Chapter 5 Review

Viruses in the extracellular state possess

few, if any, active enzymes.

Which is not true of viruses?

They infect animal and plant cells only.

Which of the following is true of viruses in the extracellular phase?

They behave as a macromolecular complex and are no more alive than are ribosomes.

A complete virus particle is called a

virion

The nucleic acids carried by viruses usually consist of

either DNA or RNA

Which of the following is not true of viruses?

Viruses replicate by binary fission.

One way in which small viruses package more information into a very small genome is to use

overlapping genes so that the same base sequence is read in more than one reading frame.

Almost all known plant viruses are

RNA viruses

Virus morphology does not include which of the following characteristics?

host range

Peplomers

are glycoprotein spikes protruding from the outer surface of the viral envelope.

Icosahedral viruses are constructed from ring- or knob-shaped units called

capsomers

Viruses that are polyhedrons with 20 sides are said to have what type of symmetry.

icosahedral

The most common capsid morphologies are

icosahedral and helical.

The largest viruses known are the

poxviruses

The simplest viruses consist of

RNA or DNA in a protein coat

Viral capsid protein subunits are called

protomers

In an enveloped virus, the part of the virus including the nucleic acid genome and the surrounding protein coat but not the envelope is called the

nucleocapsid

Some complex viruses have icosahedral symmetry in the head region and helical symmetry in the tail. Overall, these viruses are said to have what type of symmetry.

binal

Glycoprotein spikes protruding from the outer surface of viral envelopes function as

factors that bind to host cells

segmented genome

exists as several separate, nonidentical molecules that may be packaged together or separately.

Many of the enzymes found in virus particles are

involved in the replication of viral nucleic acid.

Which of the following is/are not true about viral envelopes?

They are typical lipid monolayers with embedded viral proteins.

Viral envelopes are composed of

proteins lipids carbohydrates

Two major types of symmetry found in viruses include

icosahedral and helical

The function of the viral protein coat is to

protect the viral genetic material and aid in the transfer of the viral genetic material between host cells.

The protein coat surrounding the viral genome is called the

capsid

Which of the following is most true of a viral DNA genome?

It may have the normal bases found in prokaryotic and eukaryotic DNA, or it may have one or more unusual bases.

Virion size ranges from

10-400 nm.

Viral capsids are generally constructed without any outside aid once the subunits have been synthesized. This process is called

self-assembly

In which of the following stages of the viral infectious cycle do enveloped viruses usually acquire their envelopes?

release

Most enveloped viruses use the host

plasma membrane as their envelope source.

Poliovirus receptors are found

in nasopharynx, gut, and spinal cord anterior horn cells

Nonenveloped viruses most often gain access to eukaryotic host cells by

endocytosis

Human cancer causing viruses most often have a ___________ genome.

dsDNA

Adult T-cell leukemia is thought to be caused by

retroviruses

Genes whose expression (or abnormal expression) causes cancer are called

oncogenes

Which of the following has been associated with a form of liver cancer?

hepatitis B virus (Answer)

Microscopic or macroscopic degenerative changes or abnormalities in infected host cells and tissues are called

cytopathic effects

Animal viruses have been cultivated in

suitable host animals embryonated eggs tissue cultures (monolayers of animal cells)

Which of the following can be used to cultivate plant viruses?

cultures of separated plant cells whole plants plant protoplast cultures

2 mls of a 10^-4 dilution of a virus preparation yields 90 plaques. What is the number of PFU per ml in the undiluted virus preparation?

4.5 10^6

A ________ assay is most useful for determining the viability of a viral preparation?

plaque

Hemagglutination is

the clumping together of red blood cells in the presence of a viral suspension.

Localized areas of destruction occurring on plants that have been infected by a virus are referred to as __________ lesions.

necrotic

Which of the following is not a mechanism by which viruses cause cancer?

They produce defective interfering particles.

Which of the following is not true regarding the human hepatitis D virusoid?

Its genome is a circular, single-stranded RNA molecule It needs a helper virus to infect host cells. It produces one protein called the delta antigen.

Which of the following is not true of viroids?

Extracellular viroids have a lipid bilayer envelope.

Viroids are of economic significance because they cause disease in

plants

Viroids are:

short infectious single stranded RNAs that can infect some plants.

Prions are of significance because they cause infections of

domestic animals and humans.

Which of the following diseases is (are) caused by prions?

scrapie mad cow disease kuru and Creutzfeldt-Jakob Disease