Question 1

The genome of influenzavirus is

Accepted Answer

The genome of the influenza virus consists of multiple pieces of linear single-stranded RNA (ssRNA), making it a segmented RNA virus. This allows for reassortment of its genome segments, which can lead to the emergence of new viral strains.

Question 2

Which of the following lists stages of a lytic replication cycle in order, from earliest to latest stages?
I. Synthesis
II. Assembly
III. Attachment
IV. Release
V. Entry

Accepted Answer

The correct order for the stages of a lytic replication cycle is: Attachment (III), Entry (V), Synthesis (I), Assembly (II), and Release (IV).

Question 3

How are fungal viruses transmitted?

Accepted Answer

Fungal viruses, also known as mycoviruses, are typically transmitted through the fusion of cells or hyphae, a process inherent to the growth and reproduction of fungi. This mode of transmission allows the virus to spread within fungal colonies or between closely interacting fungi.

Question 4

Which of the following is primarily responsible for the shape of a virion?

Accepted Answer

The capsid is the protein shell that surrounds the viral genome and is primarily responsible for the shape of a virion. Different viruses have different types of capsids, such as icosahedral or helical, which give them their distinct shapes.

The other options do not directly affect the shape of a virion. The type of nucleic acid and number of segments may affect the genetic composition of the virus, but not its physical shape. The source of the envelope may determine whether the virus is enveloped or non-enveloped, but not the shape of the virion. The specific host protein the virus targets may determine the host range of the virus, but again, not its shape.

Question 5

Which of the following statements regarding virus taxonomy is true?

Accepted Answer

It is true that some virus family names are derived from the name of an important member of the family, such as the Togaviridae family, which is named after the genus Togavirus. The other options given are incorrect.

Question 6

Which of the following is associated with the attachment of a bacteriophage to a bacterial cell?

Accepted Answer

Bacteriophages attach to bacterial cells through a process that involves random collisions, chemical attractions, and receptor specificity. Random collisions bring the phage close to the bacterial surface, chemical attractions help the phage to adhere to the cell, and receptor specificity ensures that the phage attaches only to specific bacteria that have the right receptor molecules on their surface.

Question 7

A(n) ________ is a virus that infects bacterial cells.

Accepted Answer

A bacteriophage is a type of virus that infects and replicates within a bacterial host cell. They are also known as bacterial viruses. A virion is a complete viral particle outside of a host cell, a prion is a misfolded protein that can cause diseases, a nucleocapsid is the genetic material of a virus surrounded by a protein shell, and an envelope is a lipid membrane that surrounds some viruses.

Question 8

Which of the following is a characteristic by which viruses are classified?

Accepted Answer

Viruses are classified based on the type of nucleic acid they possess, whether it is DNA or RNA. This is an important characteristic as it determines the replication and transcription mechanisms of the virus. Other characteristics such as size, host range, and life cycle are also considered, but they do not play as significant a role in classification as the type of nucleic acid.

Question 9

Host specificity of a virus is due to

Accepted Answer

Host specificity of a virus is primarily due to interactions between viral and cellular surface molecules, such as receptors on the host cell's surface that the virus can recognize and bind to. This is why different viruses tend to infect different types of cells and organisms. The other options are not generally relevant to host specificity.

Question 10

The outermost layer of a virion fulfills which of the following functions of the virus?

Accepted Answer

The outermost layer of a virion, also called the envelope or capsid, serves both protection and recognition functions. It protects the genetic material of the virus and aids in its transmission, as well as plays a crucial role in recognition and attachment to host cells. It does not directly participate in replication, which occurs within the host cell after the virus has gained entry.

Question 11

A(n) ________ is a bacterial virus which is integrated into the host cell DNA.

Accepted Answer

A prophage is a type of bacteriophage that has integrated into the host cell's DNA and remains there as a dormant state. During Lysogenic cycle, the prophage DNA replicates along with the cell's DNA and is passed on to daughter cells during cell division.

Question 12

The enzyme lysozyme is critical for which of the stages of a bacteriophage T4 infection cycle?

Accepted Answer

Lysozyme is critical for both the entry and release stages of a bacteriophage T4 infection cycle. In the entry stage, lysozyme weakens the peptidoglycan layer of the bacterial cell wall, allowing the phage to inject its genetic material into the host cell. In the release stage, lysozyme breaks down the bacterial cell wall, allowing the newly assembled phages to escape and infect other cells.

Question 13

In what ways do viruses differ from other pathogens?

Accepted Answer

Unlike other pathogens, such as bacteria or fungi, viruses do not have cytoplasm and organelles. They are essentially small packets of genetic material surrounded by a protein coat.

Answer: E 
 Viruses are composed of both protein and lipid. While their protein coat provides protection and can aid in host cell recognition, their genetic material is often encased by a lipid envelope that can help the virus evade detection by the host's immune system.

Question 14

Which of the following agents is capable of inducing conversion of a prophage to the lytic cycle?

Accepted Answer

Both UV light and X rays can induce the SOS response in bacteria, leading to the prophage entering the lytic cycle.

Question 15

Replication of most ________ viruses is similar to normal cellular processes.

Accepted Answer

dsDNA viruses replicate in a manner similar to the normal cellular process, using the host's replication machinery to synthesize new DNA.

Question 16

Which of the following events occurs in the lytic cycle of bacteriophage T4 infection but not in the lysogenic cycle?

Accepted Answer

In the lytic cycle, the bacteriophage T4 immediately begins to digest the host DNA using its own enzymes to take over the bacterial host. This destruction of host DNA does not occur in the lysogenic cycle. The other events (attachment, entry, viral protein synthesis) occur in both the lytic and lysogenic cycles.

Question 17

Why is lysogeny advantageous to a bacteriophage?

Accepted Answer

Lysogeny allows the viral genetic material to be integrated into the host cell's genome, where it can be replicated along with the host DNA during cell division. This results in a much larger pool of viral genetic material, which can be advantageous for the bacteriophage in certain situations, such as when the host bacterial population is relatively small or when environmental conditions are unfavorable for viral replication.

Question 18

Which of the following is CORRECT regarding the viral envelope?

Accepted Answer

The viral envelope is composed of the cellular phospholipid membrane of the host cell and also contains both cellular and viral proteins. This enables the virus to fuse with the host cell membrane during infection and facilitates the release of newly formed virions from the host cell.

Question 19

Attachment of herpesviruses results in ________, a process in which the host cell facilitates viral entry.

Accepted Answer

Attachment of herpesviruses typically results in endocytosis, in which the virus is engulfed by the host cell and enters through a vesicle. This process is facilitated by host cell receptors and is different from direct penetration or membrane fusion, which are other modes of viral entry. Exocytosis is a process by which the cell releases contents to the outside, and lysogeny refers to the integration of viral DNA into the host genome.

Question 20

Which of the following is NOT used for the classification of viruses?

Accepted Answer

The classification of viruses does not use the term "class." The taxonomy of viruses is divided into order, family, genus, and species, with specific epithets sometimes added to further describe the virus.

Quiz 13: Characterizing and Classifying Viruses, Viroids, and Prions