Q: Which equation best represents the replication of a positive-sense ssRNA virus genome?

$$\text{Positive-sense ssRNA} \xrightarrow{\text{RdRp}} \text{Negative-sense ssRNA} \xrightarrow{\text{RdRp}} \text{Positive-sense ssRNA}$$

Q: Which equation best represents the replicative cycle of a retrovirus?

$$\text{ssRNA} \xrightarrow{\text{Reverse transcriptase}} \text{dsDNA} \xrightarrow{\text{Integrase}} \text{Host genome} \xrightarrow{\text{RNA polymerase II}} \text{mRNA/ssRNA}$$

Question 1

Which of the following statements best explains why viruses are not considered living organisms?

Accepted Answer

Viruses lack cellular structure and cannot reproduce or metabolize outside a host cell.

Question 2

A scientist passes sap from a diseased tobacco plant through a filter that traps bacteria, then rubs the filtrate on healthy plants. The healthy plants become diseased. What does this experiment demonstrate?

Accepted Answer

The disease is caused by a non-cellular infectious particle, likely a virus.

Question 3

Which feature distinguishes a positive-sense single-stranded RNA virus from a negative-sense single-stranded RNA virus?

Accepted Answer

Positive-sense RNA viruses can be directly translated by host ribosomes.

Question 4

Which equation best represents the replication of a positive-sense ssRNA virus genome?

Accepted Answer

$$	ext{Positive-sense ssRNA} \xrightarrow{	ext{RdRp}} 	ext{Negative-sense ssRNA} \xrightarrow{	ext{RdRp}} 	ext{Positive-sense ssRNA}$$

Question 5

During the lytic cycle of a bacteriophage, what is the fate of the host cell?

Accepted Answer

The host cell is lysed, releasing new phage particles.

Question 6

Which mechanism allows bacteria to recognize and destroy foreign phage DNA while protecting their own DNA?

Accepted Answer

Restriction-modification system

Question 7

How does the CRISPR-Cas system provide adaptive immunity to bacteria?

Accepted Answer

By using short RNA guides to direct Cas proteins to cut complementary phage DNA.

Question 8

Which of the following is conceptually similar to the CRISPR-Cas system in terms of mechanism?

Accepted Answer

RNA interference (RNAi) in eukaryotes

Question 9

A retrovirus like HIV uses which enzyme to convert its RNA genome into DNA?

Accepted Answer

Reverse transcriptase

Question 10

Which equation best represents the replicative cycle of a retrovirus?

Accepted Answer

$$	ext{ssRNA} \xrightarrow{	ext{Reverse transcriptase}} 	ext{dsDNA} \xrightarrow{	ext{Integrase}} 	ext{Host genome} \xrightarrow{	ext{RNA polymerase II}} 	ext{mRNA/ssRNA}$$

Question 11

Which protein is the primary target for SARS-CoV-2 vaccines?

Accepted Answer

Spike (S) protein

Question 12

Why are RNA viruses more likely to be associated with emerging viral diseases?

Accepted Answer

RNA viruses have an unusually high rate of mutation, allowing rapid adaptation.

Question 13

Which of the following best describes the function of viral glycoproteins in animal viruses?

Accepted Answer

They bind to specific receptor molecules on the surface of host cells.

Question 14

Which of the following is NOT a plausible outcome of the lysogenic cycle in bacteriophages?

Accepted Answer

The host cell is immediately lysed upon phage DNA entry.

Question 15

Which of the following best explains why antibiotics are ineffective against viral infections?

Accepted Answer

Viruses lack the cellular structures targeted by antibiotics.

Question 16

Which process is used by eukaryotic cells to defend against viral infection by targeting viral RNA for degradation?

Accepted Answer

RNA interference (RNAi)

Question 17

Which equation best represents the action of RNA interference in eukaryotic cells?

Accepted Answer

$$	ext{dsRNA} \xrightarrow{	ext{Dicer}} 	ext{siRNA} \xrightarrow{	ext{RISC}} 	ext{Target viral RNA degradation}$$

Question 18

Which of the following is a key difference between a provirus and a prophage?

Accepted Answer

A provirus remains permanently integrated in the host genome, while a prophage can exit and re-enter the lytic cycle.

Question 19

Which of the following best describes a pandemic?

Accepted Answer

A global epidemic of an infectious disease.

Lecture 21 (Unit 2) - Viruses: Structure, Replication, and Host Defenses

Guida di studio - Domande di pratica

Study guide - Flashcard