All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
Example Questions
Example Question #1 : Molecular Biology And Genetics
Which of the following is true about viral genomes?
Viral genomes are always circular
Viral genomes typically consist of 20,000+ genes
Viral genomes can be either RNA or DNA
Viral genomes are incapable of undergoing recombination events
Viral genomes can be either RNA or DNA
The human genome contains 20,000-25,000 genes, so, as one might expect, viral genomes are typically much smaller than this. Viral genomes can either be circular or linear, and both formats are susceptible to recombination events.
Different classes of viruses have different nucleic acid genomes. Double-stranded DNA, single-stranded DNA, double-stranded RNA, and single-stranded RNA can all be found in certain virions.
Example Question #2 : Molecular Biology And Genetics
An inhibitor that prevents reverse transcription would be most useful in combatting which of the following viruses?
I. Retroviruses
II. DNA viruses
III. RNA viruses
I and III
I, II, and III
III only
I only
I only
Of the three choices, only retroviruses use reverse transcription to make a DNA copy of their RNA genomes.
DNA viruses do not need to do this because their genome already consists of DNA. RNA viruses use specialized enzymes called RNA replicases to make RNA copies of their RNA genomes, and do not go through a DNA intermediate like retroviruses.
Example Question #3 : Molecular Biology And Genetics
Which type of virus uses reverse transcriptase in order to convert its genome into a viable template for reproduction?
Single-stranded DNA viruses
Retroviruses
Single-stranded RNA viruses
Double-stranded RNA viruses
Retroviruses
Reverse transcriptase is used to convert RNA genomes into DNA genomes. The genome is then inserted into the host's chromosomes, where it can be transcribed numerous times to create viral proteins. Without this process, the RNA genome would have a very short-lived existence in the cell, resulting in very few viral copies.
This technique is used by retroviruses, such as HIV.
Example Question #4 : Molecular Biology And Genetics
Which of the following is the correct sequence for viral replication?
Viral assembly, release, penetration, transcription, protein synthesis, replication
Replication, viral assembly, transcription, protein synthesis, penetration, release
Transcription, protein synthesis, replication, viral assembly, release, penetration
Release, replication, transcription, protein synthesis, viral assembly, penetration
Penetration, replication, transcription, protein synthesis, viral assembly, release
Penetration, replication, transcription, protein synthesis, viral assembly, release
The first step in viral replication is penetration. The virus may be engulfed by the host cell or fuse with the host's membrane. The viral genetic material is released into the cytoplasm. During replication the viral genetic material is copied many times. The viral genetic material is used as a blueprint to make messenger RNA (mRNA) during the transcription stage. The mRNA is used to synthesize viral proteins. The viral genetic material and enzymes are surrounded by their protein coat during viral assembly. Finally viruses are released from the host cell by budding from the cell membrane or bursting the cell.
Example Question #5 : Molecular Biology And Genetics
Why do viral proteins interact with each other extensively as well as interact with a wide array of host proteins?
To modulate host cellular activities
All of these
Viral proteins exhibit numerous, small, low-specificity binding sites
Viral proteins have many splice variants
Viruses encode a small number of proteins compared to the host
All of these
All of the answers are correct. Given that viral genomes are small, the proteins that they encode must be able to execute many functions. Due to high mutation rate, many splice variants, and multiple small protein binding domains, viral proteins interact extensively with each other and host proteins. This allows viral proteins to modulate host cellular activities such as inflammation, proliferation, anti-viral response, and DNA replication/transcription/translation so that viral proteins are able to replicate and are not killed by the infected cells.
Example Question #6 : Molecular Biology And Genetics
What enzyme would a non retroviral RNA virus use to replicate it's genome?
An RNA dependent DNA polymerase encoded by the virus
An RNA dependent RNA polymerase encoded by the virus
A DNA dependent RNA polymerase encoded by the virus
An RNA dependent RNA polymerase encoded by the host
A DNA dependent RNA polymerase encoded by the virus
An RNA dependent RNA polymerase encoded by the virus
In order the replicate its genome, a non retroviral RNA virus must use a polymerase that can use an RNA template to polymerize a complimentary RNA molecule; an RNA dependent RNA polymerase. Since no such enzyme exits in host cells, the virus must encode this enzyme itself.
Example Question #7 : Molecular Biology And Genetics
___________ is a term used to describe a viral lifecycle in which the virus incorporates its DNA into the host's genomic DNA.
Invasive
Lysogenic
Lytic
Latent
Lysogenic
Lytic viral lifecycles involve using the host's machinery to mass produce further copies of the virus.
Lysogenic lifecycles can become lytic under the right circumstances. The key difference is the time period and method of infection. In the lysogenic cycle, viral DNA is incorporated into the host genome and remains dormant, rather than becoming active immediately to generate more virions. After a period of time the viral DNA will be synthesized in large quantities, transitioning into the lytic cycle, and eventually lysing the cell.
Latent is a term used to refer to the period when a virus lays dormant within a host. Invasive is not a term commonly used to refer to a viral lifestyle.
Example Question #8 : Molecular Biology And Genetics
Which event is not part of the viral lytic life cycle?
New viruses are assembled inside of the cell
Viral DNA is integrated into the chromosome
The virus uses host ribosomes to create viral proteins
Viral nucleic acid is injected into the cell
Viral DNA is integrated into the chromosome
The lytic life cycle is the most basic life cycle for a virus. The virus injects its nucleic acid into the host, synthesizes the parts needed for new viruses using the host cell's ribosomes, assembles the viruses, and then breaks out of the host cell (lysis).
At no point in the lytic life cycle will a virus integrates its genome into the host's chromosomes. This technique is employed by viruses with a lysogenic life cycle.
Example Question #9 : Molecular Biology And Genetics
Which of the following statements about viral life cycles are true?
It takes a bacteriophage roughly three hours from binding and infecting a host cell to lysing it
Viruses that enter the lytic cycle exist as prophages
Temperate viruses are those that can infect a cell that has already been infected by another virus
Once a phage injects its nucleic acid into the host cell, the lytic cycle consists of two stages
Virulent viruses reproduce only by the lysogenic cycle
Once a phage injects its nucleic acid into the host cell, the lytic cycle consists of two stages
Virulent viruses are those that reproduce only by the lytic cycle. It takes a bacteriophage only ~30 minutes to complete a lytic cycle. Prophages are latent forms of lysogenic bacteriophages that are incorporated into the host genome. Prophages can remain inactive within the genome through may cell divisions. Temperate viruses are those that may display lysogeny. Once a phage injects its nucleic acid into the host cell, the lytic cycle consists of two stages. In the early stage, transcription of viral genes that code for shutting down host transcription. In the late stage, viral genes are transcribed which code for capsid proteins and proteins that lyse the host cell to release the new viruses.
Example Question #10 : Molecular Biology And Genetics
A virus that causes cell lysis undergoes the __________ cycle and a virus that induces inflammation undergoes __________ cycle.
lysogenic . . . lytic
lytic . . . lytic
lytic . . . lysogenic
lysogenic . . . lysogenic
lytic . . . lytic
There are two types of viral life cycles. First, a virus enters the host cell, replicates, lyses the cell, and infects another host cell. This life cycle is called the lytic cycle and results in immediate infection, symptoms, and immune response (such as inflammation). Second, a virus can enter the host cell, incorporate itself into the host cell’s genome, and stay latent for years. This life cycle is called the lysogenic cycle and it can take years for symptoms to appear. Symptoms occur when the inactive virus is activated due to some environmental cue. The virus gets activated, replicates, lyses the cell, and causes infection.
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