CH 26: Viruses

Prions are A) strands of nucleic acids encased in a protein coat. B) viral nucleic acids integrated into the host chromosomes. C) viral-infected cells. D) infectious proteins with no associated nucleic acid. E) proteins coded by genes.

D. infectious proteins with no associated nucleic acid.

Recently a class of infectious proteins with no associated nucleic acid have been identified. They are referred to as A) bacteriophages. B) latent viruses. C) viroids. D) prions. E) virions.

D. prions

While they are simple relative to cells, viruses often have a very diverse collection of components. Which one of the following choices is least likely to be found as part of a virus? A) proteins with functional binding sites B) membrane components C) single-stranded DNA D) ribosomes E) glycoproteins

D. ribosomes

Plasma from a sick mouse is filtered across a membrane that has a 200 nm pore size. If the filtrate is still infectious if injected into a healthy mouse, then the pathogen is most likely a(n): A) bacterium B) archaean C) fungus D) virus E) parasitic worm

D. virus

Which of the following statements about the types and subtypes of the influenza (flu) virus is FALSE? A) Of the three major types of flu virus (A, B, and C), only Type A can occur in humans, other mammals, and birds. B) Flu subtype is determined by the kinds of proteins representing the H and N protein spikes making up the capsid of the virus. C) The A(H2N2) and the A(H3N2) strains of the virus require different vaccines. D) High mutation rates create more diversity in strains of flu than does genetic recombination. E) Genetic recombination between influenza and other types of viruses is common.

E) Genetic recombination between influenza and other types of viruses is common.

What kind of pathogen would retain its ability to cause infections after being treated with powerful proteolytic chemicals that would destroy all proteinaceous material? A) A virus B) A prion C) A fungus D) A bacterium E) A viroid

E. A viroid

Which of the following statements about bacteriophage is false? A) Bacteriophages do not have a viral envelope. B) A temperate phage can have its DNA integrated into the host chromosome as a prophage. C) Ultraviolet radiation can cause induction. D) A prophage is replicated with the bacterial chromosome and passed to the two new daughter cells. E) Late genes are only expressed during the lysogenic cycle.

E. Late genes are only expressed during the lysogenic cycle.

Which of the following statements about emerging viruses is FALSE? A) Emerging viruses are able to "jump" from one species to another. B) Hantavirus, which causes a hemorrhagic-type fever, originates in deer mice. C) Ebola is an emerging virus of unknown origins that can have a mortality rate in excess of 50%. D) The emerging virus SARS is a coronavirus. E) The stable genome of the SARS virus makes it an unlikely candidate for vaccine development.

E. The stable genome of the SARS virus makes it an unlikely candidate for vaccine development.

Benign Vibrio cholerae becomes pathogenic by all of the following steps except A) a bacteriophage introduces a gene coding for the cholera toxin. B) the cholera toxin gene is incorporated into the benign Vibrio cholerae chromosome. C) the benign host is transformed into a disease-causing agent by the toxin. D) the cholera toxin gene is translated. E) a bacteriophage binds only to benign Vibrio cholerae without pili.

E. a bacteriophage binds only to benign Vibrio cholerae without pili.

Viruses infect every organism that has been investigated for their presence. However, viruses can only replicate in A) very limited conditions, depending on their capsid type. B) a very limited manner if they are a retrovirus. C) a very limited manner depending on their envelope capability with the host's cell membrane or cell wall. D) their lytic stage outside the host cell membrane. E) a very limited number of the host's cells.

E. a very limited number of the host's cells.

Each HIV particle possesses a ___________ on its surface, called gp120, that precisely binds to a protein, called CD4, that is found on the surfaces of the immune system cells called macrophages and T cells. A) nucleic acid B) phospholipid C) polysaccharide D) glycolipid E) glycoprotein

E. glycoprotein

One way in which retroviruses differ from all other types of viruses is that retroviruses A) possess an RNA genome. B) possess only single-stranded nucleic acids. C) can create a prophage. D) have single-strained RNA that serves as viral mRNA. E) have the enzyme reverse transcriptase.

E. have the enzyme reverse transcriptase.

Mad cow disease is caused by a A) bacterium. B) virus. C) viroid. D) virion. E) prion.

E. prion

Outside the protein sheath, many viruses have a(n) ________ made of protein, lipid, and carbohydrate.

ENVELOPE

Tetracycline is effective against viruses because it disrupts the action of the viral ribosomes.

FALSE

Nucleotide analogs are a class of drugs that are highly effective against many types of viruses. They work by halting the replication of viral genes. They are equally effective at stopping the spread of prion diseases.

False

Retroviruses are unique because they are a combination of RNA and DNA

False

Viruses are self-replicating but the replication is much faster in a host cell.

False

________ infects the CD4+ T cells, which are required for normal immunity.

HIV

The switch from a lysogenic prophage to a lytic cycle is called A) transformation. B) induction. C) latency. D) phage conversion. E) injection.

B. INDUCTION

Which of the following statements about TSEs (transmissible spongiform encephalopathies) is FALSE? A) TSEs include scrapie in sheep, mad cow disease, chronic wasting disease in deer and elk, and kuru and variant Creutzfeldt-Jakob disease in humans. B) The incidence of Creutzfeldt-Jakob disease in humans increased after an outbreak of mad cow disease in England, suggesting that mad cow disease may be transmitted to humans. C) Viroids are the likely cause of TSEs. D) TSEs do not seem to be affected by treatments that would eliminate nucleic acid-based diseases. E) Infectious TSE preparations do not seem to contain DNA or RNA.

C. Viroids are the likely cause of TSEs.

Can a virus be killed? A) Yes, destroying its genome kills it. B) No, viruses are capable of self-assembly and cannot be permanently killed. C) Yes, separating the genes from the capsid kills it. D) No, viruses are nonliving and cannot die.

D. No, viruses are non-living and cannot die.

Diseases such as scrapie in sheep, "mad cow" disease in cattle, and Creutzfeldt-Jakob disease in humans are known as A) viroids. B) viruses. C) retroviruses. D) TSEs (transmissible spongiform encephalopathies). E) emerging viruses, for example Ebola.

D. TSEs (transmissible spongiform encephalopathies).

Phages are viruses that can infect A) humans. B) plants. C) insects. D) farm animals. E) bacteria.

E. bacteria

Which of the following would not be a component of a newly produced HIV virus? A) protein capsid B) RNA C) reverse transcriptase D) viral envelope E) complementary DNA

E. complementary DNA

Viruses are ________ -coated fragments of DNA or RNA.

PROTEIN

Viruses can ________ only after they have entered a host cell, and only by using the host's cellular machinery.

REPRODUCE

A ________ can contain DNA or RNA as its genetic material, but not both.

VIRUS

The pneumonia caused by the influenza virus results from the accumulation of fluid and cell debris in the lungs. This occurs during the lysogenic life cycle of the virus.

false

Viruses may cause cancer in these three typical ways: A) Some viruses encode an oncogene in their genome. B) A viral genome may integrate into the host chromosome, disrupting a cell cycle gene. C) Some viral proteins interact with cell cycle regulatory proteins. D) Viral infection provides large amounts of nutrients, encouraging the cell to divide and proliferate. E) All viruses promote host cell proliferation, as a way to spread more virus. F) Cell proliferation is an adaptive response of the host to any viral infection, to outgrow the virus. G) When a DNA virus brings extra DNA into the host cell, that signals that S phase is complete.

triggering the expression of cancer-causing genes present in the genome.

Vibrio cholerae lives in water and gets the genes to produce a toxin from a virus (phage conversion). The toxin kills the intestinal epithelial cells in the human host resulting in massive diarrhea. Untreated cholera has about a 50% mortality rate. How does killing humans help the bacteria? A) Diarrhea helps the bacteria to spread from person to person. B) Killing humans provides nutrients for the bacteria. C) They don't -- humans are not the main host and their symptoms are maladaptive for the bacteria. D) The bacteria reproduce faster in a dead human.

A) Diarrhea helps the bacteria to spread from person to person.

The specific white blood cells that HIV attaches to are the ____________ cells. A) CD4+ B) gp120-T C) CCR5-T D) CXCR4-T E) CD8-T

A. CD4+

An experimental chemical has been shown to selectively cleave phosphodiester bonds. How would the affect a virus? A) Fragment the genome B) Digest the capsid C) Dissociate the envelope D) Alter the host binding site E) Hydrolyze the protein coating

A. Fragment the genome

Which of the following is a unique feature of viruses that separates them from bacteria? A) They are generally smaller. B) They are often highly toxic. C) They lack proteins. D) They have different nucleotides in their hereditary material. E) They cannot exist outside of a host cell.

A. They are generally smaller.

The onset of AIDS is often accompanied by A) a steep drop in T cell numbers. B) macrophage infection. C) a positive HIV test. D) lung infections and other opportunistic infections. E) Kaposi's sarcoma.

A. a steep drop in T cell numbers.

If the gp120 glycoprotein were damaged as a result of a mutation, HIV would have difficulty: A) binding to a host cell. B) leaving a macrophage. C) inserting its genes into the host cell's genome. D) assembling the capsid. E) attaching its RNA to a host cell's ribosome.

A. binding to a host cell

What is the name for parasitic viral DNA that has been integrated into the chromosome of its bacterial host? A) prophage B) prophase C) viroid D) virion E) arbovirus

A. prophage

Most viruses form a capsid around their nucleic acid core. This capsid is composed of A) proteins. B) monosaccharides. C) glycoproteins. D) lipoproteins.

A. proteins

All of the following are diseases caused by viruses except A) strep throat. B) AIDS. C) polio. D) small pox. E) measles.

A. strep throat

A scientist is studying the lysogenic cycle of the lambda 1 phage of Escherichia coli. This means that she is investigating A) the integration and stabilizing of the lambda 1 phase into a host cell's genome. B) the integration of the bacteria's genome with the viral genome outside of the bacteria's cell wall. C) the integration of the viral genome into the ribosomes present in the bacteria to direct protein synthesis for the capsid formation. D) the integration and stabilizing of a virus into its capsid, which provides protection until conditions are better for reproduction.

A. the integration and stabilizing of the lambda 1 phase into a host cell's genome.

The direction of genetic information transfer in a retrovirus (such as HIV) is A) DNA to mRNA to protein. B) RNA to DNA to mRNA to protein. C) DNA to protein. D) RNA to mRNA to protein. E) RNA to protein.

B. RNA to DNA to mRNA to protein.

An example of an "emerging virus" (a virus in a new host) with a lethality rate in excess of 50% is A) influenza virus. B) Ebola virus. C) hepatitis B. D) variola virus. E) yellow fever.

B. ebola virus

HIV infects cells by recognizing the cell-surface markers with its own A) DNA. B) glycoproteins. C) reverse transcriptase. D) capsid protein. E) enzymes.

B. glycoproteins

The HIV virus is considered a(n) ______ virus, because after getting integrated into the host cell chromosomes, it does not begin replicating immediately. A) phage B) latent C) transforming D) benign E) inducible

B. latent

Scientists have demonstrated that the cholera bacteria, Vibrio cholerae, can exist as a rather harmless form or, by phage conversion, can exist as a disease-causing, virulent form. This conversion is caused by A) the phage entering the cholera bacterium genome and causing the bacterium's cell to lyse. B) the phage introducing a gene into the bacterium's chromosome that codes for the cholera toxin that can cause death in humans. C) the phage altering the cell wall of the cholera bacterium that produces a toxin that can cause death in humans. D) the phage alters the host cell, which permits direct entry of the cholera bacterium into the host cell leading to death in humans.

B. the phage introducing a gene into the bacterium's chromosome that codes for the cholera toxin that can cause death in humans.

What best describes whether a virus is likely to infect a particular cell? A) Viruses infect the first cells they encounter. B) If a host cell is weakened, viruses are likely to infect it. C) A virus will only infect host cells with the correct surface receptors. D) Viruses only attack epithelial cells, such as the cells lining the lungs. E) The initial choice is random but once a cell type is chosen it becomes the preferred host.

C) A virus will only infect host cells with the correct surface receptors.

A doctor's office has run out of the latest flu vaccine, but many patients are asking for it. One of the nurses finds some vials from last year's batch in a refrigerator. Should they be used? A) Yes, because the preservatives and refrigeration ensure that the vaccine is still fresh. B) No, because each year the technology to make a good vaccine improves. C) No, because each year the vaccine is made against different subtypes of the flu virus. D) Maybe - the vaccine should be mixed in a test tube with the virus to see if it still inactivates it.

C) No, because each year the vaccine is made against different subtypes of the flu virus.

A mutation in the gene encoding the integrase enzyme renders the protein non-functional. How would the affect the HIV infection cycle? A) The gp120 glycoprotein would not be able to bind the CCR5 receptor. B) Reverse transcription would not be possible. C) The viral DNA would not be able to integrate the viral genome into a chromosome. D) Cutting and assembling the capsid would be halted.

C) The viral DNA would not be able to integrate the viral genome into a chromosome. Formation of the provirus would be stopped.

Once a prophage is present in a bacterial genome, viral genes are reproduced every time the bacterium multiplies. Expression of viral genes, however, is inhibited by a repressor protein. Cell stress can induce the formation of proteases that degrade the repressor. What will result? A) The virus will enter the lysogenic cycle. B) The bacterium will reject the viral genes. C) The virus will enter the lytic cycle. D) The bacterial genome will be denatured.

C) The virus will enter the lytic cycle.

Which class of drugs would be effective against HIV but not against most other pathogenic viruses? A) Nucleotide analogs that halt replication. B) Receptor antagonists that block viral entry. C) Non-nucleoside reverse transcriptase inhibitors that block reverse transcription. D) Translation inhibitors that stop assembly of viral proteins.

C. Non-nucleoside reverse transcriptase inhibitors that block reverse transcription.

Integrase inhibitors work by: A) Agglutinating the reverse transcriptase inhibitors B) Degrading the viral envelope C) Preventing the incorporation of the viral DNA into the genome D) Blocking the final viral assembly

C. Preventing the incorporation of the viral DNA into the genome

Which of the following is a virus with an icosahedral head, a capsid that contains primarily three proteins, a connecting neck with a collar and long whiskers, a long tail and a complex base plate? A) influenza virus B) measles virus C) T4 bacteriophage D) HIV E) tuberculosis

C. T4 bacteriophage

Viruses are characterized by all of the following except A) being found in every organism investigated so far. B) being specific to the hosts they infect. C) being capable of independent reproduction. D) being acellular.

C. being capable of independent reproduction.

Virulent viruses multiply within infected cells and eventually A) cause an alternation of generations in the host cell, releasing new viruses. B) cause the transformation of the host cell, releasing new viruses. C) cause lysis of the host cell, releasing new viruses. D) cause the transduction of the host cell, releasing new viruses. E) cause a transfer of material from the host cell, releasing new viruses.

C. cause lysis of the host cell, releasing new viruses.

Nearly all viruses are constructed of A) DNA with a protein wrapping, called a capsid. B) RNA with a protein wrapping, called a capsid. C) either DNA or RNA with a protein wrapping, called a capsid. D) either DNA or RNA, however many do not have the capsid.

C. either DNA or RNA with a protein wrapping, called a capsid.

A layer of lipoprotein and glycoprotein that covers the outer surface of some viruses is the A) capsid. B) casing. C) envelope. D) membrane. E) viroid.

C. envelope

All of the following are part of phage conversion except A) injection of phage gene into host. B) transcription and translation of phage gene. C) induction of phage. D) expression of phage gene by host. E) integration of phage gene to form a prophage.

C. induction to phage

If a virus enters the lytic phase in a host's cell, it will cause the host cell to A) reject the virus. B) shrink because of the loss of cytoplasm that has been used in the synthesis of viral DNA. C) lyse due to the action of enzymes. D) replicate itself at a higher than normal frequency. E) initiate an attack on the virus.

C. lyse due to the action of enzymes

Viruses that become established as stable parts of the host cell genome are called A) lethal. B) potent. C) temperate. D) virulen

C. temperate

The enormous genetic diversity of HIV has made it especially difficult to create a vaccine against the virus. This genetic diversity is largely the result of A) mutation hotspots in the hemagglutinin (H) molecule. B) mutation hotspots in the CD4+ molecule. C) the high error rate of reverse transcriptase. D) the high sensitivity of the virus to UV radiation.

C. the high error rate of reverse transcriptase.

The SARS virus is a member of the family of viruses called ________.

CORONAVIRUS

Gardasil is marketed as a cervical cancer vaccine but it is actually a human papilloma virus vaccine. Why is this done? A) The virus multiplies more rapidly in cancerous cells. B) Cancer cells are particularly susceptible to viral infection. C) Genital warts is a sign of cancer. D) HPV in the cervical epithelial cells may cause the cells to become cancerous.

D) HPV in the cervical epithelial cells may cause the cells to become cancerous.

The infection cycle of HIV includes all of the following steps except A) attachment. B) entry. C) replication. D) immediately killing the host cell. E) viral DNA integrates into the host chromosome.

D. immediately killing the host cell.