(n) __________, and a global outbreak is called a(n) __________.

epidemic; pandemic

In the figure, when new viruses are being assembled at the point marked IV, what mediates the assembly?

no mediator is required; the new viruses self-assemble

What do we call a virus that attacks a bacterium?

phage

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

retrovirus

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

ssRNA

Viruses can vary with respect to all of the following characteristics except __________.

the presence or absence of metabolic machinery

capsid

the protein shell of a virus

The host range of a virus is determined by _____.

the proteins on its surface and that of the host

HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because __________.

the virus binds to specific receptors that are only present on certain immune cells

Some viruses can be crystallized and their structures analyzed. One such virus is yellow mottle virus, which infects beans. This virus has a single-stranded RNA genome containing about 6,300 nucleotides. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. If the yellow mottle virus begins its infection of a cell by using its genome as mRNA, which of the following would you expect to be able to measure when analyzing the reproduction of this virus?

translation rate

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

transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant

HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template?

vaccines

Circular RNA molecules that function like a virus in plants are termed __________.

viroids