Microbiology Chapter 6 DSM
Which of the following suffixes would be used to describe a viral family? A) -virales B) -viridae C) -virus D) -virinae
B) -viridae The suffix -viridae is used to describe the family name of a virus. The suffix -virales refers to the order, -virus to the genus of a virus, and -virinae to a subfamily.
Cells can only contain which of the following types of genomes? A) A double-stranded DNA genome B) A single-stranded DNA genome C) A single-stranded RNA genome D) A double-stranded RNA genome
A) A double-stranded DNA genome Although cells have larger and more complex genomes than viruses, cells can only have double-stranded DNA genomes. In contrast, viruses can have either an RNA- or DNA-based genome (but usually not both), and the nucleic acid present can be either single or double-stranded. Single-stranded RNA viruses can also be positive-stranded (ssRNA+) or negative-stranded (ssRNA-) as well as divided into individual pieces, or "segmented."
Which of the following methods is used to cultivate bacteriophages in the laboratory setting? A) Bacteriophages are cultivated in bacteria in liquid broth or on solid medium. B) Bacteriophages are cultivated in tissue cultures. C) Bacteriophages are grown with the streak plate method. D) Bacteriophages are cultivated in embryonated eggs.
A) Bacteriophages are cultivated in bacteria in liquid broth or on solid medium. Bacteriophages infect bacterial cells, which allows for easy cultivation of these viruses in the lab. They are usually mixed with a particular host strain and then incubated in liquid broth culture or on solid agar in a petri plate. The advantage of the solid agar approach is that it allows for a technique called the plaque assay, which allows for quantification of bacteriophages in a sample. Most animal viruses are grown using tissue culture techniques. A variety of commercially available human and animal cell lines can be used to support viral replication. The streak plate method is used to isolate bacterial colonies. Embryonated eggs are useful for growing certain animal viruses. Active virions are injected into the egg, after which the egg is incubated to allow for viral replication. The resulting virions are purified from the eggs and used for a number of applications, including vaccines.
Which of the following is NOT a mechanism of an antiviral drug? A) Blocking viral ribosomes B) Blocking viral attachment C) Blocking viral penetration D) Blocking uncoating
A) Blocking viral ribosomes Any step in the viral replication pathway is a potential drug target, e.g. blocking viral attachment, viral penetration, or uncoating. As such, basic research into how a given virus gains entry into a host cell and then replicates it is essential to developing antiviral drugs. Studying how our own immune systems successfully end certain viral infections also gives us a model for developing antiviral treatments. Viruses lack ribosomes; therefore, ribosomes cannot serve as an antiviral drug target.
The protein shell that packages and protects the genome and also accounts for the bulk of a virion's mass is called a __________. A) Capsid B) Capsomere C) Tail Fiber D) Envelope
A) Capsid The protein shell that packages and protects the genome and also accounts for the bulk of a virion's mass is called a capsid. A capsid's shape is based on how the individual three-dimensional subunits, called capsomeres, are arranged. The capsids of most animal viruses have either helical or icosahedral symmetry, although there are exceptions. The tail fibers found on bacteriophages help the virus adhere to the specific protein on the bacterial cell wall surface. Some animal viruses have a lipid-based envelope that surrounds the capsid. Enveloped viruses develop by budding from the host, during which they acquire a portion of the cell membrane. The envelope is taken with them as a coating as they exit the cell.
Viruses do NOT infect which of the following organisms? A) Viruses can infect all forms of life. B) Bacteria C) Fungi D) Animals
A) Viruses can infect all forms of life. Viruses can infect all forms of life. Some viruses specifically infect prokaryotes, including bacteria and archaea. Other viruses specifically infect eukaryotes (plants, protists, animals, and fungi). The structural and genomic features of a virus dictate the specific type of host cell that the virus can infect as well as the progression of the infection.
Nucleic acid detection techniques: A) can detect new viruses and early-stage infections that antibody-antigen tests are likely to miss. B) are less sensitive than the antigen-antibody-based tests. C) are much slower than the antigen-antibody-based tests. D) are used to culture animal viruses in the lab.
A) can detect new viruses and early-stage infections that antibody-antigen tests are likely to miss. Nucleic acid detection techniques can detect new viruses and early-stage infections that antibody-antigen tests are likely to miss. They are more sensitive and sometimes more rapid than antigen-antibody-based tests. To perform the test, DNA and RNA are extracted from a clinical sample such as sputum, blood, cerebrospinal fluid, or tissue. Then very specific segments of viral nucleic acid, usually those coding for a unique viral gene, can be detected by using fluorescence-labeled probes or by sequencing the nucleic acids.
Which of the following statements are incorrect about the transmission of Creutzfeldt-Jakob disease? A) In the past, cases of CJD were transmitted through treatment with human growth hormone harvested from cadaver pituitary tissue. B) Creutzfeldt-Jakob disease is never inherited. C) CJD can be acquired through a dura mater graft used to treat traumatic head injury. D) Creutzfeldt-Jakob disease can be transmitted through respiratory droplets. E) Iatrogenic transmission can occur through contaminated surgical instruments.
B) Creutzfeldt-Jakob disease is never inherited and D) Creutzfeldt-Jakob disease can be transmitted through respiratory droplets. Spongiform encephalopathies can be inherited or acquired. Creutzfeldt-Jakob disease (CJD) is a spongiform encephalopathy that occurs in humans. CJD can be inherited, accounting for about 15 percent of human prion disease cases. Variant CJD can occur through consumption of beef contaminated with the prion. Sporadic CJD can occur spontaneously through a mutation in the normal cellular prion protein, affecting 200 to 400 people annually in the United States. CJD can occur through iatrogenic transmission, which is accidental transmission to a patient as a result of a medical intervention. Iatrogenic CJD has been traced back to contaminated surgical instruments as well as through tissue transplants derived from infected cadavers. Historically, human growth hormone was harvested from the pituitary glands of cadavers. Cases of CJD were transmitted through treatment with this hormone before 1985, when the hormone started being produced in genetically engineered cells in a lab, eliminating the risk of iatrogenic CJD. Prion diseases, including CJD, are not transmitted through respiratory droplets.
Which of the following oncogenic viruses may integrate into the host genome? A) Hepatitis C virus B) Human T-lymphotropic viruses (HTLVs) C) Epstein-Barr virus D) Hepatitis B virus E) Human papilloma viruses (HPVs) F) Human herpes virus-8 (HHV-8)
B) Human T-lymphotropic viruses (HTLVs) and E) Human papilloma viruses (HPVs) Viruses that cause persistent infections are often associated with cancer. Those that can cause cancer are called oncogenic viruses. Some of them, such as human papilloma viruses (HPVs) and human T-lymphotropic viruses (HTLVs), integrate into the host genome. There are over 200 different types of HPVs, at least 40 of which spread through sexual contact. The vast majority cause benign warts. About a dozen HPV types have been linked to cancer. The human T-lymphotropic viruses HTLV-1 and HTLV-2 are also clinically important; these retroviruses form a provirus and can quietly persist in host cells for more than a decade before emerging to cause leukemia or lymphoma. The primary modes of transmission are through breast milk, sexual contact, and blood contact. Epstein-Barr virus, human herpes virus-8, hepatitis B virus, and hepatitis C virus are maintained episomally and do not integrate into the genome.
Which of the following would be the best general description of a "virus"? A) Viruses are cells without a nucleus or other membrane-bound organelles. B) Viruses are acellular infectious agents. C) Viruses are cells with a nucleus and membrane-bound organelles. D) Viruses are acellular infectious agents with DNA genomes.
B) Viruses are acellular infectious agents. Unlike prokaryotes and eukaryotes, viruses are not made of cells, which is why they are described as "acellular". One reason viruses are considered nonliving is that viruses are incapable of synthesizing their own components, such as nucleic acids or proteins, without the help of the host cells they infect. This means they are "obligate intracellular pathogens," in that they cannot cause disease without first infecting a host cell. Because they are acellular, they lack membrane-bound organelles and other cellular structures. They are also variable in that their genome is not always double-stranded DNA. Some viruses contain single-stranded DNA genomes, and others contain single or double-stranded RNA genomes.
Which of the following viral genomes is immediately ready for translation after the virus gains entry into the cell? A) dsDNA B) ssRNA+ C) dsRNA D) ssDNA
B) ssRNA+ Some single-stranded RNA genomes are in a form that can be directly translated by host cell ribosomes in the cytoplasm. These are single-stranded, positive, or sense-stranded RNA (ssRNA+) viruses. Some examples include poliovirus, rubella virus, and dengue fever virus. If the infecting virus is a double-stranded DNA virus (dsDNA), such as human parvovirus, the viral DNA is transcribed using host cell RNA polymerases, and the resulting mRNA is then translated into protein. If the virus has a double-stranded RNA (dsRNA) genome, the RNA has to be unwound before RNA polymerases can transcribe it into an mRNA format. The process resembles that of a double-stranded DNA virus, but instead of using host cell RNA polymerases, virally encoded RNA-dependent RNA polymerases are required. Rotaviruses, which cause severe diarrhea, are an example of dsRNA viruses. If the virus is a single-stranded DNA virus (ssDNA), then it is converted to a double-stranded form before transcription is performed.
In a(n) __________ infection, viral replication peaks, followed by immune clearance of the virus. A) Latent B) Persistent C) Acute D) Chronic
C) Acute In an acute infection, viral replication peaks, followed by immune clearance of the virus. Acute infections run their course and are cleared by the host immune system. The common cold and influenza are examples of acute viral infections. Persistent viruses tend to remain in the host for long periods, from many weeks to a lifetime. Most persistent infections can be described as chronic or latent. Chronic infections are characterized by continuous release of virions over time and a slow progression of disease. Latent infections are distinguished by flare-ups with intermittent periods of dormancy (latency). During a flare-up, virions are shed and the infected person experiences symptoms. When a flare-up concludes, the virus retreats into a period of inactivity, during which virion levels fall drastically and may be difficult to detect.
Which of the following is a major difference between bacteriophages and animal viruses? A) Animal viruses are assembled in the cytoplasm of cells; bacteriophages are assembled in the nucleus of a bacterial cell. B) Animal viruses are only released from the host cell by cellular lysis; bacteriophages are released by budding. C) Animal viruses enter the host cell; bacteriophages inject their genome into the host without entering. D) There are no differences between animal viruses and bacteriophages.
C) Animal viruses enter the host cell; bacteriophages inject their genome into the host without entering. Among various differences between animal viruses and bacteriophages, one major difference between them is that animal viruses enter the host cell; bacteriophages inject their genome into the host without entering. Animal viruses enter the host cell by endocytosis of the entire virus or through fusion of the viral envelope with the cellular membrane. Both animal viruses and bacteriophages are assembled in the cytoplasm of cells. In addition, bacterial cells do not have nuclei. Animal viruses are released from the cell by budding or by cellular lysis, depending on the virus; bacteriophages are released by lysis of the bacterial cell.
Bacteriophages use different mechanisms for host cell infection and viral replication. During the lytic replication pathway, bacteriophages infect the host bacterial cells and immediately build new virions. During which of the key steps is the genome packed into the capsid and phage structures put together? A) Replication B) Penetration C) Assembly D) Release
C) Assembly During assembly, once all the parts of the bacteriophage are replicated, viral factors pack the viral genome into the capsid, and the remaining phage parts are assembled. During penetration, the bacteriophage injects genetic material into the cell through the host's cell wall and plasma membrane. The empty capsid remains outside the cell. During replication (synthesis), once the viral genome is inside, the bacteriophage commandeers host cell factors to transcribe and translate viral genes. Bacteriophages encode an enzyme called lysozyme, which breaks down host cell walls and causes bacterial cell lysis (bursting) once the newly assembled phages are mature. The released bacteriophages can then infect other cells.
Which of the following statements INCORRECTLY describes viral spikes? A) Spikes have an important role in determining what species and tissues the virus can infect. B) Spikes are glycoprotein extensions that help viruses attach and gain entry to host cells. C) Lipid-based spikes make up the envelope that surrounds the capsid. D) Spikes may be recognized by the host immune system that mounts an immune response to them.
C) Lipid-based spikes make up the envelope that surround the capsid. Spikes (also called peplomers) protrude from the viral capsid or, if present, from the viral envelope and are made up of glycoproteins. These glycoprotein extensions help viruses attach and gain entry to host cells. Because they only bind to specific factors on a given host cell, spikes have an important role in determining what species and tissues the virus can infect, similar to how a lock and key must match. The host immune system may also recognize spikes and mount an immune response to them.
The most common drugs that block replication are __________. A) Nucleoside reverse transcriptase inhibitiors (NRTIs) B) Interferons C) Nucleoside analogs D) Protease inhibitors
C) Nucleoside analogs The most common drugs that block replication are nuceloside analogs. Nucleoside analogs are activated in virally infected cells into compounds that mimic normal nucleotides. These analogs are chemically different from natural nucleotides and represent a chemical "dead end" for nucleic acid replication. When used by DNA or RNA polymerase in place of a natural nucleotide, nucleic acid replication is interrupted. Nucleoside reverse transcriptase inhibitors (NRTIs) target reverse transcriptase enzymes. Reverse transcriptase is required by retroviruses to convert their RNA genome into a DNA format, after which the virus integrates into the host genome and perpetuates viral replication. Interferons are released by virally infected cells, causing neighboring, uninfected cells to make defensive changes that limit viral entry and/or replication. Interferons can be artificially produced and used to treat certain viral infections. Protease inhibitors prevent the assembly of maturation of infectious virions. Protease inhibitors are used to target HIV proteases to limit viral assembly.
Which of the following acellular agents do NOT have any genetic material and therefore do NOT replicate? A) Bacteria B) Archaea C) Prions D) Protists
C) Prions Bacteria, archaea, and protists are cells. All cells have three structure features in common; they contain a DNA genome, ribosomes, and a plasma membrane. Viable cells will also actively replicate if conditions are favorable. Prions are acellular agents that do not have any genetic material and therefore do not replicate. Prions cause protein misfolding and clumping that lead to brain tissue degeneration. As the brain tissue deteriorates, spongy holes are left in the brain, hence the name "spongiform" encephalopathy.
Which of the following terms is used to describe the shape of a virus? A) Coccus B) Bacillus C) Spirillum D) Icosahedral
D) Icosahedral Coccus, bacillus, and spirillum are terms used to describe bacterial morphologies. Capsids of some animal viruses have icosahedral symmetry. Icosahedral capsids look like three-dimensional polygons but may appear fairly spherical—just as a soccer ball is spherical yet made of multiple hexagon and pentagon shapes.
Why are you supposed to get a new flu shot every year? A) Influenza viruses may undergo a major genetic reassortment that dramatically changes HA and NA spikes, called antigenic shift. B) The vaccine composition is not altered from year to year. C) The RNA genome of influenza mutates frequently, causing minor changes. This is referred to as antigenic drift. D) The flu vaccine confers lifelong immunity.
C) The RNA genome of influenza mutates frequently, causing minor changes. This is referred to as antigenic drift. The influenza vaccine does not confer lifelong immunity. The influenza RNA genome mutates more and evolves faster than its DNA counterparts, creating the need for the composition of the vaccine to be changed every season. This frequent occurrence of minor changes in the genome is also referred to as antigenic drift. These changes allow the virus to evade the antibody response by making the new strains different enough to go unrecognized by the immune system. In contrast, influenza viruses may undergo a major genetic reassortment that dramatically changes HA and NA spikes, termed antigenic shift, which can lead to viral strains with increased infectivity or expanded host range. Antigenic shift occurs when two different virions infect a single host cell, leading to a new strain of influenza virus. The drastic change in the virus usually means that people have no residual immune protection from prior influenza infections or vaccinations.
Which of the following statements are true about SARS-CoV-2? A) SARS-CoV-2 has an antisense RNA genome. B) The virus attaches to host cells via its neuraminidase spike. C) The genome of SARS-CoV-2 undergoes mutations. D) The strain designation of SARS-CoV-2 is H1N1. E) SARS-CoV-2 is a naked virus. F) SARS-CoV-2 causes Covid-19.
C) The genome of SARS-CoV-2 undergoes mutations and F) SARS-CoV-2 causes Covid-19. SARS-CoV-2 is the causative agent of the disease Covid-19. This virus is a single-stranded sense RNA virus that undergoes frequent mutations, leading to the development of new viral strains and prolonging the Covid-19 pandemic. Neuraminidase is a spike found on influenza viruses that is involved in viral replication. Influenza strains are named based on the spikes present on their envelope; for example, the strain that caused the Spanish flu pandemic was H1N1.
Which of the following steps is found in the lysogenic replication pathway but NOT in the lytic replication pathway? A) Assembly B) Penetration C) Attachment D) Integration
D) Integration Some bacteriophages, such as lambda phages, are called temperate phages. These bacteriophages can use either a lytic or a lysogenic pathway. The lytic pathway kills the host cell when newly made bacteriophages are released. During the lysogenic pathway, following penetration, the phage genome is integrated into the host cell genome, forming a prophage. This step is unique to the lysogenic pathway. As the infected bacterial cell divides, it copies its own genome as well as the prophage's genome. Therefore, a single infection event ultimately results in many cells carrying the bacteriophage's genome. If a host cell carrying a prophage is stressed, the prophage may excise itself from the host genome and enter the lytic replication pathway. Attachment, penetration, and assembly are steps found in both the lytic and lysogenic cycles.
Which type of method is used to determine if a prior exposure to a virus occurred? A) Tissue culture B) Plaque assay C) Gram staining D) Latex agglutination test
D) Latex agglutination test Testing for an antibody response to a specific antigen serves as evidence of a prior infection. The latex agglutination test is one commonly performed test to collect this evidence. To perform this test, latex beads are coated with viral proteins. If the patient has antibodies to the viral proteins coating the beads, then the beads will agglutinate when exposed to the patient's serum (the part of blood that contains antibodies). Plaque assays are used to determine the number of bacteriophages in a sample. When lytic bacteriophages lyse out of the host cell, they kill the host cell, leaving behind a clear zone called a plaque on the growing plate of bacteria. The Gram staining technique is based on the differences in the cell wall of certain bacteria, allowing their characterization as either Gram-negatives or Gram-positives. Tissue culture involves cultivating viruses by growing them in either human, plant, or animal cells.
Which of the following is NOT a property used to group viruses? A) Presence or absence of an envelope B) Type of nucleic acid present (DNA or RNA) C) Capsid symmetry (helical, icosahedral, or complex) D) Unicellularity versus multicellularity
D) Unicellularity versus multicellularity Viruses are acellular infectious agents that are not considered "alive," and we cannot use the term cell to describe them. Therefore, other properties are used to group them, e.g. by the type of nucleic acid present (DNA or RNA), capsid symmetry (helical, icosahedral, or complex), presence or absence of an envelope, and genome architecture (e.g. ssDNA or ssRNA).