Bio - Chapter 19: Viruses

Viruses can vary with respect to all of the following characteristics EXCEPT

the presence or absence of 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?

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

Components of a virus

Proteins, single-stranded (ss) RNA, double-stranded (ds) DNA, phospholipid bilayer

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

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

Which of the following can't a virus do without a host cell?

Transcribe DNA, produce nucleotides for use in replication and transcription, produce ATP for energy, synthesize proteins.

When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm?

only the nucleic acid

The phage reproductive cycle that kills the bacterial host cell is a __________ cycle, and a phage that always reproduces this way is a __________ phage.

lytic ... virulent

During the lytic...

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In the lytic life cycle of phages

the cell typically dies, releasing many copies of the virus.

Restriction enzymes help defend bacteria against viral infections by

cutting viral DNA once it has entered the cell

A prophage is a

viral genome that has been incorporated into a bacterial cell's chromosome

A phage that inserts itself into the host DNA is called

lysogenic

In the lysogenic cycle of phages...

the phage DNA enters the host cell, forms a circle, and is then incorporated into the host chromosome as a prophage. The prophage replicates with each round of host replication. Under certain conditions, the prophage exits the host chromosome and enters the lytic cycle.

What is the origin of the phospholipid membrane that envelops many animal viruses?

It is "stolen" from the host cell, but it contains some proteins encoded by the viral genome.

Why can flare-ups of herpesvirus infection recur throughout a person's life?

Herpesvirus can leave its DNA behind as minichromosomes in nerve cell nuclei. Stress can trigger another round of virus production, producing characteristic blisters and sores.

How do retroviruses, such as HIV, differ from other viruses?

They can transcribe a DNA copy from a RNA template.

Reverse transcription, carried out by retroviruses, is the process by which

RNA information is copied into DNA

Comparison of a "regular" RNA virus and an RNA retrovirus?

Both produce protein coats via translation of mRNA.

When comparing DNA and RNA viruses, which mutate more quickly, and why?

RNA viruses, because no proofreading is done on RNA molecules

The symptoms of a viral infection in a person can be caused by:

Toxic viral components, such as envelope proteins, the production of toxins by infected cells, the death of infected cells, the reaction of the individual's immune system to the infection.

Vaccines for viral diseases are __________ and help prevent infection by __________.

harmless derivatives of pathogenic viruses ... stimulating the immune system to mount a defense against the actual pathogen

Emerging viruses can originate from which of the following sources?

Animal viruses, the mutation of existing human viruses, viruses previously confined to small, isolated populations that can now spread due to technological or social changes such as the development of affordable international travel.

What is the function of hemagglutinin in the influenza virus?

Hemagglutinin is the protein that helps the influenza virus attach to host cells.

Birds act as a natural __________ for the influenza __________ virus.

reservoir ... A

Which of the following is an example of vertical transmission of a virus in plants?

An infected plant produces seeds that contain the virus, giving rise to infected progeny.

Plant viruses spread throughout the plant by way of

plasmodesmata

Circular RNA molecules that function like a virus in plants are termed

viroid

Prions are __________ that are thought to cause disease by __________.

abnormally shaped proteins ... inducing similar but normally shaped proteins in the brain to adopt the abnormal form

A new pathogenic form of influenza A can emerge when

A mutation occurs in a virus as it passes from one host to another, a virus with a novel genetic makeup recombines with viruses that circulate widely among humans, there is a concurrent infection of a pig or bird by two or more different strains of influenza A, the genomes of two or more influenza A strains mix and match during viral assembly within a host.

The avian flu virus H5N1 is considered a greater long-term threat than the swine flu virus H1N1 because

it has a significantly higher mortality rate