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Exam 13: Viruses, Viroids and Prions

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Question 71

Multiple Choice

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The phenomenon responsible for the ability of Corynebacterium diphtherium to produce the virulent toxin responsible for the devastating effects of diphtheria is called

A) self-assembly.
B) matrix conversion.
C) prion protein.
D) lysogenic conversion.

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Question 72

Multiple Choice

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You add an unknown phage to a mixture of F⁺ and F^- cells of E. coli and plate out the bacteria. The bacterial colonies that grow are all F^-. How can you explain this phenomenon?

A) The phage bound to a receptor on the sex pilus, and therefore only infected the F⁺ cells (leaving the F^- cells alone) .
B) The phage bound to a receptor on the F^- cells, leaving only them alive and allowing the F⁺ cells to die off.
C) The phage integrated (lysogenized) the F^- cells, giving them a selective advantage over the F⁺ cells.
D) F⁺ cells are uniquely susceptible to phage attack for unknown reasons.

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Question 73

Multiple Choice

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Normal tissue taken from animals and prepared immediately as media for viral growth is termed a(n)

If the infecting phage lacks some critical pieces of DNA necessary for replication it is called

Plant viruses may be passed from generation to generation of an insect vector.

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.

The common species name of the virus is based on the

Electron microscopy is useful for counting viruses and distinguishing between infective and non-infective virions.

A lysogenic cell contains viral DNA, a prophage, integrated into the host chromosome.

Viruses are commonly referred to by their _________ name.

Specialized transduction

Why is it not surprising that AIDS patients frequently suffer a viral-induced tumor? A.HIV genomes integrate into the host cell chromosome.This integration might result in loss of control of the cell cycle (also known as cancer). B.The immune system's CD4⁺ T cells are directly responsible for elimination of tumor cells.HIV attacks them and eliminates them, making a person more susceptible to cancer. C.The therapies for HIV are highly mutagenic, which may lead to cancerous states in people taking the drug regimen. D.Products of an active HIV infection are highly mutagenic-so, as a person's illness progresses, these mutagenic compounds build up and are more capable of inducing a cancerous state.

Using phages to treat a bacterial infection is an interesting idea because

All single-stranded DNA phages are extruded.

The RNA phages contain only a single positive-sense strand of RNA.

Plant viruses enter the host plant via

The host range of a virus depends on the presence of host receptor molecules.

Bacteria infected with filamentous phages are termed