Question 1

The segmentation of the influenza genome is conducive to ________, which can be defined as the process by which two different viruses swap genome segments to form a new genome.

Accepted Answer

The segmentation of the influenza genome allows for reassortment to occur. Reassortment is the process by which two different influenza viruses can infect the same cell and swap genome segments to form a new reassorted genome. This is a common mechanism for the emergence of novel influenza viruses, such as pandemic strains.

Question 2

The HIV genome can be characterized by all of the following EXCEPT

Accepted Answer

HIV, being a retrovirus, uses an RNA genome for its replication and does not use a DNA primer. Instead, it uses a tRNA molecule as a primer for reverse transcription to synthesize DNA from its RNA genome.

Question 3

Which of the following is FALSE regarding the establishment of lysogeny?

Accepted Answer

Rolling-circle replication is not involved in the establishment of lysogeny. Instead, lambda phage DNA integrates into the host genome at the att site by site-specific recombination. The repressor CI produced by the integrated prophage prevents superinfection by other lambda phages, and it binds to the major groove of a specific DNA sequence in the bacterial host to prevent the transcription of lytic promoters. Once integrated, the prophage may express a limited number of genes, including the repressor C1.

Question 4

The director of a laboratory in charge of making the flu vaccine for the upcoming season is planning her production strategy. She must consider the phenomenon of reassortment, in which

Accepted Answer

Reassortment occurs when two different viruses infect the same cell and exchange genome segments, resulting in a new virus with a segmented genome that is a mix of the two original viruses. This is distinct from recombination (B), which involves the formation of a new genetic molecule from two different molecules, and from mutation processes (C, E) or antigenic shift (D) which involve different mechanisms of genetic change.

Question 5

The figure below is a transmission electron microscopy image of an influenza A virion. Hemagglutinin (HA) is one of the spike proteins. Which is the other spike protein on the envelope of influenza A?

Accepted Answer

The other spike protein on the envelope of influenza A is neuraminidase. This is shown in the figure, where the HA protein is labeled and the other spike protein (neuraminidase) is labeled as NA.

Question 6

RNA synthesis of influenza virus is primed by 7-methylguanine fragments of host mRNA, obtained by

Accepted Answer

Influenza virus RNA synthesis is primed by a process called cap-snatching, where the virus steals the 7-methylguanine fragments (also known as the cap) from the 5' end of the host mRNA. This serves as a primer for the virus's own RNA synthesis.

Question 7

The figure below shows a partial map (0 to about 22 kbp) of the lambda DNA genome. Which gene or gene set is mislabeled?

Accepted Answer

The answer of The figure below shows a partial map...

Question 8

What is the cause for cloudy centers appearing in lambda plaques on an Escherichia coli confluent plate?

Accepted Answer

Some infected cells become lysogens, meaning they incorporate the bacteriophage DNA into their own genome and do not lyse. Instead, they continue to grow, leading to the cloudy centers observed in lambda plaques. This phenomenon is characteristic of temperate phages like lambda, which can enter either a lytic or lysogenic cycle upon infecting a bacterium.

Question 9

The lambda genome is replicated by a rolling circle mechanism. What is the end result after a round of replication?

Accepted Answer

The rolling circle mechanism of lambda genome replication results in concatemers, or multiple genomes joined end-to-end, which are cleaved at specific cos sites by the terminase enzyme. This produces linear, double-stranded DNA that is eventually packaged into the phage head. Therefore, choice D is the correct answer. The other choices are incorrect as they do not accurately describe the replication and packaging of the lambda genome.

Question 10

Which host protein cleaves CI and triggers up to 100% lysis after lysogenic Escherichia coli cells are exposed to ultraviolet light?

Accepted Answer

RecA is a host protein that cleaves CI and triggers up to 100% lysis after lysogenic Escherichia coli cells are exposed to ultraviolet light. This cleavage is part of the SOS response, which is activated by DNA damage and leads to the induction of multiple genes, including those encoding RecA and proteases such as Lon protease. However, RecA is the key player in this process as it promotes the autocleavage of CI, which in turn leads to the expression of the lytic genes and consequent lysis of the cell. Primase, DNA polymerase III and terminase are all involved in DNA replication and packaging, but not in the regulation of lysogeny and lysis.

Question 11

Influenza shows cyclic appearance of extremely virulent strains that may cause widespread infection with high mortality, such as that of 1918, which infected 20% of the world's population and killed more people than World War I. What is this type of infection called?

Accepted Answer

The type of infection described is a pandemic, which refers to a global outbreak of a disease affecting a large number of people. It is characterized by the appearance of a new strain of a virus that has not been previously identified and for which there is no immunity in the population. In contrast, an epidemic refers to a sudden increase in the number of cases of a disease above what is normally expected in a specific geographic area or population, while endemic refers to a disease that is consistently present in a certain region or population. Mutagenic and transgenic are not related to the cycle of appearance of strains in influenza.

Question 12

Proteolysis of the influenza ________ produces a fusion peptide, which initially binds to a ________ glycoprotein on the host's cell membrane that serves as a receptor.

Accepted Answer

Proteolysis of the influenza hemagglutinin produces a fusion peptide, which initially binds to a sialic acid glycoprotein on the host's cell membrane that serves as a receptor.

Question 13

The term "________" describes the mutation-caused emergence of multiple viral strains that present differing properties of replication, tissue tropism, and drug resistance within a single infected individual.

Accepted Answer

The term "quasispecies" specifically refers to mutant swarms of viruses that emerge within a single host due to the high variability of RNA viruses and the error-prone replication process. Quasispecies can present different properties such as replication efficiency, tissue tropism, and drug resistance, making them challenging to control with antiviral therapies.

Question 14

What vertebrate groups harbor influenza viruses capable of mutating into strains infective to humans?

Accepted Answer

Influenza viruses capable of mutating into strains infective to humans are known to be harbored by both birds and swine. This is because these animals are capable of being infected with both avian and human influenza viruses, leading to the potential for reassortment and the creation of a new virus that can infect humans. Other animals may also harbor influenza viruses, but they may not be as likely to mutate in a way that allows them to infect humans.

Question 15

The capsid of the bacteriophage lambda is composed of two types of protein subunits, namely, D and E, arranged in a(n)________ shape.

Accepted Answer

Icosahedral shape is commonly found in viral capsids, including bacteriophage lambda. The icosahedral shape is made up of 20 equilateral triangles, which can be further subdivided into smaller triangles. This allows for efficient packaging of the genome and provides stability to the capsid.

Question 16

The neuraminidase inhibitor ________ is currently used to treat influenza infections.

Accepted Answer

Tamiflu is a neuraminidase inhibitor and is currently used to treat influenza infections. Pleconaril is an antiviral medication used to treat enterovirus infections, Zidovudine is used to treat HIV infections, Acyclovir is used to treat herpesvirus infections, and Vitravene is used to treat cytomegalovirus infections, none of which are treated with a neuraminidase inhibitor.

Question 17

The genome of the influenza virus is best described as

Accepted Answer

The genome of the influenza virus is comprised of (-) strand segmented RNA. This means that the genome is made up of multiple segments of RNA that are complementary to the (+) strand RNA which acts as the viral mRNA.

Question 18

The figure below shows a partial map of the lambda DNA genome (23-48 kb). The early left and right operons as well as the late operon are indicated. Which gene or gene set is mislabeled?

Accepted Answer

The answer of The figure below shows a partial map...

Question 19

Control proteins Cro and CII lead to lysis or lysogeny, respectively. What environmental signal in the host contributes to regulate the amount of CII by influencing the activity of the protease HflB?

Accepted Answer

Nutrient concentrations in the host cell influence the activity of the protease HflB, which in turn regulates the stability and amount of the CII protein, affecting the decision between lysis and lysogeny in bacteriophage lambda.

Question 20

Which of the following statements is FALSE regarding phage lambda as a temperate phage?

Accepted Answer

The statement "Lambda phage immediately kills its host after infection" is false. Lambda phage can integrate into the bacterial genome and establish lysogeny, in which the prophage replicates along with the host cell and does not cause lysis. Alternatively, lambda can enter into the lytic cycle and cause host cell lysis to release virions.

Quiz 11: Viral Molecular Biology