chapter 19

Both produce protein coats via translation of mRNA

"regular" RNA virus and an RNA retrovirus

is wrapped in host plasma membrane or nuclear membrane (which contains host proteins)

An enveloped virus

is a difference among viruses and is used for classification

DNA or RNA as the genetic material

have lower mutation rates because the host cell's proofreading enzymes correct most of the errors in the virus's DNA genome.

DNA viruses

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

Emerging viruses can originate from

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.

only a small number of the viral genes are expressed the viral nucleic acid is replicated along with the host DNA the viral nucleic acid inserts itself into the host chromosome the nucleic acid core of the phage is all that enters the host cell

In the lysogenic cycle of phages

the cell typically dies, releasing many copies of the virus

In the lytic life cycle of phages

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. and then altered with the addition of viral components.

are proteins.

Prions

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

RNA information is copied into DNA

mutate more quickly because no proofreading is done on RNA molecules

RNA viruses

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have

T4 protein and T4 DNA.

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.

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

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

They can transcribe a DNA copy from a RNA template.

are directed against the virus itself.

Vaccines for viral diseases

only infect specific cells based on the "lock-and-key" fit between viral surface proteins and cell surface receptors many do not infect humans because human cells do not have the right receptors cannot synthesize any of the enzymes necessary to carry out metabolism

Viruses

DNA or RNA as the genetic material the type of host cell it can infect the presence or absence of a membranous envelope single- or double-stranded nucleic acids

Viruses characteristics

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?

Viruses could be engineered to infect only cancer cells by altering viral surface proteins to recognize only the receptors on cancer cells.

Because of their host specificity, they only attack bacteria. They do not affect eukaryotic cells. Because of their specificity, a phage can be used that will only infect the pathogenic bacteria, leaving helpful bacteria alone. Because phages are free to evolve, bacteria are less likely to develop a lasting resistance to them.

Why are phages useful in treating bacterial infections in humans?

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 Correct. The abnormally shaped proteins are thought to clump together, causing microscopic holes in the brain that are ultimately fatal.

contain nucleic acids that code for proteins.

all viruses.

A virus that infects bacteria; also called a phage.

bacteriophages

Viruses that infect bacteria are called _____.

bacteriophages

To cause a human pandemic, the H5N1 avian flu virus would have to

become capable of human-to-human transmission.

The protein shell that encloses a viral genome. It may be rod-shaped, polyhedral, or more complex in shape.

capsid

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

component of a virus

Restriction enzymes help defend bacteria against viral infections by _____

cutting viral DNA once it has entered the cell

The herpesvirus becomes a prophage during the lysogenic cycle of the infection, so the viral genome is recombined with the host DNA.

description of how a virus acts during infection of a bacterium

A general outbreak of a disease.

epidemic

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

function of hemagglutinin in the influenza virus

is common to both bacteria and viruses?

genetic material composed of nucleic acid

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

RNA viruses require their own supply of certain enzymes because

host cells lack enzymes that can replicate the viral genome

The limited number of species whose cells can be infected by a particular virus.

host range

Older people were likely exposed to earlier H1N1 viruses that primed their immune systems for the virus of the 2009 pandemic. The hypothesis pertains to immunity differences between the young and old age groups

hypothesis for the surprisingly low infection and mortality rate among people over 64 years of age during the 2009 H1N1 pandemic

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

A phage that inserts itself into the host DNA

lysogenic

A type of phage replicative cycle in which the viral genome becomes incorporated into the bacterial host chromosome as a prophage, is replicated along with the chromosome, and does not kill the host.

lysogenic cycle

does not kill the bacterial host cell virus in the cycle can be induced into a lytic cycle, which can lead to host cell lysis

lysogenic cycle

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

A type of phage replicative cycle resulting in the release of new phages by lysis (and death) of the host cell.

lytic cycle

Emerging viruses arise by

mutation of existing viruses. the spread of existing viruses to new host species. the spread of existing viruses more widely within their host species.

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 a virus with a novel genetic makeup recombines with viruses that circulate widely among humans a mutation occurs in a virus as it passes from one host to another

new pathogenic form of influenza A can emerge

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

only the nucleic acid Portions of the virus remain outside the host cell.

A virus that infects bacteria; also called a bacteriophage.

phage

Plant viruses spread throughout the plant by connect the cytoplasm of different cells and allow nutrients and fluids to move throughout the plant. Viruses can spread through these connections.

plasmodesmata

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

prophage

Birds act as a natural _____ for the influenza _____ virus

reservoir ... A

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).

restriction enzyme

refers to RNA viruses of animals that transcribe their RNA into DNA when they infect a host. This DNA can then be incorporated into the host cell's DNA as a provirus.

retrovirus

are a type of RNA virus.

retroviruses

can be caused by: the production of toxins by infected cells toxic viral components, such as envelope proteins the death of infected cells the reaction of the individual's immune system to the infection

symptoms of a viral infection in a person

A phage that is capable of replicating by either a lytic or lysogenic cycle.

temperate phage

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

RNA information is "read" to form a protein molecule

translation.

An infected plant produces seeds that contain the virus, giving rise to infected progeny. Correct. Vertical transmission refers to the spread of a virus from parent to offspring.

vertical transmission of a virus in plants?

Circular RNA molecules that function like a virus in plants

viroid

An infectious particle incapable of replicating outside of a cell, consisting of an RNA or DNA genome surrounded by a protein coat (capsid) and, for some viruses, a membranous envelope.

virus

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.

AIDS (acquired immunodeficiency syndrome)

bypasses DNA.

A regular RNA virus

is an animal virus, whereas a prophage is the integration of bacteriophage genome into a bacterial chromosome.

H5N1

The infectious agent that causes AIDS. HIV is a retrovirus.

HIV (human immunodeficiency virus)

is replicated by the host cell's metabolic machinery.

Phage DNA