GRE Subject Test: Biology : Understanding Animal and Plant Viruses
Study concepts, example questions & explanations for GRE Subject Test: Biology
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Example Questions
Example Question #3 : Viruses
Which of the following statements describes a lysogenic infection?
The virus will inject its genome into the host cell through its tail
The virus enters the cell, hijacks host reproductive machinery, and creates new viruses that will destroy the cell
The virus incorporates its nucleic acid into the host's genome
A lysogenic infection can only be done by DNA viruses
The virus incorporates its nucleic acid into the host's genome
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.
Example Question #2 : Viruses
Which of the following is not a component of HIV?
Proteases
Ribosomes
Protein
Reverse transcriptase
RNA
Ribosomes
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.
Example Question #3 : Microbiology
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
V
IV
II
I
III
III
The question addresses the Baltimore classification system for viral genetic information. Viruses contain some form of DNA or RNA, but never both.
Example Question #4 : Microbiology
What molecule would you not expect to find in a retrovirus?
Uracil
Cytosine
Thymine
Guanine
Adenine
Thymine
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.
Example Question #6 : Viruses
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 has ribosomes; viruses do not have ribosomes
Neisseria is enveloped; no viruses are enveloped
Neisseria infects only one cell type; viruses have wide variety in their cellular targets
Neisseria does not have flagella; all viruses have flagella
Neisseria contains DNA; all viruses contain RNA
Neisseria has ribosomes; viruses do not have ribosomes
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.
Example Question #7 : Viruses
What component is common for all viruses?
A protein coat
A protective envelope
DNA
RNA
A protein coat
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.
Example Question #4 : Viruses
Which of the following best describes retroviral DNA that has been incorporated into a host genome?
Virion
Endogenous retrovirus
Provirus
Exogenous retrovirus
Retroelements
Provirus
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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