Chapter 19 Mastering Biology

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

only the nucleic acid

Which of the following is not a class I virus? -adenovirus -parvovirus -polyomavirus -papillomavirus -herpesvirus -poxvirus

parvovirus

All of the following types of viruses have envelopes except __________.

picornovirus

Candidates for the original source of viral genomes include __________.

plasmids and transposons

Viruses can vary with respect to all of the following characteristics except __________. -the presence or absence of metabolic machinery -the type of host cell it can infect -single-or double-stranded nucleic acids -DNA or RNA as the genetic material -presence or absence of a membranous envelope

presence or absence of metabolic machinery

Viral DNA incorporated into a bacterial chromosome is known as a(n) __________.

prophage

Some viruses have membranous envelopes. Where do viral envelopes typically originate from?

Membranes from the host cell

Animals that harbor and can transmit a particular virus but are generally unaffected by it are said to act as a __________ for that virus.

Natural reservoir

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

RNA information is copied into DNA

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

RNA viruses, because no proofreading is done on RNA molecules

Which of the following statements correctly describes one difference between virulent phages and temperate phages?

Virulent phages replicate only through the lytic cycle, and temperate phages replicate using both the lytic and the lysogenic cycles

Why are viruses often considered to be nonliving?

Viruses do not carry out metabolic processes, a primary characteristic of living organisms

A widespread outbreak of a viral disease is called a(n) __________, and a global outbreak is called a(n) __________.

epidemic; pandemic

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

Class IV viruses are characterized by which of the following types of genomes?

single-stranded RNA that serves as mRNA

How are retroviruses different from other types of viruses?

they use the enzyme reverse transcriptase to transcribe a copy of DNA from their own RNA

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

Viroids

Which of the following is an example of vertical transmission of a virus in plants? -two neighboring plants touch each other, allowing viruses present in one plant to infect the other -viral particles are carried by the wind from one plant to another -all of the listed are correct -viral particles are carried from one plant to another by a pair of pruning shears -an infected plant produces seeds that contain the virus, giving rise to infected progency

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

Genomes of viruses may consist of which of the following types of nucleic acids?

Double/single stranded DNA Double/single stranded RNA

How does a retrovirus like HIV enter a host cell?

Glycoproteins on the viral envelope bind to receptors on the host cell. The viral envelope fuses with the host cell's plasma membrane, facilitating uptake of the virus by the host cell.

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

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

Which of the following events occurs during the lytic life cycle of phages?

The host cell usually dies, releasing many new copies of the virus

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

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

Viruses that infect bacteria are called __________.

bacteriophages

How do prions propagate and replicate themselves?

convert normal proteins into the misfiled prion version

Restriction enzymes help defend bacteria against viral infections by __________.

cutting viral DNA once it has entered the cell

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 is called __________.

lysogenic

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