Biology Ch.19 Viruses MC
Emerging viruses arise by
-the spread of existing viruses more widely within their host species. -the spread of existing viruses to new host species. -mutation of existing viruses.
28) To make a vaccine against mumps, measles, or rabies, which type of viruses would be useful? A) dsDNA viruses B) negative-sense ssRNA viruses C) positive-sense ssRNA viruses D) dsRNA viruses
B
29) 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
B
30) 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
B
31) 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. We expect that the plants would _____. A) develop some but not all of the symptoms of the TMV infection B) develop the typical symptoms of TMV infection C) not show any disease symptoms D) become infected, but the sap from these plants would be unable to infect other plants
B
32) Which of the following can be effective in preventing the onset of viral infection in humans? A) taking vitamins B) getting vaccinated C) taking antibiotics D) taking drugs that inhibit transcription
B
33) Viral infections in plants _____. A) can be controlled with antibiotics B) can spread within a plant via plasmodesmata C) have little effect on plant growth D) are not spread by animals
B
34) Which of the following represents a difference between viruses and viroids? A) Viruses infect many types of cells, whereas viroids infect only prokaryotic cells. B) Viruses have capsids composed of protein, whereas viroids have no capsids. C) Viruses have genomes composed of RNA, whereas viroids have genomes composed of DNA. D) Viruses cannot pass through plasmodesmata, whereas viroids can.
B
4) Viruses _____. A) manufacture their own ATP, proteins, and nucleic acids B) use the host cell to copy themselves and make viral proteins C) use the host cell to copy themselves and then viruses synthesize their own proteins D) metabolize food and produce their own ATP
B
43) What is difference between an epidemic and a pandemic? A) An epidemic is a disease; a pandemic is a treatment. B) An epidemic is restricted to a local region; a pandemic is global. C) An epidemic has low mortality; a pandemic has higher mortality. D) An epidemic is caused by a bacterial infection; a pandemic is caused by a viral infection
B
41) If you already know that the infectious agent was either a viroid or a prion, which method(s) listed above would allow you to distinguish between these two possibilities? A) I only B) II only C) IV only D) either I or IV
D
Lytic cycle
The lytic cycle result in the destruction of the infected cell and its membrane.
Which of the following statements describes the lysogenic cycle of lambda (λ) phage?
The phage genome replicates along with the host genome.
What is the source of a viral envelope?
The viral envelope is derived from host cell membrane.
12) What is the function of reverse transcriptase in retroviruses? A) It uses viral RNA as a template for DNA synthesis. B) It converts host cell RNA into viral DNA. C) It translates viral RNA into proteins. D) It uses viral RNA as a template for making complementary RNA strands
A
22) If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins in the Golgi, which of the following could likely result? A) The viral envelope proteins would not be glycosylated and might not arrive at the host plasma membrane. B) The viral capsid proteins would not be glycosylated and might not arrive at the host plasma membrane. C) The viral core proteins would not be glycosylated and might not arrive at the host plasma membrane. D) The virus would be unable to reproduce within the host cell
A
27) Which of the following could use reverse transcriptase to transcribe its genome? A) ssRNA B) dsRNA C) ssDNA D) dsDNA
A
3) Which of the following supports the argument that viruses are nonliving? A) They are not cellular. B) Their DNA does not encode proteins. C) They have RNA rather than DNA. D) They do not evolve
A
35) 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
A
37) A person is most likely to recover from a viral infection if the infected cells _____. A) can undergo normal cell division B) can carry on translation, at least for a few hours C) produce and release viral protein D) transcribe viral mRNA
A
38) 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
A
44) Will treating a viral infection with antibiotics affect the course of the infection? A) No; antibiotics work by inhibiting enzymes specific to bacteria. Antibiotics have no effect on eukaryotic or virally encoded enzymes. B) No; antibiotics do not kill viruses because viruses do not have DNA or RNA. C) Yes; antibiotics activate the immune system, and this decreases the severity of the infection. D) Yes; antibiotics can prevent viral entry into the cell by binding to host-receptor proteins
A
46) A population of viruses with similar characteristics is called a _____. A) strain B) species C) type D) genome
A
48) Which of the following processes within viral replication is the greatest source of genetic variation in RNA virus populations? A) High mutation rate due to lack of proofreading of RNA genome replication errors. B) Transcription from the host cell RNA polymerase introduces numerous mutations. C) Capsid proteins from the host cell can replace the viral capsid. D) Viral RNA is translated by host cell ribosomes.
A
26) A virus consisting of a single strand of RNA, which is transcribed into complementary DNA, is a _____. A) protease B) retrovirus C) RNA replicase virus D) nonenveloped virus
B
horizontal transmission
A plant is infected with a virus by an external source.
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. -Activation of the host immune cell by cytokines, growth factors, or antigens causes viral DNA to be transcribed at high rates in preparation for viral production.
17) Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. At its end, the RNA genome has a viral protein (VPg) instead of a cap. This is followed by a nontranslated leader sequence, and then a single long protein-coding region (~7000 nucleotides), followed by a poly-A tail. Observations were made that used radioactive amino acid analogues. Short period use of the radioactive amino acids result in labeling of only very long proteins, while longer periods of labeling result in several different short polypeptides. What conclusion is most consistent with the results of the radioactive labeling experiment? A) Host cell ribosomes only translate the viral code into short polypeptides. B) The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones. C) The RNA is translated into short polypeptides, which are subsequently assembled into large ones. D) The large radioactive polypeptides are coded by the host, whereas the short ones are coded for by the virus.
B
21) Which of the following viruses would most likely have reverse transcriptase? A) an RNA-based lytic virus B) an RNA-based lysogenic virus C) a DNA-based lytic virus D) a DNA-based lysogenic virus
B
23) 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
B
24) Viruses use the host'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 in the host. 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.
B
The herpes viruses are important enveloped DNA viruses that cause disease in vertebrates and in some invertebrates such as oysters. Some of the human forms are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causingchicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes aremaintained in cells in a latent phase. The virus can later reactivate, replicate again, and infect others. 42) If scientists are trying to use what they know about HSV to devise a means of protecting other people from being infected, which of the following would have the best chance of lowering the number of new cases of infection? A) vaccinate of all persons with preexisting cases of HSV B) interfere with new viral replication in preexisting cases of HSV C) treat HSV lesions to shorten the breakout D) educate people about avoiding sources of infection
B
Cycles
Bacteriophages, which contain double-stranded DNA, can reproduce by two alternative mechanisms: the lytic cycle and the lysogenic cycle. •In the lytic cycle, virus parts are made, new viruses are assembled, and the cell is lysed, releasing the newly assembled viruses. •In the lysogenic cycle, the viral DNA incorporates into the bacterial DNA and is passed on to daughter bacterial cells when the infected bacteria reproduce normally. Occasionally, an infected bacterium in the lysogenic cycle can enter the lytic cycle, in which viral particles are produced and the cell is eventually ruptured.
10) Which of the following statements describes the lysogenic cycle of lambda (λ) phage? A) After infection, the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses. B) Most of the prophage genes are activated by the product of a particular prophage gene. C) The phage genome replicates along with the host genome. D) The phage DNA is copied and exits the cell as a phage.
C
13) In the figure, at the arrow marked II, what enzyme(s) are being utilized? A) reverse transcriptase B) viral DNA polymerase C) host cell DNA polymerase D) host cell RNA polymerase
C
20) The virus genome and viral proteins are assembled into virions (virus particles) during _____. A) the lytic cycle and the lysogenic cycle in all known host organisms B) the lysogenic cycle only C) the lytic cycle only D) the lytic cycle in all host organisms but the lysogenic cycle only in bacteria
C
25) The first class of drugs developed to treat AIDS, such as AZT, were known as reversetranscriptase inhibitors. They worked because they _____. A) targeted and destroyed the viral genome before it could be reverse transcribed into DNA B) bonded to the dsDNA genome of the virus in such a way that it could not separate for replication to occur C) bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome D) prevented host cells from producing the enzymes used by the virus to replicate its genome
C
45) Why do scientists consider HIV to be an emerging virus? A) HIV infected humans long before the 1980s, but it has now mutated to a more deadly form. B) HIV mutates rapidly making the virus very different from HIV in the early 1980s. C) HIV suddenly became apparent and widespread in the 1980s. D) HIV is now starting to cause diseases other than AIDS, such as rare types of cancers and pneumonias
C
49) 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? A) The virus was descended from a common ancestor of bird, pig, and human flu viruses. B) The infected individuals happened to be infected with all three virus types. C) Related viruses can undergo genetic recombination if the RNA genomes mix and match during viral assembly. D) The human was likely infected with various bacterial strains that contained all three RNA viruses.
C
5) What is the main structural difference between enveloped and nonenveloped viruses? A) Enveloped viruses have their genetic material enclosed by a layer made only of protein. B) Nonenveloped viruses have only a phospholipid membrane, while enveloped viruses have two membranes, the other one being a protein capsid. C) Enveloped viruses have a phospholipid membrane outside their capsid, whereas nonenveloped viruses do not have a phospholipid membrane. D) Both types of viruses have a capsid and phospholipid membrane; but in the nonenveloped virus the genetic material is between these two membranes, while in the enveloped virus the genetic material is inside both membranes
C
7) Which of the following accounts for someone who has had regular herpesvirus-mediated cold sore or genital sore flare-ups? A) re-infection by a closely related herpesvirus of a different strain B) re-infection by the same herpesvirus strain C) copies of the herpesvirus genome permanently maintained in host nuclei D) copies of the herpesvirus genome permanently maintained in host cell cytoplasm
C
8) 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 would you expect of the genes of a bacteriophage? A) regulation via acetylation of histones B) positive control mechanisms rather than negative C) control of more than one gene in an operon D) reliance on transcription activators
C
9) Which of the following is characteristic of the lytic cycle? A) Viral DNA is incorporated into the host genome. B) The viral genome replicates without destroying the host. C) A large number of phages are released at a time. D) The virus—host relationship usually lasts for generations
C
Cells were infected with approximately 1000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. The intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined. 18) Using the data in the figure above, how long does it take for virus A to go through one lytic cycle? A) 15 minutes B) 30 minutes C) 45 minutes D) 90 minutes
C
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 6300 nucleotides. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. 15) 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? A) replication rate B) transcription rate C) translation rate D) formation of new transcription factors
C
You isolate an infectious substance capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, 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 determining whether the substance is still infectious. 40) 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
C
1) Which of the three types of viruses shown above would you expect to include glycoproteins? A) I only B) II only C) III only D) I and II only
D
11) Which viruses have single-stranded RNA that acts as a template for DNA synthesis? A) proviruses B) viroids C) bacteriophages D) retroviruses
D
14) In the figure, when new viruses are being assembled at the point marked IV, what mediates the assembly? A) host cell chaperones B) assembly proteins coded for by the host nucleus C) assembly proteins coded for by the viral genes D) nothing; they self-assemble
D
19) Using the data in the figure above, how long does it take for virus B to go through one lytic cycle? A) 15 minutes B) 30 minutes C) 45 minutes D) 60 minutes
D
2) Which of the three types of viruses shown above would you expect to include a capsid(s)? A) I only B) II only C) III only D) I, II, and II
D
36) 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 protein that can cause disease
D
39) Which of the following 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
D
47) Evidence suggests that factors which contribute towards the virulence of E. coli strain O157:H7, a bacterial strain reported to cause several food poisoning deaths, are caused by genes from a virus that infects bacteria. Considering this evidence, which statement most likely explains how the O157:H7 population acquired the genetic variation that distinguishes the strain from harmless E. coli strains, such as those that reside in our intestines? A) The virus entered the bacterial cell and incorporated its DNA into the bacterial genome, allowing the bacteria's cellular machinery to create new viruses. B) Viral envelope proteins bind to receptors on the bacterial membrane, allowing the viral genetic material to enter the bacterium and become translated into proteins. C) The virus entered the cell and acquired specific genes from the bacteria to increase the virulence of the virus. D) The virus infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium
D
6) The host range of a virus is determined by _____. A) the enzymes carried by the virus B) whether its nucleic acid is DNA or RNA C) the proteins in the host's cytoplasm D) the proteins on its surface and that of the host
D
The herpes viruses are important enveloped DNA viruses that cause disease in vertebrates and in some invertebrates such as oysters. Some of the human forms are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can later reactivate, replicate again, and infect others. 16) In electron micrographs of HSV infection, it can be seen that the intact virus initially reacts with cell surface proteoglycans, then with specific receptors. This is later followed by viral capsids docking with nuclear pores. Afterward, the capsids go from being full to being "empty." Which of the following best fits these observations? A) Viral capsids are needed for the cell to become infected; only the capsids enter the nucleus. B) The viral envelope is not required for infectivity, since the envelope does not enter the nucleus. C) Only the genetic material of the virus is involved in the cell's infectivity, and is injected like the genome of a phage. D) The viral envelope mediates entry into the cell, the capsid mediates entry into the nuclear membrane, and the genome is all that enters the nucleus.
D
As a result of the lytic cycle, _____.
The host cell's DNA is destroyed.
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 these binds to receptor molecules on the host cell membrane?
Glycoproteins on the viral envelope recognize and bind to receptors on the host cell.
How does HIV cause disease?
HIV kills cells that defend the body against disease. -HIV affects the immune system and kills cells that protect the body from foreign bacteria and viruses.
HIV
The human immunodeficiency virus infects cells of the human immune system. Its primary targe is a subset of lymphocytes called helper T cells, or CD4* T cells, so named because of the CD4 proteins that stud their surface.
Which enzyme inserts viral DNA into the host's chromosomal DNA?
Integrase inserts viral DNA into the host's chromosomal DNA.
What is the function of reverse transcriptase?
It catalyzes the formation of DNA from an RNA template. -This is the function of reverse transcriptase.
What happens first when a phage infects a bacterial cell and is going to enter a lysogenic cycle?
Linear DNA circularizes.
Which replicative cycle describes a virus that can integrate its genome into the host cell's genome?
Lysogenic -A lysogenic virus can integrate its genome into the host cell's genome and be duplicated by the host cell's replication machinery.
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. -Prions are a misfolded version of a protein normally found in the brain. When prions come into close proximity with the normal proteins, they cause them to refold into the prion form.
How does HIV bind to a host cell?
The viral envelope proteins interact with CD4 and a co-receptor on the cell membrane. -The viral envelope proteins gp120 and gp41 interact with CD4 and a co-receptor on the host-cell membrane.
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.
How do enveloped viruses differ from nonenveloped viruses?
They have a membrane-like outer covering. -Enveloped viruses have a membrane-like outer covering (an envelope) surrounding their capsid.
Why are viruses called obligate intracellular parasites?
They must use a host cell's nucleotides for transcription and replication. 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 metabolic enzymes and pathways to obtain energy.
Why are retroviruses considered a special class of viruses?
They transcribe RNA to DNA using reverse transcriptase.
prophage
Viral DNA incorporated into host DNA is referred to as a "prophage."
Non enveloped and enveloped virus
Viruses are classified into two major groups: nonenveloped and enveloped. •Nonenveloped viruses (a) typically exit the host cell by bursting through the plasma membrane. •Enveloped viruses (b) generally escape from the host cell by budding. Because of this, the viral envelope is often derived from the host cell's plasma membrane.
To cause a human pandemic, the H5N1 avian flu virus would have to
become capable of human-to-human transmission.
The H1N1 2009 outbreak is considered to have been which of the following?
a pandemic
Vertical transmission
a plant inherits a viral infection from a parent
Virus
a small infectious agent that replicates only inside the living cells of other organisms. Virus can infect all types of life forms, from animals and plants to bacteria and archaea.
Prions
are infections proteins that spread disease
What do we call a virus that attacks a bacterium?
bacteriophage
The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?
capsid -The protein shell that encloses a viral genome is a capsid.
Antiviral drugs that have become useful are usually associated with which of the following properties?
interference with viral replication
Pandemic
is a epidemic of infectious disease that has spread through human populations across a large region; up to worldwide
Provirus
is a genome that is integrated into the DNA of host cell.
Retrovirus
is a single stranded RNA virus that stores its nucleic acid in the form of an mRNA genome and targets a host cell as an obligate parasite.
Bacteriophage (phage)
is a virus that infects and replicates within bacteria. Bacteriophanges are composed of proteins that encapslate a DNA or RNA genome, and may have relatively simple or elaborate structures. Their genomes may encode as few as four genes and as many as hundreds of gene. Phage replicate witin bacteria following the injection of their genome into cytoplasm. Bacteriaphage are among the most common and diverse entities in the biosphere.
Integrase
is an enzyme produced by a retrovirus that enables its genetic material to be integrated into the DNA of the infected cell. (transport the transcribed DNA to the cell's DNA and integrates it) It typically lay dormant. However, if the T cells is activated by growth faters, cytokines, or antigens, the cell's transcriptional machinery increases the rate of transcription of viral DNA into messenger RNA.
Lysogenic cycle
is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome or formation of a circular replicon in the bacterium's cytoplames.The key difference between the lytic cycle and the lysogenic cycle is that the lysogenic cycle does not lyse the host cell.
Epidemic
occurs when new cases of a certain disease, in a given human population, and given a given period, substantially exceed what is expected based on recent experience.
lysing
refers to the breaking down of a cell, often by viral, ezymic, or osmotic mechanisms that compromise its integrity.
Virulent phages
replicate only by a lytic cycle.
HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template?
reverse transcription -Retroviruses are equipped with an enzyme called reverse transcriptase, which makes a DNA copy of an RNA template, providing information flow from RNA to DNA.
The lytic cycle of bacteriophage infection ends with the _____.
rupture of the bacterium
The genetic material of HIV consists of _____.
single-stranded RNA -The genetic material of HIV consists of two molecules of single-stranded RNA.
Genome
the entirety of an organism's heredity informatioin. It is encoded either in DNA or, for many type of viruses, in RNA.
Viral DNA makes mRNA by the process of _____.
transcription -Viral DNA co-opts the cell's reproductive machinery.
Temperate phages
use both lytic and lysogenic cycles.
What is the most effective way to stop viral infections?
vaccines
In the lysogenic cycle _____.
viral DNA is replicated along with host DNA -Viral DNA, incorporated into host DNA as a prophage, is replicated along with host DNA.
The pointer is indicating the _____.
viral protein coat (head)
