Question 1

- In the figure, when new viruses are being assembled at the point marked IV, what mediates the assembly?

Accepted Answer

D

Question 2

Which of the following descriptions correctly identifies the main structural differences between viruses with envelopes and viruses without envelopes?

Accepted Answer

The main structural difference between viruses with envelopes and viruses without envelopes is that viruses with envelopes have a phospholipid membrane outside their capsid, whereas viruses without envelopes do not have a phospholipid membrane. Both types of viruses have a capsid and genetic material enclosed by a layer made of protein. However, in viruses without envelopes, the genetic material is directly enclosed by the protein layer, while in viruses with envelopes, the genetic material is inside both the protein layer (capsid) and the phospholipid membrane.

Question 3

The herpesviruses are important enveloped DNA viruses that cause disease in vertebrates and in some invertebrates such as oysters. Some of the human forms are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can later reactivate, replicate again, and infect others.
In electron micrographs of HSV infection, it can be seen that the intact virus initially reacts with cell-surface proteoglycans, then with specific receptors. This is later followed by viral capsids docking with nuclear pores. Afterward, the capsids go from being full to being "empty". Which of the following statements best fits these observations?

Accepted Answer

The observation that the intact virus initially reacts with cell-surface proteoglycans and specific receptors implies that the viral envelope mediates entry into the cell. The fact that the capsids dock with nuclear pores and become "empty" suggests that the capsid mediates entry into the nuclear membrane and that only the genome enters the nucleus. This option is best represented by choice D.

Question 4

Which of the following characteristics correctly describes retroviruses?

Accepted Answer

Retroviruses have a single-stranded RNA genome that acts as a template for DNA synthesis through the action of reverse transcriptase enzyme. This DNA is then integrated into the host genome, allowing the virus to replicate along with the host cell. Retroviruses are not made up of a single protein, and they do not infect bacteria, so choices A and B are incorrect. Retroviruses do not have a single-stranded DNA genome, so choice C is also incorrect.

Question 5

-Which of the three types of viruses shown in the figure would you expect to include a capsid(s)?

Accepted Answer

All three types of viruses shown in the figure (I, II, and III) have a capsid. The capsid is the protein coat that surrounds the viral genome in all viruses.

Question 6

-In the figure, at the arrow marked II, what enzyme is being utilised?

Accepted Answer

At the arrow marked II, the host cell DNA polymerase is being utilized to synthesize a new strand of DNA complementary to the viral RNA template.

Question 7

Which of the following processes can viruses carry out?

Accepted Answer

Viruses lack the machinery to carry out metabolic processes or produce ATP, proteins, or nucleic acids on their own. They rely on host cells to replicate themselves and make viral proteins.

Question 8

- Which of the three types of viruses shown would you expect to include glycoproteins?

Accepted Answer

The answer of  
- Which of the three types...

Question 9

Which of the following statements supports the argument that viruses are nonliving?

Accepted Answer

One of the defining characteristics of living organisms is that they can carry out metabolic processes, such as obtaining and utilizing energy. Viruses cannot carry out these processes on their own and must rely on host cells to do so.

Question 10

What is the function of reverse transcriptase in retroviruses?

Accepted Answer

Reverse transcriptase is the enzyme responsible for synthesizing a complementary DNA strand using viral RNA as a template in retroviruses. This process is called reverse transcription, and it is a key step in the retroviral life cycle.

Question 11

The host range of a virus is determined by ________.

Accepted Answer

The host range of a virus is determined by the specific proteins on its surface that can recognize and bind to specific proteins on the surface of the host cell. This interaction is necessary for the virus to enter the host cell and infect it. Therefore, the answer is D, as the proteins on the surface of the virus and the host determine the host range of the virus.

Question 12

Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. At its 5′ end, the RNA genome has a viral protein (VPg) instead of a 5′ cap. This is followed by a non-translated leader sequence, and then a single long protein-coding region (~7,000 nucleotides), followed by a poly-A tail. Observations were made that used radioactive amino acids similar in structure to those that are found in viruses and other organisms. Short-period use of the radioactive amino acids result in labelling of only very long proteins, while longer periods of labelling result in several different short polypeptides.
What conclusion is most consistent with the results of the radioactive labelling experiment?

Accepted Answer

The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones.

Question 13

Which of the following events or characteristics accounts for someone who has had regular herpesvirus-mediated cold sores or genital sore flare-ups?

Accepted Answer

Herpesviruses are capable of establishing latent infections where viral genomes persist in host nuclei as stable, circular episomes. In this state, viral genes are not expressed but viral DNA can be reactivated periodically leading to recurrent infections. Therefore, regular herpesvirus-mediated cold sores or genital sore flare-ups are the result of reactivation of the latent viral genome in host nuclei, not reinfection by the same or a different strain of herpesvirus.

Question 14

Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. The intact cells were removed from the sample, and the number of viruses per millilitre of culture was determined.
-Using the data in the figure, how long does it take for virus B to go through one lytic cycle?

Accepted Answer

The answer of  Cells were infected with approximately 1,000...

Question 15

Which of the following characteristics is typical of the lytic cycle of a bacteriophage?

Accepted Answer

The lytic cycle of a bacteriophage involves the destruction of the host cell, and as a result, a large number of phages are released at once. The viral DNA is not usually incorporated into the host genome, and the virus-host relationship is not typically long-lasting.

Question 16

Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. The intact cells were removed from the sample, and the number of viruses per millilitre of culture was determined.
-Using the data in the figure, how long does it take for virus A to go through one lytic cycle?

Accepted Answer

The answer of  Cells were infected with approximately 1,000...

Question 17

In many ways, the regulation of the genes of a particular group of viruses will be similar to the regulation of the host genes. Therefore, which of the following regulation mechanisms would you expect of the genes of a bacteriophage?

Accepted Answer

The answer of In many ways, the regulation of the...

Question 18

The virus genome and viral proteins are assembled into virus particles during which of the following parts of the reproductive cycle?

Accepted Answer

The assembly of virus particles is a step in the lytic cycle, where the virus takes over the host machinery to make new virus particles and eventually leads to the lysis of the host cell. The lysogenic cycle involves the integration of the viral genome into the host genome without immediately causing cell lysis, and there is no assembly of virus particles during this stage. Therefore, the correct choice is C, which states that assembly occurs during the lytic cycle only.

Question 19

Which of the following statements accurately describes the lysogenic cycle of lambda (λ) phage?

Accepted Answer

During the lysogenic cycle of lambda (λ) phage, the phage DNA is integrated into the host chromosome, where it is replicated along with the host genome. Instead of immediately causing the host cell to produce viruses, the prophage may remain dormant until a later time when it enters the lytic cycle.

Question 20

Some viruses can be crystallised and their structures analysed. One such virus is yellow mottle virus, which infects beans. This virus has a single-stranded RNA genome containing about 6,300 nucleotides. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. If the yellow mottle virus begins its infection of a cell by using its genome as mRNA, which of the following would you expect to be able to measure when analysing the reproduction of this virus?

Accepted Answer

If the yellow mottle virus begins its infection of a cell by using its genome as mRNA, it means that the virus skips the step of transcription and directly uses its RNA genome for translation. Therefore, measuring the translation rate would provide insight into the reproduction of the virus. Replication rate (A), transcription rate (B), and formation of new transcription factors (D) would not be directly relevant in this scenario.

Quiz 19: Viruses