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50 Cards in this Set

  • Front
  • Back
AIDS (acquired immunodeficiency syndrome)
The symptoms and signs present during the late stages of HIV infection, defined by a specified reduction in the number of T cells and the appearance of characteristic secondary infections.
A virus that infects bacteria
The protein shell that encloses a viral genome. It may be rod-shaped, polyhedral, or more complex in shape.
HIV (human immunodeficiency virus)
The infectious agent that causes AIDS. HIV is a retrovirus.
host range
The limited range of host cells that each type of virus can infect.
lysogenic cycle
A type of phage reproductive cycle in which the viral genome becomes incorporated into the bacterial host chromosome as a prophage and does not kill the host.
lytic cycle
A type of phage reproductive cycle resulting in the release of new phages by lysis (and death) of the host cell.
A global epidemic.
A virus that infects bacteria
An infectious agent that is a misfolded version of a normal cellular protein. Prions appear to increase in number by converting correctly folded versions of the protein to more prions.
A phage genome that has been inserted into a specific site on a bacterial chromosome.
A viral genome that is permanently inserted into a host genome.
restriction enzyme
An endonuclease (type of enzyme) that recognizes and cuts DNA molecules foreign to a bacterium (such as phage genomes). The enzyme cuts at specific nucleotide sequences (restriction sites).
An RNA virus that reproduces by transcribing its RNA into DNA and then inserting the DNA into a cellular chromosome
reverse transcriptase
An enzyme encoded by certain viruses (retroviruses) that uses RNA as a template for DNA synthesis.
temperate phage
A phage that is capable of reproducing by either a lytic or lysogenic cycle.
See immunization.
A harmless variant or derivative of a pathogen that stimulates a host’s immune system to mount defenses against the pathogen.
viral envelope
A membrane that cloaks the capsid that in turn encloses a viral genome.
A plant pathogen consisting of a molecule of naked, circular RNA a few hundred nucleotides long.
virulent phage
A phage that reproduces only by a lytic cycle.
Viruses are smaller and simpler than some bacteria and other prokaryotes
lacking the structures and metabolic machinery found in cells, most viruses are little more than genes packaged in protein coats.
Latin root for the word virus means
“poison” because they are capable of causing a wide variety of diseases and can be spread between organisms.
Viruses cannot reproduce or carry out metabolic activities outside of a
host cell.
Simple phrase used by two researchers describes viruses aptly enough
Viruses lead “a kind of borrowed life.”
Molecular biology was born in the laboratories of biologists studying viruses that infect
Experiments with viruses provided important evidence that
genes are made of nucleic acids, and they were critical in working out the molecular mechanisms of the fundamental processes of DNA replication, transcription, and translation.
The study of viruses has led to the development of techniques that enable scientists to manipulate
genes and transfer them from one organism to another.
Viruses are used as
agents of gene transfer in gene therapy.
Tobacco Mosaic Disease
stunts the growth of tobacco plants and gives theirs a mottled, or mosaic, coloration.
1883, Adolf Mayer, discovered
that he could transmit the disease from plant to plant by rubbing sap extracted from diseased leaves onto healthy plants, searched for the infectious microbe in the sap, suggested that the disease was cause by unusually small bacteria that were invisible under a microscope.
Ivanowsky tested Mayer’s hypothesis, using a filter designed to remove
bacteria, after filtration, the sap still produced mosaic disease, clung to the hypothesis that bacteria were small enough to pass through the filter or made a toxin that could do so.
Ivanowsky’s second possibility was rule out by Beijerinck who carried out a series of experiments that showed that the infectious agent in the filtered sap could reproduce
in fact, the pathogen reproduced only within the host it infected, showing that unlike bacteria used in the lab at that time the mysterious agent of mosaic disease could not be cultivated on nutrient media test tubes or petri dishes.
Beijerinck imagined a reproducing particle must smaller and simpler than a bacterium
generally credited with being the first scientist to voice the concept of a virus.
Beijerinck’s suspicions were confirmed in 1935 by
Stanley who crystallized the infectious particle, now known as tobacco mosaic virus (TMV), now seen with the help of an electron microscope.
Tiniest viruses re only
20 nm in diameter – smaller than a ribosome, millions could easily fit on a pinhead.
Largest know virus
diameter of several hundred nanometers is barely visible in the light microscope.
Examining the structure of viruses more closely reveals that they are
infectious particles consisting of nucleic acid enclosed in a protein coat and, in some case, a membranous envelope.
Viruses can vary with respect to all of the following characteristics except _____. ( Concept 19.1)
Your Answer:

the presence or absence of metabolic machinery

Correct. Viruses are not classified by the presence or absence of metabolic machinery, because viruses do not contain metabolic machinery.
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:

The virus fools its host by mimicking its proteins.

Correct Answer:

The viral envelope forms as the virus leaves the host cell.

No. Although this may be true, it is not an explanation of how the virus acquired the protein.
Which of the following, if any, may be a component of a virus? ( Concept 19.1)
Your Answer:

all of the above
Correct. Viral genomes may consist of double-stranded or single-stranded DNA, double-stranded or single-stranded RNA, and many contain an envelope made up of a phospholipid bilayer.
Viruses that infect bacteria are called _____. ( Concept 19.1)
Your Answer:


Correct. Viruses that infect bacteria are called bacteriophages or, simply, phages.
HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because _____. ( Concept 19.2)
Your Answer:

the virus binds to specific receptors that are only present on certain immune cells

Correct. The virus binds to receptors such as CD4 that are only present on certain cells such as helper T cells.
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" while 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:

The first three answers are correct.

Correct. Phage therapy is useful because of its host specificity and ability to evolve to avoid the problems of resistance.
Which of the following can a virus do without a host cell? ( Concept 19.2)
Your Answer:

none of the above

Correct. Viruses are obligate intracellular parasites. They require a host cell to carry out all of the above cellular processes (and more).
When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm? ( Concept 19.2)
Your Answer:

only the nucleic acid

Correct. After attaching to receptors on the surface of the bacterial cell, the virus injects its DNA into the 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:

lytic; virulent

Correct. A lytic cycle ends with the lysis of the bacterial host cell.
In the lytic life cycle of phages _____. ( Concept 19.2)
Your Answer:

the cell typically dies, releasing many copies of the virus

Correct. After attaching to receptors on the surface of the bacterial cell, the phage injects its nucleic acid into the cell. The phage then hijacks the cellular machinery to manufacture many copies of itself.
A phage that inserts itself into the host DNA is called _____. ( Concept 19.2)
Your Answer:

a bacteriophage

Correct Answer:


No. "Bacteriophage" and "phage" are synonyms.