Divisions of Life and Viruses - GRE
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Which of the following is not a component of HIV?
Which of the following is not a component of HIV?
HIV is a retrovirus, meaning that it contains RNA as its genetic material, and thus reverse transcriptase to code for DNA from the RNA template. It also has a protein coat, and must use proteases in order to degrade the host cell membrane to inject its RNA. It does not, however, have ribosomes. It will eventually use the host ribosomes to translate its own genetic material.
HIV is a retrovirus, meaning that it contains RNA as its genetic material, and thus reverse transcriptase to code for DNA from the RNA template. It also has a protein coat, and must use proteases in order to degrade the host cell membrane to inject its RNA. It does not, however, have ribosomes. It will eventually use the host ribosomes to translate its own genetic material.
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Which of the following is not a described type of virus?
I. A virus containing double strand DNA
II. A virus containing single strand DNA
III. A virus containing single strand RNA and single strand DNA
IV. A virus containing single strand RNA
V. A virus containing double strand RNA
Which of the following is not a described type of virus?
I. A virus containing double strand DNA
II. A virus containing single strand DNA
III. A virus containing single strand RNA and single strand DNA
IV. A virus containing single strand RNA
V. A virus containing double strand RNA
The question addresses the Baltimore classification system for viral genetic information. Viruses contain some form of DNA or RNA, but never both.
The question addresses the Baltimore classification system for viral genetic information. Viruses contain some form of DNA or RNA, but never both.
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What molecule would you not expect to find in a retrovirus?
What molecule would you not expect to find in a retrovirus?
Retroviruses carry RNA and when they infect a host cell, they use their own reverse transciptase to made DNA from that RNA; therefore, within the virus, there are only the molecules that make up RNA. Uracil is used in RNA place of thymine, which can be found in DNA. Cytosine, guanine, and adenine can be found in both DNA and RNA.
Retroviruses carry RNA and when they infect a host cell, they use their own reverse transciptase to made DNA from that RNA; therefore, within the virus, there are only the molecules that make up RNA. Uracil is used in RNA place of thymine, which can be found in DNA. Cytosine, guanine, and adenine can be found in both DNA and RNA.
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Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.
The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.
Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.
Which of the following is true of Neisseria, but not true of a virus?
Sexually transmitted diseases are a common problem among young people in the United States. One of the more common diseases is caused by the bacterium Neisseria gonorrhoeae, which leads to inflammation and purulent discharge in the male and female reproductive tracts.
The bacterium has a number of systems to evade host defenses. Upon infection, it uses pili to adhere to host epithelium. The bacterium also uses an enzyme, gonococcal sialyltransferase, to transfer a sialyic acid residue to a gonococcal surface lipooligosaccharide (LOS). A depiction of this can be seen in Figure 1. The sialyic acid residue mimics the protective capsule found on other bacterial species.
Once infection is established, Neisseria preferentially infects columnar epithelial cells in the female reproductive tract, and leads to a loss of cilia on these cells. Damage to the reproductive tract can result in pelvic inflammatory disease, which can complicate pregnancies later in the life of the woman.
Which of the following is true of Neisseria, but not true of a virus?
Neisseria synthesizes proteins as a free living prokaryote. Viruses are generally dependent on host cellular machinery, and synthesize their proteins upon hijacking of a host ribosome.
Neisseria synthesizes proteins as a free living prokaryote. Viruses are generally dependent on host cellular machinery, and synthesize their proteins upon hijacking of a host ribosome.
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What component is common for all viruses?
What component is common for all viruses?
All viruses contain a protein coat (or capsule) that protects the genetic material (which can be either DNA or RNA). In some instances (such as herpes simplex), the virus can also contain an lipid envelope that serves as a membrane.
All viruses contain a protein coat (or capsule) that protects the genetic material (which can be either DNA or RNA). In some instances (such as herpes simplex), the virus can also contain an lipid envelope that serves as a membrane.
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Which of the following statements describes a lysogenic infection?
Which of the following statements describes a lysogenic infection?
A lysogenic infection involves the virus entering the cell and incorporating its nucleic acid into the host genome. RNA viruses are capable of this type of infection, but must first have their RNA be converted to DNA using the enzyme reverse transcriptase. The DNA genome remains dormant in the cell as it undergoes cellular divisions, increasing the number of cells that contain the viral DNA. This stage is known as the latent period.
Eventually, the viral genome will be stimulated and enter into the lytic viral cycle. During this phase, the virus hijacks the cell ribosomes and produces large quantities of the viral genome and proteins. Eventually the virus causes the cell to lyse, releasing more virions into the host.
A lysogenic infection involves the virus entering the cell and incorporating its nucleic acid into the host genome. RNA viruses are capable of this type of infection, but must first have their RNA be converted to DNA using the enzyme reverse transcriptase. The DNA genome remains dormant in the cell as it undergoes cellular divisions, increasing the number of cells that contain the viral DNA. This stage is known as the latent period.
Eventually, the viral genome will be stimulated and enter into the lytic viral cycle. During this phase, the virus hijacks the cell ribosomes and produces large quantities of the viral genome and proteins. Eventually the virus causes the cell to lyse, releasing more virions into the host.
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Which of the following best describes retroviral DNA that has been incorporated into a host genome?
Which of the following best describes retroviral DNA that has been incorporated into a host genome?
The correct answer is provirus. A retrovirus uses its own reverse transcriptase to synthesize DNA from its RNA. This DNA is then incorporated into the host genome via the integrase enzyme. The viral DNA in the host genome is referred to as a provirus; the host cell transcribes and translates the provirus to produce new copies of the virus, along with its own genome.
The correct answer is provirus. A retrovirus uses its own reverse transcriptase to synthesize DNA from its RNA. This DNA is then incorporated into the host genome via the integrase enzyme. The viral DNA in the host genome is referred to as a provirus; the host cell transcribes and translates the provirus to produce new copies of the virus, along with its own genome.
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Which of the following is the best description of a bacteriophage?
Which of the following is the best description of a bacteriophage?
A bacteriophage is a virus that infects bacteria. They are not considered living (becuase they cannot replicate on their own) organisms, nor are they techincally considered non-living organisms. They are called obligate intracellular organisms, because they are parasites (kill the cell) that require a host in order to replicate.
A bacteriophage is a virus that infects bacteria. They are not considered living (becuase they cannot replicate on their own) organisms, nor are they techincally considered non-living organisms. They are called obligate intracellular organisms, because they are parasites (kill the cell) that require a host in order to replicate.
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A lytic bacteriophage produces "substance X," which causes a host cell to lyse. At which point would the gene for substance X most likely be expressed?
A lytic bacteriophage produces "substance X," which causes a host cell to lyse. At which point would the gene for substance X most likely be expressed?
Substance X would logically be released in the later part of viral infection. This would be referred to as a "late gene." The reason is that the virus needs time to replicate and assemble its progeny in the host. Lysing the cell immediately after infection would be futile since no progeny could be created. Lytic viruses use the lysis event to escape from the cell, so it cannot occur after viral release. Finally, lytic viruses typically do not integrate into the host chromosome, lysogenic viruses do.
Substance X would logically be released in the later part of viral infection. This would be referred to as a "late gene." The reason is that the virus needs time to replicate and assemble its progeny in the host. Lysing the cell immediately after infection would be futile since no progeny could be created. Lytic viruses use the lysis event to escape from the cell, so it cannot occur after viral release. Finally, lytic viruses typically do not integrate into the host chromosome, lysogenic viruses do.
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What allows bacteriophages to only infect bacteria cells?
What allows bacteriophages to only infect bacteria cells?
The cell surface receptors that a virus recognizes and binds provides specificity for the organism(s) that it infects. Both lipopolysaccharides and teichoic acids are cell surface proteins of bacteria. Bacteriophages have very diverse mosaic genomes and replicate through both the lytic and lysogenic cycles. Retroviruses are RNA-positive strand viruses, which uses reverse transcriptase to synthesize DNA from an RNA template. Its DNA form of its genome is integrated into the host cell's genome.
The cell surface receptors that a virus recognizes and binds provides specificity for the organism(s) that it infects. Both lipopolysaccharides and teichoic acids are cell surface proteins of bacteria. Bacteriophages have very diverse mosaic genomes and replicate through both the lytic and lysogenic cycles. Retroviruses are RNA-positive strand viruses, which uses reverse transcriptase to synthesize DNA from an RNA template. Its DNA form of its genome is integrated into the host cell's genome.
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A mad scientist is working with a rare retrovirus under the hood, when he accidentally spills the viral sample over three live tissue cultures. Assuming the cultures were composed of stem cells, epithelial cells, and muscle cells, in which sample would the mad scientist expect to find the lowest viral titer?
A mad scientist is working with a rare retrovirus under the hood, when he accidentally spills the viral sample over three live tissue cultures. Assuming the cultures were composed of stem cells, epithelial cells, and muscle cells, in which sample would the mad scientist expect to find the lowest viral titer?
This question requires knowledge of two concepts: first, that retroviruses integrate their own genetic material into the host and are propagated during normal cell division; second, that some cell types do not continue to divide once they have reached maturity (muscle and nerve).
This question requires knowledge of two concepts: first, that retroviruses integrate their own genetic material into the host and are propagated during normal cell division; second, that some cell types do not continue to divide once they have reached maturity (muscle and nerve).
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Prions are the suspected cause of a wide variety of neurodegenerative diseases in mammals. According to prevailing theory, prions are infectious particles made only of protein and found in high concentrations in the brains of infected animals. All mammals produce normal prion protein, PrPC, a transmembrane protein whose function remains unclear.
Infectious prions, PrPRes, induce conformational changes in the existing PrPC proteins according to the following reaction:
PrPC + PrPRes → PrPRes + PrPRes
The PrPRes is then suspected to accumulate in the nervous tissue of infected patients and cause disease. This model of transmission generates replicated proteins, but does so bypassing the standard model of the central dogma of molecular biology. Transcription and translation apparently do not play a role in this replication process.
This theory is a major departure from previously established biological dogma. A scientist decides to test the protein-only theory of prion propagation. He establishes his experiment as follows:
Homogenized brain matter of infected rabbits is injected into the brains of healthy rabbits, as per the following table:
Rabbit 1 and 2: injected with normal saline on days 1 and 2
The above trials serve as controls.
Rabbit 3 and 4: injected with homogenized brain matter on days 1 and 2
The above trials use unmodified brain matter.
Rabbit 5 and 6: injected with irradiated homogenized brain matter on days 1 and 2
The above trials use brain matter that has been irradiated to destroy nucleic acids in the homogenate.
Rabbit 7 and 8: injected with protein-free centrifuged homogenized brain matter on days 1 and 2
The above trials use brain matter that has been centrifuged to generate a protein-free homogenate and a protein-rich homogenate based on molecular weight.
Rabbit 9 and 10: injected with boiled homogenized brain matter on days 1 and 2
The above trials use brain matter that have been boiled to destroy any bacterial contaminants in the homogenate.
Some scientists argue that there must be a virus or bacterium that cause infectious diseases, and claim that there is likely a heretofore undiscovered microbe causing neurodegeneration that most scientists claim are caused by PrPRes. What is a key way for these scientists to distinguish viruses from bacteria?
Prions are the suspected cause of a wide variety of neurodegenerative diseases in mammals. According to prevailing theory, prions are infectious particles made only of protein and found in high concentrations in the brains of infected animals. All mammals produce normal prion protein, PrPC, a transmembrane protein whose function remains unclear.
Infectious prions, PrPRes, induce conformational changes in the existing PrPC proteins according to the following reaction:
PrPC + PrPRes → PrPRes + PrPRes
The PrPRes is then suspected to accumulate in the nervous tissue of infected patients and cause disease. This model of transmission generates replicated proteins, but does so bypassing the standard model of the central dogma of molecular biology. Transcription and translation apparently do not play a role in this replication process.
This theory is a major departure from previously established biological dogma. A scientist decides to test the protein-only theory of prion propagation. He establishes his experiment as follows:
Homogenized brain matter of infected rabbits is injected into the brains of healthy rabbits, as per the following table:
Rabbit 1 and 2: injected with normal saline on days 1 and 2
The above trials serve as controls.
Rabbit 3 and 4: injected with homogenized brain matter on days 1 and 2
The above trials use unmodified brain matter.
Rabbit 5 and 6: injected with irradiated homogenized brain matter on days 1 and 2
The above trials use brain matter that has been irradiated to destroy nucleic acids in the homogenate.
Rabbit 7 and 8: injected with protein-free centrifuged homogenized brain matter on days 1 and 2
The above trials use brain matter that has been centrifuged to generate a protein-free homogenate and a protein-rich homogenate based on molecular weight.
Rabbit 9 and 10: injected with boiled homogenized brain matter on days 1 and 2
The above trials use brain matter that have been boiled to destroy any bacterial contaminants in the homogenate.
Some scientists argue that there must be a virus or bacterium that cause infectious diseases, and claim that there is likely a heretofore undiscovered microbe causing neurodegeneration that most scientists claim are caused by PrPRes. What is a key way for these scientists to distinguish viruses from bacteria?
Bacteria have ribosomes to facilitate protein synthesis, but lack other membrane bound organelles such as nuclei, Golgi, or mitochondrion. Viruses lack all of these, including ribosomes.
Bacteria have ribosomes to facilitate protein synthesis, but lack other membrane bound organelles such as nuclei, Golgi, or mitochondrion. Viruses lack all of these, including ribosomes.
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Which of the following structures will never be found in a virus?
Which of the following structures will never be found in a virus?
A virus will either contain RNA or DNA; never both. These nucleic acids are essential for carrying and transmitting the viral genome. Some viruses can also have a lipid-rich envelope surrounding them.
Since viruses hijack cellular ribosomes in order to create their needed proteins, there will never be a virus containing ribosomes.
A virus will either contain RNA or DNA; never both. These nucleic acids are essential for carrying and transmitting the viral genome. Some viruses can also have a lipid-rich envelope surrounding them.
Since viruses hijack cellular ribosomes in order to create their needed proteins, there will never be a virus containing ribosomes.
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Which of the following is not true of retroviruses?
Which of the following is not true of retroviruses?
Retroviruses do not harbor their own DNA polymerase. Once inside a host cell, the viral reverse transcriptase reverse transcribes its ssRNA to DNA. At this point, integrase incorporates its synthesized DNA into the host genome. Expression of this viral DNA utilizes host cellular machinery.
Retroviruses do not harbor their own DNA polymerase. Once inside a host cell, the viral reverse transcriptase reverse transcribes its ssRNA to DNA. At this point, integrase incorporates its synthesized DNA into the host genome. Expression of this viral DNA utilizes host cellular machinery.
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Which of the following is not part of the lysogenic cycle?
Which of the following is not part of the lysogenic cycle?
The lytic cycle is a nondestructive viral cycle in which viral genetic code integrates into the host chromosome but allows the host to live normally. The virus does not take over cell machinery (in order to churn out new viral parts) until it enters the destructive lytic cycle. All other answer choices are indeed parts of the lysogenic cycle.
The lytic cycle is a nondestructive viral cycle in which viral genetic code integrates into the host chromosome but allows the host to live normally. The virus does not take over cell machinery (in order to churn out new viral parts) until it enters the destructive lytic cycle. All other answer choices are indeed parts of the lysogenic cycle.
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Which of these choices is not a characteristic present in archaea?
Which of these choices is not a characteristic present in archaea?
Only bacterial have peptidoglycan cell walls. The other traits are typical of at least some known archaea. The s-layer involves crystalline arrays of proteinaceous subunits, which are common to some archaea and bacteria.
Only bacterial have peptidoglycan cell walls. The other traits are typical of at least some known archaea. The s-layer involves crystalline arrays of proteinaceous subunits, which are common to some archaea and bacteria.
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What comprises the cell wall of archaea?
What comprises the cell wall of archaea?
The correct answer is pseudopeptidoglycan. This is molecularly different than peptidoglycan, which comprises the bacterial cell wall. However, both pseudopeptidoglycan and peptidoglycan cell walls are similar in function, shape and structure. Cellulose comprises the cell walls of plants, chitin comprises the cell walls of fungi and glycogen is the animal form of stored glucose, and is found in the liver and skeletal muscle.
The correct answer is pseudopeptidoglycan. This is molecularly different than peptidoglycan, which comprises the bacterial cell wall. However, both pseudopeptidoglycan and peptidoglycan cell walls are similar in function, shape and structure. Cellulose comprises the cell walls of plants, chitin comprises the cell walls of fungi and glycogen is the animal form of stored glucose, and is found in the liver and skeletal muscle.
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What is the difference between gram-negative and gram-positive bacteria?
What is the difference between gram-negative and gram-positive bacteria?
The main reaction that happens during a gram stain is the detection of the presence of peptidoglycan. Most bacterial cell walls contain peptidoglycan, but in varying amounts. If the cell contains large amounts of peptidoglycan, it will retain the crystal violet dye and display a purple coloration (this is gram-positive). If the cell does not contain a large quantity of peptidoglycan, it will display the counterstain and appear pink (this is gram-negative).
The gram-stain does not dictate whether or not a species belongs to the domain archaea. Archaea cell walls do not contain peptidoglycan and will not react to the stain. Note that archaea and bacteria are different domains altogether, though they share some similar characteristics.
The main reaction that happens during a gram stain is the detection of the presence of peptidoglycan. Most bacterial cell walls contain peptidoglycan, but in varying amounts. If the cell contains large amounts of peptidoglycan, it will retain the crystal violet dye and display a purple coloration (this is gram-positive). If the cell does not contain a large quantity of peptidoglycan, it will display the counterstain and appear pink (this is gram-negative).
The gram-stain does not dictate whether or not a species belongs to the domain archaea. Archaea cell walls do not contain peptidoglycan and will not react to the stain. Note that archaea and bacteria are different domains altogether, though they share some similar characteristics.
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Which type of bacteria is referred to as "rod-shaped?"
Which type of bacteria is referred to as "rod-shaped?"
There are three principal forms of bacteria. Spherical bacteria are termed cocci. Rod-shaped bacteria are called bacilli. Spiral bacteria are rigid (spirilla), flexible (spirochetes), or curved (vibrios).
There are three principal forms of bacteria. Spherical bacteria are termed cocci. Rod-shaped bacteria are called bacilli. Spiral bacteria are rigid (spirilla), flexible (spirochetes), or curved (vibrios).
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When seen under the microscope using a gram stain, the bacteria that causes strept throat whould have which of the following appearances?
When seen under the microscope using a gram stain, the bacteria that causes strept throat whould have which of the following appearances?
Streptococcus, the causative agent of strep throat, is a genus of gram-postitive (purple staining) cocci (spheres), in which the cells tend to form chains. Bacteria are described by a combination of their response to gram stain and their appearance. For example, "gram-positive streptococcus" indicate chains of spheres that stain purple.
Streptococcus, the causative agent of strep throat, is a genus of gram-postitive (purple staining) cocci (spheres), in which the cells tend to form chains. Bacteria are described by a combination of their response to gram stain and their appearance. For example, "gram-positive streptococcus" indicate chains of spheres that stain purple.
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