ch 19 pretest
new pathogenic form of influenza A can emerge when _____.
All of the listed factors likely contribute to the emergence of a new pathogenic strain of influenza A.
Which of the following, if any, may be a component of a virus?
All of the listed responses are correct. single-stranded (ss) RNA double-stranded (ds) DNA protein phospholipid bilayer
The symptoms of a viral infection in a person can be caused by _____.
All of the listed responses are correct. the reaction of the individual's immune system to the infection the production of toxins by infected cells the death of infected cells toxic viral components, such as envelope proteins
Emerging viruses can originate from which of the following sources?
All of the listed responses are correct. animal viruses the mutation of existing human viruses viruses previously confined to small, isolated populations that can now spread due to technological or social changes such as the development of affordable international travel
In the lysogenic cycle of phages _____. (see book section: Concept 19.2: Viruses replicate only in host cells) the nucleic acid core of the phage is all that enters the host cell only a small number of the viral genes are expressed the viral nucleic acid inserts itself into the host chromosome the viral nucleic acid is replicated along with the host DNA All of the listed responses are correct.
All of the listed responses are correct. the nucleic acid core of the phage is all that enters the host cell only a small number of the viral genes are expressed the viral nucleic acid inserts itself into the host chromosome the viral nucleic acid is replicated along with the host DNA
Which of the following is an example of vertical transmission of a virus in plants?
An infected plant produces seeds that contain the virus, giving rise to infected progeny.
Which statement below is a correct comparison of a "regular" RNA virus and an RNA retrovirus?
Both produce protein coats via translation of mRNA.
What is the function of hemagglutinin in the influenza virus?
Hemagglutinin is the protein that helps the influenza virus attach to host cells.
Why can flare-ups of herpesvirus infection recur throughout a person's life?
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.
What is the origin of the phospholipid membrane that envelops many animal viruses?
It is "stolen" from the host cell, but it contains some proteins encoded by the viral genome.
Which of the following can a virus do without a host cell?
None of the listed responses is correct.
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?
Older people were likely exposed to earlier H1N1 viruses that primed their immune systems for the virus of the 2009 pandemic.
Reverse transcription, carried out by retroviruses, is the process by which _____.
RNA information is copied into DNA
When comparing DNA and RNA viruses, which mutate more quickly, and why?
RNA viruses, because no proofreading is done on RNA molecules
Why are phages useful in treating bacterial infections in humans?
The first three answers are correct. Because of their host specificity, they only attack bacteria. They do not affect eukaryotic cells. Because of their specificity, a phage can be used that will only infect the pathogenic bacteria, leaving helpful bacteria alone. Because phages are free to evolve, bacteria are less likely to develop a lasting resistance to them.
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?
The viral envelope forms as the virus leaves the host cell.
How do retroviruses, such as HIV, differ from other viruses?
They can transcribe a DNA copy from a RNA template.
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?
Viruses could be engineered to infect only cancer cells by altering viral surface proteins to recognize only the receptors on cancer cells.
Prions are _____ that are thought to cause disease by _____.
abnormally shaped proteins ... inducing similar but normally shaped proteins in the brain to adopt the abnormal form
Viruses that infect bacteria are called _____.
bacteriophages
Restriction enzymes help defend bacteria against viral infections by _____.
cutting viral DNA once it has entered the cell
Vaccines for viral diseases are _____ and help prevent infection by _____.
harmless derivatives of pathogenic viruses ... stimulating the immune system to mount a defense against the actual pathogen
The avian flu virus H5N1 is considered a greater long-term threat than the swine flu virus H1N1 because _____.
it has a significantly higher mortality rate
A phage that inserts itself into the host DNA is called _____.
lysogenic
The phage reproductive cycle that kills the bacterial host cell is a _____ cycle, and a phage that always reproduces this way is a _____ phage.
lytic ... virulent
When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm?
only the nucleic acid
Plant viruses spread throughout the plant by way of _____.
plasmodesmata
Birds act as a natural _____ for the influenza _____ virus.
reservoir ... A
In the lytic life cycle of phages _____.
the cell typically dies, releasing many copies of the virus
Viruses can vary with respect to all of the following characteristics except _____.
the presence or absence of metabolic machinery
HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because _____.
the virus binds to specific receptors that are only present on certain immune cells
A prophage is a(n) _____. (see book section: Concept 19.2: Viruses replicate only in host cells) type of retrovirus emerging virus viral genome that has been incorporated into a bacterial cell's chromosome virus that infects bacteria prion that has been integrated into a bacterial cell's chromosome
viral genome that has been incorporated into a bacterial cell's chromosome
Circular RNA molecules that function like a virus in plants are termed _____.
viroid
