Micro Chapter 5

A(n) _______ is the protein shell around the nucleic acid core of a virus.

Capsid

Virus capsids are made from subunits called _

Capsomeres

Viruses are ultramicroscopic because they range in size from 2 mm to 450 mm.

False (nm)

Viruses attach to their hosts via _

Host glycoproteins

List some cytopathic effects:

Inclusions in the nucleus or cytoplasm; Cells change shape; Multinucleated giant cells

The envelope of enveloped viruses __

Is obtained by viral budding or exocytosis

In phage replication, _

only the phage nucleic acid enters the bacterial cell

The core of every virus particle always contains

Either DNA or RNA

The core of every virus particle always contains _

Either DNA or RNA

Glycoprotein spikes facilitate the release of the virus from the host cell.

FALSE

T/F: Viral nucleic acid is made inside the bacterium and is combined with viral protein coat already present outside.

FALSE

A specific animal virus has the ability to attach to and enter almost any animal host cell.

False

Viruses are ultramicroscopic because they range in size from 2 mm to 450 mm.

False

One of the principal capsid shapes is a 20-sided figure with 12 evenly spaced corners referred to as a(n) _______ capsid.

Icosahedral

What cytopathic effect is shown here, and what is the likely causative viral agent?

Syncytium; respiratory syncytial virus

Viruses are the most common cause of acute infections that do not result in hospitalization.

TRUE

What structures are used by bacteriophages to attach to host cell receptors?

Tail fibers

Viruses acquire envelopes around their nucleocapsids during

Release

Involves enzymatic destruction of the capsid

Releases viral nucleic acid into the cell; Occurs before replication

The protein coat of a virus is called the ____

capsid

An ideal antiviral drug would be one that ___

disrupted an integral viral process while causing little damage to the host cell

A fully formed virus that can cause an infection in a host cell is called a virion.

true

Lysogeny refers to __

viral genome inserting into bacterial host chromosome

Viruses have all the following except ___

Definite shape, genes, ability to infect host cells, ultramicroscopic size; DOES NOT HAVE METABOLISM

Uncoating of viral nucleic acid __

Does NOT occurs in bacteriophage multiplication (because it is injected)

An ideal antiviral drug would be one that killed the host cell, effectively preventing the virus from replicating.

False

Host cells of viruses include __

Humans and other animals; plants and fungi; bacteria; protozoa and algae (all correct)

What is the source of enveloped viruses' envelopes?

The host cell's membrane

Viruses are unable to multiply outside of a host cell.

True

Viruses are used to produce vaccines for prevention of certain viral infections.

True

When a virus enters a host cell, the viral genes redirect the genetic and metabolic activities of the host cell.

True

T/F: Viruses cannot be seen in a light microscope

True- only electron microscope due to size

The process of dissolving the envelope and capsid to release the viral nucleic acid is _____

Uncoating

A negative-sense RNA virus _

must synthesize a positive RNA copy of its genome

Which of the following occurs during assembly of an enveloped virus?

A nucleocapsid is formed and viral spikes insert in host cell membrane.

Creutzfeldt-Jacob disease is ___

A spongiform encephalopathy of humans

Helical and icosahedral are terms used to describe the shapes of a virus ______.

Capsid

Which of the following is not associated with every virus?

Envelope; all viruses have: capsomeres, capsid, nucleic acid, genome

Mammalian viruses capable of starting tumors are _

Oncoviruses

The host cells that viruses can infect are determined by the ____

Receptors on the host cell

The protein projections on the surface of a virus that are involved in attachment to the host cell are called

Spikes

Move the steps into the proper order to review the two ways in which animal viruses penetrate host cells.

This question reviews the two ways in which animal viruses penetrate host cells, (1) endocytosis of entire viral particle, or (2) fusion of the viral envelope wih the host cell membrane.

Viral tissue specificities are called _

Tropisms

A fully formed virus that can cause an infection in a host cell is called a virion.

True

Viruses are simple, noncellular, and lack mRNA.

True

In general, most DNA viruses multiply in the host cell's _______, while most RNA viruses multiply in the host cell's _______.

Nucleus; cytoplasm

A viral infection in which the virus can remain latent in the host cell for weeks to years is described as a(n) _________ infection, and may lead to cancer if host DNA is altered.

Persistent

Viruses with _______ -sense RNA contain the correct message for translation, while viruses with _______ -sense RNA must first be converted into a correct message.

Positive; negative

Infectious protein particles are called __

Prions

Viral spikes __

Protrude from the envelope; Not present on all viruses, block attachment between virus and host or derived from host proteins

Choose the statement that best describes the role of viral surface proteins or spikes.

Provide means of attachment to host cell surface

The event that occurs in bacteriophage multiplication that does not occur in animal virus replication is ________.

injection of only the viral nucleic acid into the host cell

The development of antiviral drug therapy is difficult because __

viruses are obligate intracellular parasites so the host cell can be harmed by the drug

The correct order of the stages for phage replication are...(1 = assembly; 2 = attachment;3 = transcription/replication; 4 = release; 5 = penetration)

2, 5, 3, 1, 4

The primary purpose of viral cultivation is __

; Isolate and identify viruses in clinical specimens; To prepare virus for vaccines; To do detailed research on viral structure, lifestyle, genetics and effects on host cells

Rather than to argue that a virus is "alive," it is preferred to say a virus is _______.

Active (and inactive)

All of the following pertain to virus envelopes except ___

Are located between the capsid and nucleic acid; True: Contains special virus proteins; Are comprised primarily of lipids; Gained as a virus leaves the host cell membrane; Help the virus particle attach to the host cell

Viruses that infect bacteria are specifically called ___

Bacteriophages

A common method for cultivating viruses in the lab is to use in vitro systems called _______ cultures.

Cell

Replication of T4 Phage in E. coli -Why are viruses virulent? Viruses require cells to replicate themselves. They are parasites. They are also pathogens, entities that cause disease. Pathogens vary in their virulence, the extent to which they are harmful to their hosts. Pathogens may evolve reduced virulence if their probability of transfer to a new host at any given point in time is low. If a virulent virus had a low probability of reaching a new host, individual viruses that did not seriously harm their host would tend to persist. Highly infectious viruses such as those causing influenza will not tend to evolve reduced virulence. View the animation below, and then complete

In the attachment step of phage replication, _; protein fibers in the phage tail attach to specific receptors on the bacterial cell wall

New, nonenveloped virus release occurs by __

Lysis; (budding and exocytosis would make envelope)

Cells grown in culture form a(n) __

Monolayer

A naked virus has only a(n) __

Nucleocapsid

Cellular inclusions, cell enlargement, cell fusion, cell lysis, and syncytia formation are all examples of cytopathic effects demonstrated by viral-infected cells.

True

It is necessary to culture viruses both in vivo and in vitro so that vaccines can be developed, analysis of viral genomes can be made and viruses in clinical specimens can be identified.

True

Spikes are glycoproteins projecting outward from the surface of some viruses and may be used for attachment to a host cell.

True

Viruses are simple, noncellular, and lack ribosomes.

True

Viruses are unable to multiply outside of a host cell

True

Analyze the statements below, and select those that correctly apply to the unique characteristics of viruses.

Viruses are species specific and infect cells from all five kingdoms- true; while viruses are not considered living because they cannot direct their own multiplication, they are more than simply an aggregate of macromolecules since they can direct the behavior of living cells- true; viruses have a nucleic acid genome; however it may be either DNA or RNA and the nucleic acids may be single or double stranded- true; FALSE- viruses are considered living because they can direct their own multiplications as well as the behavior of living cells; FALSE- some viruses are parasitic, but others carry ribosomes in their capsid allowing them to translate their own proteins

The general steps in a viral multiplication cycle are ________

adsorption, penetration, synthesis, assembly, and release

Which of the following will not support viral cultivation?

(all) live lab animals, embryonated bird eggs, primary cell cultures, continuous cell cultures