CH19 Viruses Questions

Which of the following is characteristic of the lytic cycle?

A large number of phages are released at a time.

Which replicative cycle describes a virus that can integrate its genome into the host cell's genome?

A lysogenic virus can integrate its genome into the host cell's genome and be duplicated by the host cell's replication machinery.

Why is it ineffective to treat viral disease with antibiotics? A) Antibiotics inhibit enzymes specific to bacteria and have no effect on virally encoded enzymes. B) Due to excessive antibiotic use, most viruses have evolved to be resistant to antibiotics. C) Pathogenic RNA viruses have a high rate of mutation, producing new genetic varieties that are insensitive to antibiotic treatment.

A) Antibiotics inhibit enzymes specific to bacteria and have no effect on virally encoded enzymes.

A person is most likely to recover from a viral infection if the infected cells _____. A) produce and release viral protein B) transcribe viral mRNA C) can undergo normal cell division D) can carry on translation, at least for a few hours

C) can undergo normal cell division

What are prions?

misfolded versions of normal protein that can cause disease

The host range of a virus is determined by _____.

the proteins on its surface and that of the host

What is the most effective way to stop viral infections?

vaccines Vaccines stimulate the immune system to recognize and effectively fight off invading viruses. They have proven to be the most effective weapon against viruses.

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.

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) control of more than one gene in an operon

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) not show any disease symptoms B) develop some but not all of the symptoms of the TMV infection C) develop the typical symptoms of TMV infection D) become infected, but the sap from these plants would be unable to infect other plants

C) develop the typical symptoms of TMV infection

Which of the following characteristics, structures, or processes is common to both bacteria and viruses? A) independent existence B) cell division C) genetic material composed of nucleic acid D) ribosomes E) metabolism

C) genetic material composed of nucleic acid

Which of the following can be effective in preventing the onset of viral infection in humans? A) taking antibiotics B) taking vitamins C) getting vaccinated D) taking drugs that inhibit transcription

C) getting vaccinated

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.

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

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.

As a result of the lytic cycle, _____.

The host cell's DNA is destroyed, and ultimately, the host cell itself is destroyed in the lytic cycle

Lytic cycle concludes with ________ Lysogenic cycle involves _________

The lytic cycle concludes with rupture of the host cell. The lysogenic cycle involves replication of viral DNA along with replication of the host.

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 amino acids to synthesize proteins. -They must use a host cell's ribosomes to synthesize proteins. -They must use a host cell's nucleotides for transcription and replication.

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.

Identify all correct statements about how viroids differ from viruses. Select all that apply. 1. Unlike viruses, viroids do not encode proteins. 2. Unlike viruses, the genetic material of a viroid is protein. 3. Unlike viruses, viroids cause plant disease.

1. Unlike viruses, viroids do not encode proteins. Unlike viruses, viroids do not encode proteins but can replicate in host plant cells, apparently using host cell enzymes.

How does a virus differ from a bacterium? Select all that apply. 1. Viruses are two-dimensional, whereas bacteria are three-dimensional. 2. Viruses, unlike bacteria, lack metabolic enzymes. 3. A virus, unlike a bacterium, lacks a genome.

2. Viruses, unlike bacteria, lack metabolic enzymes. Viruses lack metabolic enzymes and equipment for making proteins, such as ribosomes.

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) High mutation rate due to lack of proofreading of RNA genome replication errors.

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) Related viruses can undergo genetic recombination if the RNA genomes mix and match during viral assembly. B) The infected individuals happened to be infected with all three virus types. C) The human was likely infected with various bacterial strains that contained all three RNA viruses. D) The virus was descended from a common ancestor of bird, pig, and human flu viruses.

A) Related viruses can undergo genetic recombination if the RNA genomes mix and match during viral assembly.

Use the following information to answer the question(s) below. 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. 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) 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. B) The viral envelope is not required for infectivity, since the envelope does not enter the nucleus. C) Viral capsids are needed for the cell to become infected; only the capsids enter the nucleus. D) Only the genetic material of the virus is involved in the cell's infectivity, and is injected like the genome of a phage.

A) 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.

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 virus would be unable to reproduce within the host cell. D) The viral core proteins would not be glycosylated and might not arrive at the host plasma membrane.

A) The viral envelope proteins would not be glycosylated and might not arrive at the host plasma membrane.

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 viral genome codes for specialized enzymes not in the host. B) Viruses can stay in a quiescent state until the host cell evolves this ability. C) The virus causes mutations in the human cells, resulting in the formation of new enzymes that are capable of performing these roles. D) The virus infects only those cells and species that can perform all the replication roles necessary.

A) The viral genome codes for specialized enzymes not in the host.

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 infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium. 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 entered the bacterial cell and incorporated its DNA into the bacterial genome, allowing the bacterias cellular machinery to create new viruses.

A) The virus infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium.

Which of the following could use reverse transcriptase to transcribe its genome? A) ssRNA B) dsRNA C) ssDNA D) dsDNA

A) ssRNA

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. 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) translation rate B) replication rate C) formation of new transcription factors D) transcription rate

A) translation rate

How do prions differ from viruses? Select all that apply. 1. Unlike viruses, prions are infectious proteins. 2. Unlike viruses, prions do not include any nucleic acids. 3. Unlike a virus, a prion is a single molecule.

ALL 1. Unlike viruses, prions are infectious proteins. 2. Unlike viruses, prions do not include any nucleic acids. 3. Unlike a virus, a prion is a single molecule.

What is difference between an epidemic and a pandemic?

An epidemic is restricted to a local region; a pandemic is global.

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

B) AIDS

Which of the following events stimulates the production of viral particles in a host cell? A) Assembly of viral proteins and mRNA molecules. B) Activation of the host cell by cytokines, growth factors, or antigens. C) Processing of viral envelope proteins at the Golgi. D) Low-level transcription of viral DNA.

B) Activation of the host cell by cytokines, growth factors, or antigens. Transcription of viral DNA at low rates can occur for many years without the production of viral particles. 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.

What is the function of reverse transcriptase in retroviruses? A) It translates viral RNA into proteins. B) It uses viral RNA as a template for DNA synthesis. C) It converts host cell RNA into viral DNA. D) It uses viral RNA as a template for making complementary RNA strands.

B) It uses viral RNA as a template for DNA synthesis.

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) Replication of their genomes does not involve proofreading.

The first class of drugs developed to treat AIDS, such as AZT, were known as reverse transcriptase inhibitors. They worked because they _____. A) prevented host cells from producing the enzymes used by the virus to replicate its genome B) bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome C) bonded to the dsDNA genome of the virus in such a way that it could not separate for replication to occur D) targeted and destroyed the viral genome before it could be reverse transcribed into DNA

B) bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome

Viral infections in plants _____. A) can be controlled with antibiotics B) can spread within a plant via plasmodesmata C) are not spread by animals D) have little effect on plant growth

B) can spread within a plant via plasmodesmata

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) use the host cell to copy themselves and make viral proteins

Which of the following best reflects what we know about how the flu virus moves between species? A) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans. B) 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. C) 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) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected.

C) 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.

All of the statements below are true. Select the statement that best supports the view of most biologists that viruses are nonliving. A) The viral genome may be single-stranded or double-stranded RNA or DNA. B) Viruses are obligate intracellular parasites. C) An isolated virus is unable to replicate its genes or regenerate ATP.

C) An isolated virus is unable to replicate its genes or regenerate ATP. Viruses are unable to replicate their genes or carry out any metabolic activities outside of a host cell, and this is why most biologists do not consider viruses to be alive

What is the main structural difference between enveloped and nonenveloped viruses? A) Nonenveloped viruses have only a phospholipid membrane, while enveloped viruses have two membranes, the other one being a protein capsid. B) Enveloped viruses have their genetic material enclosed by a layer made only of protein. 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) Enveloped viruses have a phospholipid membrane outside their capsid, whereas nonenveloped viruses do not have a phospholipid membrane.

Why do scientists consider HIV to be an emerging virus? A) HIV mutates rapidly making the virus very different from HIV in the early 1980s. B) HIV infected humans long before the 1980s, but it has now mutated to a more deadly form. 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) HIV suddenly became apparent and widespread in the 1980s.

Refer to the treatments listed below to answer the following 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, 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. 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) II or III

What happens first when a phage infects a bacterial cell and is going to enter a lysogenic cycle? A) Viral DNA becomes inserted into the bacterial chromosome. B) The host cell is lysed by the invasion. C) Linear DNA circularizes. D) All bacterial descendants will carry the viral genes. E) When the bacterial chromosome replicates, viral DNA is also replicated.

C) Linear DNA circularizes. This is a true statement. This does occur at the onset of the lysogenic cycle.

Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. At its 5' end, the RNA genome has a viral protein (VPg) instead of a 5' 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) The large radioactive polypeptides are coded by the host, whereas the short ones are coded for by the virus. B) The RNA is translated into short polypeptides, which are subsequently assembled into large ones. C) The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones. D) Host cell ribosomes only translate the viral code into short polypeptides.

C) The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones. Explanation: the poliovirus would first interact with host cell vpg region to mediate translation of the RNA into a single long polypeptide, which is then cleaved into shorter ones. 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

Which of the following statements describes the lysogenic cycle of lambda (λ) phage? A) The phage DNA is copied and exits the cell as a phage. 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) After infection, the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses.

C) The phage genome replicates along with the host genome.

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 cell and acquired specific genes from the bacteria to increase the virulence of the virus. B) The virus entered the bacterial cell and incorporated its DNA into the bacterial genome, allowing the bacteria's cellular machinery to create new viruses. C) The virus infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium. D) 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 infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium.

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

C) an RNA-based lysogenic virus

To cause a human pandemic, the H5N1 avian flu virus would have to A) arise independently in chickens in North and South America. B) become much more pathogenic. C) become capable of human-to-human transmission. D) develop into a virus with a different host range. E) spread to primates such as chimpanzees.

C) become capable of human-to-human transmission.

Use the following information to answer the question(s) below. 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. 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) educate people about avoiding sources of infection B) treat HSV lesions to shorten the breakout C) interfere with new viral replication in preexisting cases of HSV D) vaccinate of all persons with preexisting cases of HSV

C) interfere with new viral replication in preexisting cases of HSV

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

C) interference with viral replication

The virus genome and viral proteins are assembled into virions (virus particles) during _____. A) the lytic cycle in all host organisms but the lysogenic cycle only in bacteria B) the lytic cycle and the lysogenic cycle in all known host organisms C) the lytic cycle only D) the lysogenic cycle only

C) the lytic cycle only

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

Which of the following processes within viral replication is the greatest source of genetic variation in RNA virus populations? A) Capsid proteins from the host cell can replace the viral capsid. B) Transcription from the host cell RNA polymerase introduces numerous mutations. C) Viral RNA is translated by host cell ribosomes. D) High mutation rate due to lack of proofreading of RNA genome replication errors.

D) High mutation rate due to lack of proofreading of RNA genome replication errors.

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) This property of HIV makes it more likely to be a pandemic than the flu virus B) Disinfecting surfaces is more important to reduce the spread of HIV than the flu C) HIV can be transmitted more easily from person to person than the flu virus D) The flu virus can be transmitted more easily from person to person than HIV

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

Which of the following supports the argument that viruses are nonliving? A) They do not evolve. B) They have RNA rather than DNA. C) Their DNA does not encode proteins. D) They are not cellular.

D) They are not cellular.

What is the source of a viral envelope?

Host cell membrane -The viral envelope is derived from host cell membrane

Which of the following represents a difference between viruses and viroids? A) Viruses have genomes composed of RNA, whereas viroids have genomes composed of DNA. B) Viruses cannot pass through plasmodesmata, whereas viroids can. C) Viruses infect many types of cells, whereas viroids infect only prokaryotic cells. D) Viruses have capsids composed of protein, whereas viroids have no capsids.

D) Viruses have capsids composed of protein, whereas viroids have no capsids.

Which of the following accounts for someone who has had regular herpesvirus-mediated cold sore or genital sore flare-ups? A) re-infection by the same herpesvirus strain B) re-infection by a closely related herpesvirus of a different strain C) copies of the herpesvirus genome permanently maintained in host cell cytoplasm D) copies of the herpesvirus genome permanently maintained in host nuclei

D) copies of the herpesvirus genome permanently maintained in host nuclei

Refer to the treatments listed below to answer the following 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, 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. 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) either I or IV

To make a vaccine against mumps, measles, or rabies, which type of viruses would be useful? A) dsDNA viruses B) dsRNA viruses C) positive-sense ssRNA viruses D) negative-sense ssRNA viruses

D) negative-sense ssRNA viruses

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 A) a mixture of the DNA and proteins of both phages. B) T2 protein and T4 DNA. C) T4 protein and T2 DNA. D) T2 protein and T2 DNA. E) T4 protein and T4 DNA.

E) T4 protein and T4 DNA.

RNA viruses require their own supply of certain enzymes because A) host cells rapidly destroy the viruses. B) these enzymes translate viral mRNA into proteins. C) these enzymes penetrate host cell membranes. D) these enzymes cannot be made in host cells. E) host cells lack enzymes that can replicate the viral genome.

E) host cells lack enzymes that can replicate the viral genome. Explanation: RNA viruses have RNA as genetic material whereas the host cells usually have DNA as genetic material. So, in order to integrate its genome with host DNA, the virus must form DNA from RNA, that is, reverse transcription. It is the process by which DNA is formed using RNA as a template strand. However, reverse transcriptase (enzyme which catalyzes reverse transcription) is usually not present in host cells. Thus, RNA viruses carry their own set of enzymes which help in the replication of viral genome and its recombination with host DNA as host cells lack these enzymes.

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.

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.

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.

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.

How do enveloped viruses differ from nonenveloped viruses?

They have a membrane-like outer covering surrounding their capsid

Why are retroviruses considered a special class of viruses?

They transcribe RNA to DNA using reverse transcriptase.

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

capsid

What do we call a virus that attacks a bacterium?

phage or bacteriophage

Double-stranded viral DNA is incorporated into a host cell as a _____.

provirus "Provirus" is the name given to double-stranded viral DNA that has been incorporated into a host cell's genome.

Viral DNA makes mRNA by the process of _____.

replication Viral DNA co-opts the cell's reproductive machinery.

A virus consisting of a single strand of RNA, which is transcribed into complementary DNA, is a _____.

retrovirus

Which viruses have single-stranded RNA that acts as a template for DNA synthesis?

retroviruses

The lytic cycle of bacteriophage infection ends with the _____.

rupture of the bacterium The bacterium ruptures and phages are released

The genetic material of HIV consists of _____.

single-stranded RNA -The genetic material of HIV consists of two molecules of single-stranded RNA.

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

strain