Question 1

A virus that follows the lysogenic cycle can often be considered easier to manage. Explain why this is so.

Accepted Answer

Answers may vary. Lysogenic viruses are ones that will attack the host cell in a relatively short time frame after the infection. The host will become aware that they have the virus and can seek treatment. A lytic virus can "hide" within the host cells and not make their appearance for quite some time. This is a type of virus that can go latent and not be expressed. It will incorporate the viral DNA into the host's DNA.

Question 2

If a virus is latent, it

Accepted Answer

Latent viruses are not actively replicating or causing symptoms in the host. Retroviruses refer to viruses that use reverse transcriptase to convert their RNA genome into DNA, which is then integrated into the host cell's genome. This is not related to latency. Lysogenic cycles refer to the integration of a virus's genome into the host cell's genome, whereas latent viruses do not necessarily integrate their genome into the host cell's genome. The process of "budding" is a method by which some enveloped viruses acquire their outer coat; this is also not related to latency. Developing immunity against a virus is not necessarily related to whether it is latent or not.

Question 3

The cycle of viral infection in which the viral DNA is integrated into the host's DNA is called the _______ cycle.

Accepted Answer

The lysogenic cycle is the cycle of viral infection where the viral DNA is integrated into the host's DNA. In this cycle, the virus does not immediately cause the host cell to die, but instead the viral DNA is replicated along with the host's DNA during cell division, allowing the virus to be transmitted to the host's offspring.

Question 4

Pasteur chose the Latin root word for "virus" meaning

Accepted Answer

The Latin root word for "virus" means "poison." Louis Pasteur, a pioneering microbiologist, chose this term due to the harmful effects of viruses, which were not well understood at the time but were recognized for their ability to cause disease, akin to a poison.

Question 5

Which of the following could be used to grow lysogenic viruses in the laboratory?

Accepted Answer

Lysogenic viruses can integrate their genome into the host's DNA, and they can infect a wide range of hosts, including animals (hence chicken eggs), cultured cells (cell culture), and bacteria. Therefore, all the listed methods are applicable for growing lysogenic viruses.

Question 6

Which statement is NOT true about a retrovirus?

Accepted Answer

Retroviruses are unique in that they integrate a cDNA copy of their genome into the host cell genome, but this integrated provirus is replicated along with the host DNA during cell division. Therefore, retroviruses can persist in host cells for extended periods of time, and can even be passed on to daughter cells during cell division.

Question 7

Many microbiologists prefer to describe viruses as being "activated" rather than "living." Consider again the discussion of "properties of life" and describe at least three distinct reasons why the term "activated" is more appropriate.

Accepted Answer

The answer of Many microbiologists prefer to describe viruses as...

Question 8

Which of the following is not part of the reproduction cycle of HIV?

Accepted Answer

HIV does not undergo reverse transcription of viral DNA. The virus's replication cycle involves reverse transcription of its RNA genome into DNA, not the reverse transcription of viral DNA.

Question 9

An enveloped virus enters a host cell by

Accepted Answer

Enveloped viruses have a lipid envelope around their protein coat. This envelope allows the virus to fuse its membrane with the host cell's plasma membrane, allowing the viral genetic material to enter the host cell. This process is called membrane fusion and is the most common way that enveloped viruses infect host cells. Therefore, choice B is the correct answer.

Question 10

Which of these is the best description of a virus?

Accepted Answer

A virus is not considered to be a living organism because it cannot replicate or carry out metabolic processes on its own. It consists of a genetic material (either RNA or DNA) enclosed in a protective protein shell known as a capsid.

Question 11

Influenza strains that sweep around the world often carry names such as Shanghai H₁N₁ or Mexico City H₂N₂. The viruses vary in H and N surface proteins because

Accepted Answer

Influenza viruses mutate frequently, leading to the emergence of new strains that can evade the immunity of previously infected individuals. Highly populated areas act as hotspots for the spread of these new strains, which can then sweep around the world, leading to the emergence of viruses with different combinations of H and N surface proteins. Therefore, option D is the correct answer.

Question 12

What is the correct sequence of events in the lytic cycle of a bacteriophage infection?

Accepted Answer

The correct sequence in the lytic cycle of a bacteriophage infection is attachment, viral DNA penetration, biosynthesis, maturation, and release. Option A is incorrect as there is no integration of viral DNA into the host cell DNA during the lytic cycle. Option B is incorrect as it describes the process of a virus infecting an animal cell, not a bacteriophage infecting a bacterial cell. Option C is incorrect as fusion of the envelope and host cell membrane only occurs in enveloped viruses, which bacteriophages are not.

Question 13

Describe the lysogenic cycle of a bacteriophage and/or a prophage. Why do you think it would be useful to the virus to have this cycle.

Accepted Answer

The answer of Describe the lysogenic cycle of a bacteriophage...

Question 14

In order to infect a cell, a virus must

Accepted Answer

In order to infect a cell, a virus must have a special protein on its surface that can interact with a protein on the surface of the host cell. This interaction allows the virus to attach to and enter the host cell, where it can then use the host's cellular machinery to replicate and spread to other cells.

Question 15

Viruses are categorized according to all of the following EXCEPT

Accepted Answer

Viruses are not categorized based on their method of reproduction as they are obligate intracellular parasites that require a host cell to replicate, and therefore do not possess their own reproductive machinery. Their categorization is based on size and shape, type of nucleic acid (DNA or RNA), and the presence or absence of an envelope.

Question 16

Some, but not all, virus capsids are surrounded by _________.

Accepted Answer

Some viruses have a membranous envelope surrounding their protein capsid, but this is not a characteristic of all virus capsids.

Question 17

The cycle of viral infection of a bacterial cell that will cause its death most rapidly is called the _______ cycle.

Accepted Answer

The lytic cycle is a rapid cycle of viral infections that causes the death of the bacterial cell. In this cycle, the virus immediately takes over the host's cellular machinery to produce more viruses, which then lyse (burst) the host cell, releasing the new viruses to infect other cells. The lysogenic cycle is a slower cycle where the viral DNA integrates into the bacterial genome and replicates along with it, potentially remaining dormant for a long time before initiating the lytic cycle. Lysozyme is an enzyme that breaks down bacterial cell walls, lysol is a disinfectant, and lysosome is a cellular organelle involved in digestion.

Question 18

Ivanowsky first recognized that something smaller than a bacterium, called a filterable virus, was able to cause disease in the year

Accepted Answer

Ivanowsky first recognized the filterable virus in 1892.

Question 19

What are the two Domains that the prokaryotes are classified under?

Accepted Answer

Prokaryotes are classified into two domains, Archaea and Bacteria. The other options are not correct because Protista is a domain that includes eukaryotic organisms, and both Eukarya and Archaea include eukaryotic organisms, which are not prokaryotic.

Question 20

The innermost portion of a virus' structure is made up of

Accepted Answer

The innermost portion of a virus' structure is its genetic material, which can be either DNA or RNA.

Answer: D 
 Surrounding the genetic material of a virus is a protein capsid, which protects the genetic material and helps the virus attach to host cells. A membranous envelope and spikes may be present in some viruses, but they are not part of the innermost structure.

Quiz 20: Viruses, Bacteria, and Archaea