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Exam 13: Viruses, Viroids and Prions

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Question 61

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Why do animal viruses have envelopes and phages rarely do?

A) Since bacteria don't have cell membranes, the bacterial viruses (phages) don't pick them up when they leave the target cells.
B) Phages acquire an outer surrounding that is a part of the cell wall of the bacterium they were created in, rather than an outer surrounding of plasma membrane.
C) Animal viruses will often utilize the envelope in order to fuse with the plasma membrane of a new target cell, gaining entry into the cytoplasm.
D) Animal viruses build the envelope inside of the target cell as they are being replicated, but before the cell breaks open and releases them into the extracellular environment.The envelope is a remnant of this building process.

E) A) and D)
F) A) and C)

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Question 62

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What is a defective phage?

A) A virus that has lost some of its genetic material, and therefore cannot infect a new target cell.
B) A virus that has lost some of its genetic material, and therefore cannot replicate within a new target cell.
C) A virus that lacks the ability to replicate independently of its host cell.
D) A virus that cannot attach to its host cell.

E) A) and B)
F) A) and C)

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Question 63

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The shape of the virus is determined by its

Why is it virtually impossible to stamp out a disease caused by a zoonotic virus?

There are _______ families of DNA containing viruses that infect vertebrates.

What are two ways that phage can replicate in harmony (not directly lysing) their host cell?

Why are viroids resistant to nucleases? A.Having a circular RNA 'genome,' they are resistant to the digestion of most exonucleases (that nibble/digest the free ends of RNA or DNA). B.Having a circular RNA 'genome,' with no protein shell, they are resistant to the protein-degrading activities of nucleases. C.Nucleases will only digest DNA, not RNA-so viroids are protected. D.Viroids have only been identified in plants.Plant nucleases cannot digest RNA.

Capsids are made of a number of capsomeres which are covalently bonded to one another.

The family to which the Rhinovirus belongs is the

Genetic exchange in segmented viruses that allows a zoonotic virus to infect humans is termed

An infection in which the virus is continually present in the body is referred to as

Filamentous virus is incapable of causing a lytic infection.

Virulent as well as temperate phages can serve as generalized transducing phages.

Viruses that infect bacteria are referred to as

Is antigenic shift alone likely to lead to influenza pandemics?

Explain why HIV becomes resistant so quickly when a single drug is used therapeutically. A.The virus is an RNA genome virus-by using host RNA polymerase to directly copy the genome to make more virus particles, there's no proofreading capability.This leads to a high rate of mutation of the viral genome and increased chance for drug resistance. B.HIV utilizes reverse transcriptase to make a cDNA version of its RNA genome.This polymerase is 'sloppy,' with a high rate of error and lack of a proofreading capability.This leads to a high rate of mutation of the viral genome and increased chance for drug resistance. C.HIV synthesizes a protein enzyme that directly cleaves anti-HIV drugs, giving it a characteristically high rate of resistance to a single drug type. D.HIV is constantly changing its genetic structure by swapping genetic elements with other virus strains.This leads to a high rate of mutation of the viral genome and increased chance for drug resistance.

The correct order for the stages of a phage infection is:

Would ID₅₀ and LD₅₀ necessarily be the same for a given virus? Why or why not? A.Yes, because the number of viruses that infect 50% of a test population should also kill 50% of that test population. B.No, because a virus may be highly infectious (very low ID₅₀ value) but only marginally lethal (very high LD₅₀ value).A prime example of this is the rhinovirus (common cold virus). C.No, because very few viruses are lethal, yet many are highly infectious.The 2 values should ALWAYS be different. D.Yes, because what we're actually describing here is infection/killing of individual CELLS, not of entire organisms.If a cell is infected, it will always be killed.

In the region of budding, the plasma membrane becomes involved with

What part of the attached bacteriophage enters through the host cell wall?