$$\mathrm{RNA} \xrightarrow{\text{reverse transcriptase}} \mathrm{DNA}$$

$$\text{Phage DNA} + \text{Host DNA} \xrightarrow{\text{integrase}} \text{Prophage}$$

Question 1

Which experiment provided definitive evidence that RNA is the genetic material of Tobacco Mosaic Virus (TMV)?

Accepted Answer

Mixing purified TMV RNA with HR capsid proteins and observing that the progeny virus phenotype matched the RNA source, not the protein source.

Question 2

A virus with a polyhedral capsid, protein fibers with knobs, and a DNA genome is most likely:

Accepted Answer

Adenovirus

Question 3

Which step is NOT part of the general viral reproductive cycle?

Accepted Answer

Translation of host cell mRNA

Question 4

During the lysogenic cycle of bacteriophage lambda, which protein is primarily responsible for maintaining latency by repressing lytic genes?

Accepted Answer

Lambda repressor (cI)

Question 5

Starvation conditions in E. coli favor the lysogenic cycle of phage lambda because:

Accepted Answer

Cellular proteases are less active, allowing cII protein to accumulate and activate the PRE promoter for cI synthesis.

Question 6

Which equation best represents the process of reverse transcription in HIV?

Accepted Answer

$$\mathrm{RNA} \xrightarrow{	ext{reverse transcriptase}} \mathrm{DNA}$$

Question 7

Which HIV gene encodes the polyprotein that is cleaved into matrix, capsid, nucleocapsid, and p6 proteins?

Accepted Answer

gag

Question 8

A mutation in the cro gene of phage lambda that prevents its expression would most likely result in:

Accepted Answer

Inability to enter the lytic cycle, favoring lysogeny

Question 9

Which protein is responsible for excising phage lambda DNA from the E. coli chromosome to initiate the lytic cycle?

Accepted Answer

Excisionase (xis)

Question 10

In the HIV reproductive cycle, what triggers activation of the provirus after latency?

Accepted Answer

NF-kB transcription factor produced by T cells upon antigen stimulation

Question 11

Which of the following best describes the function of the ESCRT pathway during HIV budding?

Accepted Answer

Facilitates the release of the immature virus particle from the host cell by breaking the neck of the bud

Question 12

If a mutation prevents the lambda repressor (cI) from binding to the OR operator, what is the most likely outcome?

Accepted Answer

The lytic cycle will be favored, as lytic genes are no longer repressed.

Question 13

Which equation represents the integration of phage lambda DNA into the E. coli chromosome?

Accepted Answer

$$	ext{Phage DNA} + 	ext{Host DNA} \xrightarrow{	ext{integrase}} 	ext{Prophage}$$

Question 14

Which HIV protein is responsible for cleaving Gag and Gag-pol polyproteins during viral maturation?

Accepted Answer

HIV protease

Question 15

A patient infected with HIV is found to have a mutation in the env gene. Which viral component is most likely affected?

Accepted Answer

Spike glycoproteins gp120 and gp41

Question 16

Which scenario would most likely induce the lytic cycle in a lysogenic E. coli cell carrying lambda phage?

Accepted Answer

Exposure to UV light, activating RecA protease and degrading the lambda repressor

Question 17

Which of the following is TRUE regarding the host range of viruses?

Accepted Answer

It is determined by the ability of the virus to attach to specific host cell surface proteins.

Question 18

Which equation best represents the process of gap repair synthesis during HIV DNA integration?

Accepted Answer

$$	ext{HIV DNA} + 	ext{Host DNA} \xrightarrow{	ext{DNA polymerase + ligase}} 	ext{Integrated provirus}$$

Question 19

Which of the following best explains why the lysogenic cycle is favored under nutrient-poor conditions?

Accepted Answer

There are insufficient resources for viral replication, so latency allows the virus to persist until conditions improve.

Genetics of Viruses: Structure, Reproductive Cycles, and Regulation (Chapter 18 Study Notes)

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