Biology Chapter 19

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Viruses can vary with respect to all of the following characteristics except _____. ( Overview) Your Answer:| the presence or absence of a membranous envelope | | Correct Answer:| the presence or absence of metabolic machinery | |   No. This is a difference among viruses.

A microbiologist analyzes chemicals obtained from an enveloped RNA virus that infects monkeys. He finds that the viral envelope contains a protein characteristic of monkey cells. Which of the following is the most likely explanation? ( Concept 19.1) Your Answer:| Its presence is a result of the monkey's immunological response. | | Correct Answer:| The viral envelope forms as the virus leaves the host cell. | |   No. This does not explain the presence of either the envelope or the monkey protein found on the envelope.

Which of the following, if any, may be a component of a virus? ( Concept 19.1) Your Answer:| single-stranded (ss) RNA | |
Correct Answer:| All of the listed responses are correct. | |   No. Single-stranded RNA is the genetic material of certain viruses, but there is a better answer.

Viruses that infect bacteria are called _____. ( Concept 19.1) Your Answer:| capsomeres | |
Correct Answer:| bacteriophages | |
  No. Capsomeres are the protein subunits of the capsid, the protein shell that encloses the viral genome.

HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because _____. ( Concept 19.2) Your Answer:| other cells produce toxins that destroy the virus before infection can take place | | Correct Answer:| the virus binds to specific receptors that are only present on certain immune cells | |   No. This is not true.

Cancer cells often have protein receptor molecules on their surfaces that differ from those on normal body cells. Given this fact, how might viruses be used to treat cancer? ( Concept 19.2) Your Answer:| Viruses could be engineered to infect only cancer cells by altering viral surface proteins to recognize only the receptors on cancer cells. |   Correct. The host specificity of viruses could be used to make cancer cells "sick" whereas normal body cells would not be infected. This approach would reduce the collateral damage seen in chemotherapy.

Why are phages useful in treating bacterial infections in humans? ( Concept 19.2) Your Answer:| Because of their host specificity, they only attack bacteria. They do not affect eukaryotic cells. | | Correct Answer:| The first three answers are correct. | |   No. This is true, but there is a better answer.

Which of the following can a virus do without a host cell? ( Concept 19.2) Your Answer:| transcribe DNA | |
Correct Answer:| None of the listed responses is correct. | |   No. DNA viruses use the RNA polymerase of the host to transcribe viral DNA.

When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm? ( Concept 19.2) Your Answer:| the tail fibers | |
Correct Answer:| only the nucleic acid | |
  No. The tail remains outside the host cell.

The phage reproductive cycle that kills the bacterial host cell is a _____ cycle, and a phage that always reproduces this way is a _____ phage. ( Concept 19.2) Your Answer:| lysogenic ... virulent | |

Correct Answer:| lytic ... virulent | |
  No. A virus with a lysogenic cycle is a temperate virus.

In the lytic life cycle of phages _____. ( Concept 19.2)
Your Answer:| the viral capsid is assembled according to the genetic information of the bacterium | | Correct Answer:| the cell typically dies, releasing many copies of the virus | |   No. The viral capsid assembles spontaneously from its subunits, the capsomeres.

Restriction enzymes help defend bacteria against viral infections by _____. ( Concept 19.2) Your Answer:| cutting viral DNA once it has entered the cell |   Correct. Restriction...
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