Bio 122 Chapter 19
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.
In the lysogenic cycle _____.
Viral DNA, incorporated into host DNA as a prophage, is replicated along with host DNA.
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.
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.
How does a virus differ from a bacterium?
Viruses, unlike bacteria, lack metabolic enzymes.
Which of the following viruses would most likely have reverse transcriptase inside them?
an RNA-based lysogenic virus
To cause a human pandemic, the H5N1 avian flu virus would have to
become capable of human-to-human transmission.
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
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
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
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
How do prions differ from viruses?
-Unlike viruses, prions do not include any nucleic acids. -Unlike a virus, a prion is a single molecule. -Unlike viruses, prions are infectious proteins.
Which of the following events stimulates the production of viral particles in a host cell?
Activation of the host cell by cytokines, growth factors, or antigens.
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.
What is difference between an epidemic and a pandemic?
An epidemic is restricted to a local region; a pandemic is global.
All of the statements below are true. Select the statement that best supports the view of most biologists that viruses are nonliving.
An isolated virus is unable to replicate its genes or regenerate ATP.
How do prions, which are misfolded proteins, infect organisms? See Concept 19.3 (Page 410)
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.
If this research proves correct, where is the best place to locate Klosneuvirus?
Protists
Why do RNA viruses appear to have higher rates of mutation?
Replication of their genomes does not involve proofreading.
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.
A plant that has been raised in a sterile environment shows symptoms of a viral infection. How would you explain this? See Concept 19.3 (Page 410)
The viral infection was acquired by vertical transmission.
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.
Sort the items according to whether they may be found only in free virus particles, only in uninfected host cells, or in both viruses and host cells.
Viruses only: capsid, envelope with glycoproteins, and capsomere (core protein). Host cell only: ribosome Both: DNA, RNA, and protein
Identify all correct statements about how viroids differ from viruses.
Unlike viruses, viroids do not encode proteins.
What is the most effective way to stop viral infections? See Concept 19.3 (Page 406)
Vaccines
Why are retroviruses considered a special class of viruses? See Concept 19.2
They transcribe RNA to DNA using reverse transcriptase.
Which replicative cycle describes a virus that can integrate its genome into the host cell's genome?
lysogenic
RNA viruses require their own supply of certain enzymes because
host cells lack enzymes that can replicate the viral genome
Which enzyme inserts viral DNA into the host's chromosomal DNA?
integrase
Effective antiviral drugs are usually associated with which of the following properties?
interference with viral replication
The lytic cycle of bacteriophage infection ends with the _____.
rupture of the bacterium
The host range of a virus is determined by _____.
the proteins on its surface and that of the host
Which of the following characteristics is typical of the lytic cycle of a bacteriophage?
A large number of phages are released at the same time, lysing the host cell.
Why is it ineffective to treat viral disease with antibiotics?
Antibiotics inhibit enzymes specific to bacteria and have no effect on virally encoded enzymes.
What do we call a virus that attacks a bacterium? See Concept 19.1 (Page 397)
Bacteriophages or Phage
You discover a new giant virus similar to Mimiviruses and Klosneuviruses. Where did this new virus metagenome originate?
From a viral source.
How does HIV cause disease?
HIV kills cells that defend the body against disease.
Why do scientists consider HIV to be an emerging virus?
HIV suddenly became apparent and widespread in the 1980s.
Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell?
HIV/AIDS
A new giant virus is discovered. How is it different from a regular virus?
It has genes that code for protein synthesis.
Can giant viruses synthesize proteins?
No
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.
Scientists are interested in studying the translation system genes of Klosneuvirus. Which of the following will they need in order to do this?
The host(s) that the translation system gene sequences came from.
Which of the following statements supports the argument that viruses are nonliving?
They do not carry out metabolic processes.
How do enveloped viruses differ from nonenveloped viruses?
They have a membrane-like outer covering.
What is the function of reverse transcriptase?
catalyzing the formation of DNA from a RNA template
HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template? See Concept 19.2 (Page 402)
reverse transcription
As a result of the lytic cycle, _____.
the host cell's DNA is destroyed
The pointer is indicating the _____
viral protein coat
Which of the three types of viruses shown would you expect to include glycoproteins?
2 only, The influenza virus
The H1N1 2009 outbreak is considered to have been which of the following? See Concept 19.3 (Page 407)
A pandemic
Which statements about viruses are true?
A retrovirus contains RNA, Enveloped viruses bud from the host cell, HIV contains reverse transcriptase, and the capsid enters the host cell if the virus is enveloped
The nucleic acid of a virus particle is enclosed in a protein coat. What is it called? See Concept 19.1 (Page 397)
Capsid
True or false? The human immunodeficiency virus (HIV) uses reverse transcriptase to make double-stranded RNA copies of its DNA genome.
False -A retrovirus such as HIV has an RNA genome and uses reverse transcriptase to make double-stranded DNA copies of the genome, which can then be integrated into the host cell's genome.
Which of the following processes within viral replication is the greatest source of genetic variation in RNA virus populations?
High mutation rate due to lack of proofreading of RNA genome replication errors.
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? See Concept 19.2 (Page 400)
Linear DNA circularizes.
In 2009, a flu pandemic was believed to have originated when viral transmission occurred from pig to human, thereby earning the designation, "swine flu." Although pigs are thought to have been the breeding ground for the 2009 virus, sequences from bird, pig, and human viruses were all found within this newly identified virus. What is the most likely explanation of why this virus contained sequences from bird, pig, and human viruses?
Related viruses can undergo genetic recombination if the RNA genomes mix and match during viral assembly.
A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have
T4 protein and T4 DNA
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 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 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.
How does HIV bind to a host cell?
The viral envelope proteins bind to CD4 and a co-receptor on the cell membrane
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.
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 is correct regarding viral infections in plants?
They can spread within a plant via plasmodesmata.
Which of the following processes can viruses carry out?
They can use the host cell to copy themselves and make viral proteins
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? See Concept 19.2 (Page 399)
They must use a host cell's ribosomes to synthesize proteins, metabolic enzymes and pathways to obtain energy, amino acids to synthesize proteins, and nucleotides for transcription and replication.
Viral DNA makes mRNA by the process of _____.
Transcription
Which of the following characteristics, structures, or processes is common to both bacteria and viruses?
genetic material composed of nucleic acids
The pointer is indicating the virus's _____. The figure shows a particle, which consists of two wavy strands, pointed by the arrow and with an envelope around it.
genome
Which of the following processes can be effective in preventing the onset of viral infection in humans?
getting vaccinated to certain viruses
In the figure, at the arrow marked II, what enzyme is being utilized?
host cell DNA polymerase
What is the source of a viral envelope?
host cell membrane
Classify each phrase as applying to the lytic cycle, the lysogenic cycle, or both types of reproductive cycles of phages.
lytic cycle: the host is destroyed, the cell is lysed (broken open), and new phages are assembled from viral DNA and proteins Lysogenic cycle: the viral DNA integrates into the chromosome of the host cell, the cell reproduces normally Both:viral genes are replicated
What are prions?
misfolded versions of normal protein that can cause disease
Emerging viruses arise by
mutation of existing viruses, the spread of existing viruses to new host species, and the spread of existing viruses more widely within their host species.
Double-stranded viral DNA is incorporated into a host cell as a _____.
provirus
A virus consisting of a single strand of RNA, which is reverse transcribed into complementary DNA, is referred to as a ________.
retrovirus
The genetic material of HIV consists of _____.
single-stranded RNA
Which of the following types of viral genomes could be transcribed using reverse transcriptase?
ssRNA
A population of viruses with similar characteristics is called a ________.
strain/class
Which of the following clues would tell you if a cell is prokaryotic or eukaryotic?
whether or not the cell is partitioned by internal membranes