Viruses
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MCAT Biology › Viruses
Which of the following is not found in a virus?
Ribosomes
DNA
RNA
Proteins
Explanation
Viruses use the hosts ribosomes to translate their genes, and do not possess their own organelles for replication. Viruses are made of a protein buffy coat with genetic material (DNA or RNA) inside.
What component is common for all viruses?
A protein coat
DNA
RNA
A protective envelope
Explanation
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.
Which of the following is not a property of viruses?
Viruses cannot survive without a host
Viruses contain genetic information and have a capsid protein coat
Viruses are intracellular parasites
Some viruses can specifically target bacteria
Viruses can make copies of themselves using the host's machinery
Explanation
Viruses cannot reproduce and make copies of themselves without a host; however, they can survive on their own. Viruses can remain dormant in a non-biological environment before being transferred to a biological host.
All viruses carry some form of genetic material, either in the form of DNA or RNA, and have a protein coat to contain the genetic material. Bacteriophages are viruses that specifically target bacteria. By hijacking the cellular machinery of host cells, viruses are able to replicate, essentially becoming intracellular parasites.
Which of the following is the best description of a bacteriophage?
An obligate intracellular parasite
A living organism
A non-living organism
A prokaryote
A fungus
Explanation
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.
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
III
I
II
IV
V
Explanation
The question addresses the Baltimore classification system for viral genetic information. Viruses contain some form of DNA or RNA, but never both.
Viral genomic material can be comprised of which types of nucleic acids?
I. Single-stranded DNA
II. Double-stranded DNA
III. Single-stranded RNA
IV. Double-stranded RNA
I, II, III, and IV
I and II
III and IV
I and III
Explanation
Different classes of viruses store genetic material in different forms.
Double-stranded RNA (dsRNA) viruses, single-stranded RNA (ssRNA) viruses, double-stranded DNA (dsDNA) viruses, and single-stranded DNA (ssDNA) viruses are all large classes of viral classification. Retroviruses can be classified as ssRNA viruses, but are often left in their own category.
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 contains DNA; all viruses contain RNA
Neisseria does not have flagella; all viruses have flagella
Neisseria infects only one cell type; viruses have wide variety in their cellular targets
Explanation
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.
What molecule would you not expect to find in a retrovirus?
Thymine
Uracil
Adenine
Guanine
Cytosine
Explanation
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.
Polio is a highly infectious disease caused by the polio virus, which can be a debilitating disease in the worst case scenarios. The first effective vaccine for treating polio was developed by Jonas Salk at the University of Pittsburgh in 1952.
Salk's vaccine consisted of inactivated (dead) virus, administered orally. Which of the following statements is true regarding vaccines containing inactivated virus?
Vaccines containing inactivated viruses (if made correctly) have no chance of reactivating and causing an actual viral infection.
The process of inactivating viruses for these vaccines results in the exposure of more viral antigens, leading to a greater host immune response.
Generally, vaccines containing inactivated viruses only need a small dosage and no booster shots are necessary to achieve immunity.
These vaccines are highly immunogenic that adjuvants (a substance that enhances the host immune response to the antigen) are not needed.
None of these
Explanation
The process of inactivating live viruses results in dead (noninfectious) virus. In terms of safety (if the virus is inactivated correctly), inactivated virus vaccines have no risk of inducing a viral infection from the contents of the vaccine. In terms of effectiveness of inducing protective immunity, inactivated virus vaccines are typically less effective than attenuated but live virus vaccines. Therefore, the induction of long-term protective immunity against the virus is questionable. Inactivated virus vaccines normally require larger doses, multiple doses, and adjuvants to be effective.
Which of the following is not a component of HIV?
Ribosomes
Protein
RNA
Reverse transcriptase
Proteases
Explanation
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.