Question 1

A bacteriophage that is physically integrated into the host chromosome is called a ________.

Accepted Answer

When a bacteriophage integrates into the host chromosome, it becomes a prophage. A prophage can remain dormant and replicate along with the host chromosome until it is activated, at which point it enters the lytic cycle and produces new phages. An episome is a genetic element that can replicate and integrate into the host genome, but is not necessarily a bacteriophage. A virulent phage is a type of bacteriophage that always enters the lytic cycle and destroys the host cell. Capsid refers to the protein coat that surrounds the genetic material of a virus.

Question 2

Reverse transcriptase copies

Accepted Answer

Reverse transcriptase is an enzyme that copies RNA to DNA, making it essential in the process of reverse transcription. This process is used by retroviruses like HIV and some bacteria to replicate their genomes.

Question 3

Many scientists and drug companies have worked hard to produce drugs to stop various stages of the HIV life cycle. Some drugs have been tested that inhibit the function of Vpu. What stage of the HIV life cycle would such a drug inhibit?

Accepted Answer

The role of Vpu is to assist in the release of mature HIV particles from the infected cell by promoting virus budding. Inhibiting the function of Vpu would therefore inhibit the virus budding stage of the HIV life cycle.

Question 4

Select the phage λ proteins that function as antiterminators (check all that apply).

Accepted Answer

N and Q are the two phage λ proteins that function as antiterminators, while cII and cro regulate λ gene expression by other mechanisms.

Question 5

The reverse transcription of HIV RNA utilizes host cell tRNA as a primer. Specifically, a tRNA for lysine is utilized. Would a drug that blocked the host cell synthesis of the tRNA for lysine be a good drug to prevent the HIV life cycle?

Accepted Answer

Blocking the host cell synthesis of tRNA for lysine would disrupt the cell's ability to incorporate lysine into proteins, which is essential for cell survival and function. This would likely result in cell death, making it a poor strategy for targeting HIV without causing significant harm to the host.

Question 6

Gierer and Schramm isolated ________ from tobacco mosaic virus and applied it to plant tissue, which caused the same types of lesions that occurred when plants were exposed to intact tobacco mosaic virus.

Accepted Answer

Gierer and Schramm isolated RNA from tobacco mosaic virus and applied it to plant tissue, which caused the same types of lesions that occurred when plants were exposed to intact tobacco mosaic virus.

Question 7

Most biologists consider viruses to be living organisms, which are classified with bacteria.

Accepted Answer

Most biologists do not consider viruses to be alive because they cannot carry out metabolic processes on their own and require a host cell to replicate. Therefore, viruses are not classified with bacteria as living organisms.

Question 8

Because tobacco mosaic virus has an RNA genome, it must encode a reverse transcriptase.

Accepted Answer

Reverse transcriptase is an enzyme that synthesizes DNA from an RNA template. Since tobacco mosaic virus has an RNA genome, it does not need to encode a reverse transcriptase as it does not need to convert RNA into DNA.

Question 9

Select the viruses that can infect humans. Check all that apply.

Accepted Answer

Parvovirus, Influenza virus, and Epstein-Barr virus can infect humans.

Question 10

You are working in a lab that studies tobacco mosaic virus (TMV). You wish to perform follow up experiments to the Fraenkel-Conrat/Singer experiments. You use the Holmes ribgrass (HR) strain of TMV that they used, which produces streaks along the veins and contains histidine and methionine in the TMV capsid protein. You also use a second TMV strain that you've isolated, called Purp, that causes purple lesions on the leaves, and lacks histidine and methionine in the TMV capsid protein. If you use Purp RNA and HR proteins to create reconstituted viruses, what lesions do you expect will form, and what will the amino acid composition of the capsid protein be?

Accepted Answer

Since the Purp strain lacks histidine and methionine in the capsid protein, creating reconstituted viruses using HR proteins would result in a capsid protein without those amino acids. Additionally, the Purp strain causes purple lesions on the leaves, so the resulting reconstituted virus would also cause purple lesions rather than streaks along the veins. Therefore, the answer is B: Purple lesions, no histidine and methionine in the capsid protein.

Question 11

A ________ uses the lytic cycle to begin the immediate manufacture of new phages in the host cells.

Accepted Answer

Virulent phages have only one reproductive cycle, which is the lytic cycle, where they immediately begin to manufacture new phages in the host cells. Temperate phages can alternate between the lytic and lysogenic cycles, and bacteria and eukaryotic cells are not phages.

Question 12

The HIV genome is especially prone to mutation because

Accepted Answer

The HIV genome is prone to mutation because it is copied by reverse transcriptase, which lacks a proofreading function. This means that errors can accumulate during the replication process, resulting in genetic variation and the potential for drug resistance.

Question 13

A ________ frequently integrates into the host genome, forming prophages and utilizing a lysogenic cycle to manufacture new phages.

Accepted Answer

A temperate phage is a type of bacteriophage that is able to integrate into the host genome and remain in a dormant state, only undergoing the lytic cycle and producing new phages under certain conditions. This process is known as lysogeny and the integrated phage is called a prophage. In contrast, a virulent phage can only undergo the lytic cycle and immediately lyses the host cell to release new phages. Bacteria and eukaryotic cells do not integrate phages into their genomes.

Question 14

What is the correct order of the reproductive cycle of viruses?

Accepted Answer

The correct order of the reproductive cycle of viruses is Attachment-Entry-Integration-Synthesis of viral components-Viral assembly-Release. The virus must first attach to a host cell, then enter the cell, integrate into the host cell genome, and finally the host cell will synthesize viral components. The viral components will then assemble, and the newly formed viruses will be released from the host cell to infect other cells.

Question 15

If you created a strain of bacteria that overexpressed protease inhibitors, and then infected this bacteria with phage λ, would you expect the phage to follow the lytic or lysogenic cycle?

Accepted Answer

Protease inhibitors prevent degradation of proteins, including those involved in phage replication. This would make it more difficult for the lambda phage to enter the lytic cycle, as it relies on hijacking the host's replication machinery to make copies of itself. Therefore, the phage would be more likely to enter the lysogenic cycle in this scenario.

Question 16

The Gag polyprotein is cleaved into

Accepted Answer

The Gag polyprotein is specifically cleaved into structural proteins that are essential for the assembly and maturation of HIV virions, including the matrix protein, capsid protein, nucleocapsid protein, and p6.

Question 17

When phage λ enters the lytic cycle

Accepted Answer

When phage λ enters the lytic cycle, it undergoes a series of steps that lead to the production of many new copies of the phage genetic material and coat proteins. These new components are then assembled to make new phages. Finally, the host cell is lysed or ruptured, releasing the new phages into the environment.

Question 18

Latency in HIV occurs when

Accepted Answer

Latency in HIV occurs when the virus integrates into the host genome and remains dormant. During this state, the virus is not actively replicating or making new viral particles. Instead, the viral genome forms an episome and remains hidden in infected cells.

Question 19

What piece of the RNA HIV genome is used as a primer during the synthesis of double-stranded DNA from HIV RNA?

Accepted Answer

During the synthesis of double-stranded DNA from HIV RNA, a primer called the polypurine tract (PPT) is used to initiate reverse transcription. The PPT is located at the 3' end of the HIV genome and consists of a stretch of purine nucleotides (either adenine or guanine) followed by a few pyrimidine nucleotides (either cytosine or uracil). This sequence serves as a binding site for the reverse transcriptase enzyme that allows the copying of the RNA into DNA. Therefore, choice D, PPT, is the correct answer. tRNA is not used as a primer during HIV reverse transcription, although it does serve as a template for the synthesis of some viral proteins. U3 is a promoter region located at the 5' end of the HIV RNA genome, but it is not used as a primer during reverse transcription. The gag gene encodes for viral structural proteins, but it is not used as a primer during reverse transcription.

Question 20

Infectious mononucleosis is caused by the Epstein-Barr virus, and patients often exhibit a fever, sore throat, swollen glands, and fatigue for several weeks. In some patients, the virus can reactivate later and cause physical symptoms once again. This is likely because

Accepted Answer

The Epstein-Barr virus is known to have a latent phase where it remains in the body without causing symptoms. Reactivation of the virus during this phase can cause physical symptoms once again. This is different from being misdiagnosed or becoming sick again at the time the virus becomes latent. While there is still much research being done on the virus, it is not considered an emerging virus and we do have knowledge about its infectious life cycle.

Quiz 18: Genetics of Viruses