- Viruses can vary with respect to all of the following characteristics except _____. (Overview) Your Answer: the presence or absence of a membranous envelope Correct Answer :the presence or absence of metabolic machinery No. This is a difference among viruses.
- A microbiologist analyzes chemicals obtained from an enveloped RNA virus that infects monkeys. He finds that the viral envelope contains a protein characteristic of monkey cells. Which of the following is the most likely explanation? (Concept 19. 1) Your Answer:Its presence is a result of the monkey's immunological response. Correct Answer:The viral envelope forms as the virus leaves the host cell. No. This does not explain the presence of either the envelope or the monkey protein found on the envelope.
- Which of the following, if any, may be a component of a virus? (Concept 19. 1) Your Answer:single-stranded (ss) RNA Correct Answer:All of the listed responses are correct. No. Single-stranded RNA is the genetic material of certain viruses, but there is a better answer.
- Viruses that infect bacteria are called _____. (Concept 19. 1) Your Answer:capsomeres Correct Answer:bacteriophages No. Capsomeres are the protein subunits of the capsid, the protein shell that encloses the viral genome.
- HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because _____. (Concept 19. 2) Your Answer:other cells produce toxins that destroy the virus before infection can take place Correct Answer:the virus binds to specific receptors that are only present on certain immune cells No. This is not true.
- Cancer cells often have protein receptor molecules on their surfaces that differ from those on normal body cells. Given this fact, how might viruses be used to treat cancer? (Concept 19. 2) Your Answer:Viruses could be engineered to infect only cancer cells by altering viral surface proteins to recognize only the receptors on cancer cells. Correct. The host specificity of viruses could be used to make cancer cells "sick" whereas normal body cells would not be infected. This approach would reduce the collateral damage seen in chemotherapy.
- Why are phages useful in treating bacterial infections in humans? (Concept 19. 2) Your Answer:Because of their host specificity, they only attack bacteria. They do not affect eukaryotic cells. Correct Answer:The first three answers are correct. No. This is true, but there is a better answer.
- Which of the following can a virus do without a host cell? (Concept 19. 2) Your Answer:transcribe DNA Correct Answer:None of the listed responses is correct. No. DNA viruses use the RNA polymerase of the host to transcribe viral DNA.
- When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm? (Concept 19. 2) Your Answer:the tail fibers Correct Answer:only the nucleic acid No. The tail remains outside the host cell.
- The phage reproductive cycle that kills the bacterial host cell is a _____ cycle, and a phage that always reproduces this way is a _____ phage. (Concept 19. 2) Your Answer:lysogenic ... virulent Correct Answer:lytic ... virulent No. A virus with a lysogenic cycle is a temperate virus.
- In the lytic life cycle of phages _____. (Concept 19. 2) Your Answer:the viral capsid is assembled according to the genetic information of the bacterium Correct Answer:the cell typically dies, releasing many copies of the virus No. The viral capsid assembles spontaneously from its subunits, the capsomeres.
- Restriction enzymes help defend bacteria against viral infections by _____. (Concept 19. 2) Your Answer:cutting viral DNA once it has entered the cell Correct. Restriction enzymes cut viral DNA, but bacterial DNA is modified in such a way as to protect it against the enzymes.
- A phage that inserts itself into the host DNA is called _____. (Concept 19. 2) Your Answer:a capsomere Correct Answer:lysogenic No. Capsomeres are the protein subunits of capsids.
- A prophage is a(n) _____. Concept 19. 2) Your Answer:virus that infects bacteria Correct Answer:viral genome that has been incorporated into a bacterial cell's chromosome No. This type of virus is called a bacteriophage.
- In the lysogenic cycle of phages _____. (Concept 19. 2) Your Answer:the viral nucleic acid inserts itself into the host chromosome Correct Answer:All of the listed responses are correct. No. This statement is true, but it is not the best response.
- What is the origin of the phospholipid membrane that envelops many animal viruses? (Concept 19. ) Your Answer:It is "stolen" from the host cell, but it contains some proteins encoded by the viral genome. Correct. Newly formed viruses "cloak" themselves in phospholipid membrane derived from the host, but certain components encoded by the viral genome are also included in the envelope.
- Why can flare-ups of herpesvirus infection recur throughout a person's life? (Concept 19. 2) Your Answer:Herpesvirus may cloak itself in a cell's nuclear envelope, making it very difficult for the immune system to recognize it. Correct Answer:Herpesvirus can leave its DNA behind as minichromosomes in nerve cell nuclei. Stress can trigger another round of virus production, producing characteristic blisters and sores. No. Herpesvirus does use the nuclear envelope's membrane as its envelope at some times, but recurrences are caused by the virus leaving its DNA in the nucleus of certain nerve cells. When triggered, the viral DNA can set off another round of virus production.
- How do retroviruses, such as HIV, differ from other viruses? (Concept 19. 2) Your Answer:They contain DNA that is used as a template to make RNA. Correct Answer:They can transcribe a DNA copy from a RNA template. No. Retroviruses are not DNA viruses.
- Reverse transcription, carried out by retroviruses, is the process by which _____. (Concept 19. 2) Your Answer:RNA information is "read" to form a protein molecule Correct Answer:RNA information is copied into DNA No. This is translation.
- Which statement below is a correct comparison of a "regular" RNA virus and an RNA retrovirus? (Concept 19. 2) Your Answer:Only the RNA retrovirus performs translation. Correct Answer:Both produce protein coats via translation of mRNA. No. Translation is required for the manufacture of viral proteins.
- When comparing DNA and RNA viruses, which mutate more quickly, and why? (Concept 19. 2) Your Answer:RNA viruses, because RNA is single-stranded and thus more prone to mutations Correct Answer:RNA viruses, because no proofreading is done on RNA molecules No. RNA viruses mutate more quickly because RNA molecules are not proofread.
- The symptoms of a viral infection in a person can be caused by _____. (Concept 19. 3) Your Answer:the reaction of the individual's immune system to the infection Correct Answer:All of the listed responses are correct. No. This statement is true, but there is a better response.
- Vaccines for viral diseases are _____ and help prevent infection by _____. (Concept 19. 3) Your Answer:protease inhibitors ... preventing synthesis of envelope proteins Correct Answer:harmless derivatives of pathogenic viruses ... stimulating the immune system to mount a defense against the actual pathogen No. Protease inhibitors are not vaccines but are instead a separate class of antiviral drugs.
- Emerging viruses can originate from which of the following sources? (Concept 19. 3) Your Answer:animal viruses Correct Answer:All of the listed responses are correct. No. This is a possible source, but there is a better answer.
- What is the function of hemagglutinin in the influenza virus? (Concept 19. 3) Your Answer:Hemagglutinin is involved in assembling the membrane envelope that the virus uses as a cloak when it leaves an infected cell. Correct Answer:Hemagglutinin is the protein that helps the influenza virus attach to host cells. No. Hemagglutinin helps the virus attach to host cells.
- Birds act as a natural _____ for the influenza _____ virus. Concept 19. 3) Your Answer:reservoir ... C Correct Answer:reservoir ... A No. Influenza type C only infects humans.
- Which of the following is an example of vertical transmission of a virus in plants? (Concept 19. 3) Your Answer:An infected plant produces seeds that contain the virus, giving rise to infected progeny. Correct. Vertical transmission refers to the spread of a virus from parent to offspring.
- Plant viruses spread throughout the plant by way of _____. (Concept 19. 3) Your Answer:the lymphatic system Correct Answer:plasmodesmata No. Plants do not have a lymphatic system.
- Circular RNA molecules that function like a virus in plants are termed _____. (Concept 19. 3) Your Answer:viroid Correct. Viroids are tiny molecules of circular RNA that infect plants.
- Prions are _____ that are thought to cause disease by _____. (Concept 19. 3) Your Answer:mutant DNA molecules ... encoding toxic proteins Correct Answer:abnormally shaped proteins ... inducing similar but normally shaped proteins in the brain to adopt the abnormal form No. Prions are proteins.
- A new pathogenic form of influenza A can emerge when _____. (Concept 19. 3) Your Answer:a virus with a novel genetic makeup recombines with viruses that circulate widely among humans Correct Answer:All of the listed factors likely contribute to the emergence of a new pathogenic strain of influenza A. No. This can contribute to the emergence of a new pathogenic strain of influenza A virus but there is a better answer.
- What is the prevailing hypothesis for the surprisingly low infection and mortality rate among people over 64 years of age during the 2009 H1N1 pandemic? Concept 19. 3) Your Answer:Older people were likely exposed to earlier H1N1 viruses that primed their immune systems for the virus of the 2009 pandemic. Correct. It is proposed that prior exposure to earlier H1N1 viruses primed the immune system of older people so that they were able to mount an immune response to the recent H1N1 virus.
- The avian flu virus H5N1 is considered a greater long-term threat than the swine flu virus H1N1 because _____. (Concept 19. 3) Correct Answer:it has a significantly higher mortality rate.
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