Deck 6: Viruses and Other Acellular Infectious Agents

Question 1

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.

Answer 1

True

Question 2

Viruses such as MS2 and Qß pack additional information into their genomes through the use of overlapping genes.

Answer 2

True

Question 3

Almost all known plant viruses are RNA viruses.

Answer 3

True

Question 4

The presence or absence of an envelope is not useful in classifying viruses because any given virus may at one time have an envelope and at another time not have an envelope.

Question 5

The nucleic acids carried by viruses usually consist of

A)DNA.
B)RNA.
C)either DNA or RNA.
D)both DNA and RNA simultaneously.

Question 6

The most common capsid morphologies are icosahedral and helical.

Question 7

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

Question 8

Viral capsid protein subunits are called

A)auxomers.
B)elastomers.
C)protomers.
D)viromers.

Question 9

Virus morphology does not include which of the following characteristics?

A)size
B)shape
C)presence or absence of an envelope
D)host range

Question 10

A complete virus particle is called a

A)capsid.
B)nucleocapsid.
C)virion.
D)cell.

Question 11

Viruses infecting protists,including algae,have never been detected.

Question 12

The largest of the viruses are similar in size to some small bacteria and are large enough to be seen with a light microscope.

Question 13

The simplest viruses consist of

A)RNA only.
B)Protein only.
C)RNA or DNA in a protein coat.
D)RNA or DNA in a protein coat covered with lipid envelope.
E)RNA,DNA and enzymes in a protein coat with a lipid envelope.

Question 14

Which of the following is not true of viruses?

A)Viruses are acellular.
B)Viruses consist of one or more molecules of DNA or RNA enclosed in a coat of protein and sometimes in other more complex layers.
C)Viruses can exist in two phases: intracellular and extracellular.
D)Viruses replicate by binary fission.

Question 15

Viruses that are polyhedrons with 20 sides are said to have __________ symmetry.

Question 16

Which is not true of viruses?

A)They can exist in an intracellular or extracellular phase.
B)They infect animal and plant cells only.
C)They can be observed with an electron microscope.
D)They are acellular.
E)They replicate only inside host cells.

Question 17

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

A)They possess many different enzymes.
B)They can reproduce independently of living cells but only at a slow rate.
C)They behave as a macromolecular complex and are no more alive than are ribosomes.
D)They possess many different enzymes and they can reproduce independently of living cells but only at a slow rate

Question 18

Viruses in the extracellular state possess few,if any,active enzymes.

Question 19

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

Question 20

Viruses have typical cellular structure like other living organisms.

Question 21

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

A)capsid.
B)nucleocapsid.
C)matrix.
D)virion.

Question 22

Enveloped viruses may enter their host cells by fusion of their envelope with the cytoplasmic membrane,thereby depositing their nucleocapsid within the cell.

Question 23

Which of the following represent(s)the way(s)in which enveloped viruses acquire their envelopes?

A)Budding through the plasma membrane.
B)Budding through internal cellular membranes.
C)Viral enzymes are responsible for production of the envelope.
D)For some viruses,a is correct; for other viruses,b is correct.

Question 24

The protein coat surrounding the viral genome is called the

A)capsule.
B)capsid.
C)matrix.
D)envelope.

Question 25

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

A)bilateral
B)binal
C)complex
D)none of these

Question 26

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

A)penetration
B)component biosynthesis
C)assembly
D)release

Question 27

Two major types of symmetry found in viruses include

A)icosahedral and radial.
B)icosahedral and helical.
C)helical and radial.
D)radial and bilateral.

Question 28

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

A)The envelope proteins are virus specific.
B)The envelope lipids and carbohydrates are derived from the host.
C)They are typical lipid monolayers with embedded viral proteins.
D)The envelope proteins are virus specific and the envelope lipids and carbohydrates are derived from the host

Question 29

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

A)diploid
B)segmented
C)polyploid
D)fractionated

Question 30

Virus receptors are often not distributed uniformly over the surface of host cells,but are instead concentrated in lipid rafts.

Question 31

Many of the enzymes found in virus particles are

A)required for viral attachment to host cells.
B)involved in viral entry into host cells.
C)involved in the replication of viral nucleic acid.
D)all of the choices

Question 32

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

A)It uses the same four nitrogenous bases found in prokaryotic and eukaryotic DNA.
B)It may have the normal bases found in prokaryotic and eukaryotic DNA,or it may have one or more unusual bases.
C)It is usually composed of unusual bases unique to viruses.
D)Viruses do not use DNA for their genome.

Question 33

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

A)toxins.
B)factors that bind to host cells.
C)cell lysis factors.
D)factors needed for site specific recombination.

Question 34

Most enveloped viruses use the host __________ membrane as their envelope source.

A)plasma
B)nuclear
C)mitochondrial
D)none of these

Question 35

Viral envelopes are composed of

A)proteins.
B)lipids.
C)carbohydrates.
D)all of the choices

Question 36

The function of the viral protein coat is to

A)protect the viral genetic material.
B)aid in the transfer of the viral genetic material between host cells.
C)elicit the production of protective antibodies.
D)protect the viral genetic material and aid in the transfer of the viral genetic material between host cells.

Question 37

Nonenveloped viruses most often gain access to eukaryotic host cells by

A)fusion with the host cell plasma membrane followed by entrance of the nucleocapsid into the cytoplasm.
B)endocytosis.
C)pinocytosis.
D)nucleic acid injection through the plasma membrane.

Question 38

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

A)facilitated assembly.
B)self-assembly.
C)spontaneous maturation.
D)self-maturation.

Question 39

Virion size ranges from

A)1-40 nm.
B)10-400 nm.
C)600- 1,000 nm.
D)1,000-10,000 nm.

Question 40

Poliovirus receptors are found

A)in cells of all tissues.
B)in spinal cord anterior horn cells only.
C)in nasopharynx,gut,and spinal cord anterior horn cells.
D)in gut cells only.

Question 41

Enveloped viruses may enter their host cells by engulfment within coated vesicles (endocytosis).

Question 42

Bacterial viruses are so named because they have prokaryotic cell structures similar to their bacterial hosts.
ASM

Question 43

Adult T-cell leukemia is thought to be caused by

A)herpesviruses.
B)retroviruses.
C)parvoviruses.
D)picornaviruses.

Question 44

0.2 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?

A)9.0 $\times$ 10⁵
B)4.5 $\times$ 10⁶
C)4.5 $\times$ 10⁷
D)9.0 $\times$ 10⁸

Question 45

Like bacteria and eukaryotic microorganisms,most viruses can be cultured using artificial media.

Question 46

In a plaque assay,the number of infectious virions is usually identical to the number of virus particles present.

Question 47

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

A)Its genome is a circular,single-stranded RNA molecule.
B)It needs a helper virus to infect host cells.
C)It produces one protein called the delta antigen.
D)All of the statements are true.

Question 48

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

A)cancer genes.
B)progenies.
C)oncogenes.
D)carcinogens.

Question 49

Viroids are of economic significance because they cause disease in

A)plants.
B)animals.
C)humans.
D)all of the choices

Question 50

Human cancer causing viruses most often have a ___________ genome.

A)ssDNA
B)dsDNA
C)ssRNA
D)dsRNA

Question 51

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

A)direct (electron microscopic)count
B)hemagglutination
C)plaque
D)PCR

Question 52

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

A)Human papilloma virus.
B)Hepatitis B virus.
C)Human T-cell lymphotropic virus.
D)Hepatitis A virus.

Question 53

Animal viruses have been cultivated in

A)suitable host animals.
B)embryonated eggs.
C)tissue cultures (monolayers of animal cells).
D)all of the choices

Question 54

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

A)They carry a cancer-causing gene into the cell.
B)They encode proteins that bind to and inactivate host cell proteins known as tumor suppressor proteins.
C)They produce defective interfering particles.
D)An expression of viral proteins results in abnormal expression of genes that regulate cell growth and reproduction.

Question 55

Hemagglutination is

A)the clumping together of red blood cells in the presence of a viral suspension.
B)the binding of iron in the process of a viral suspension.
C)the clumping together of infected cells in the presence of a viral suspension.
D)none of the choices

Question 56

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

A)Cultures of separated plant cells.
B)Whole plants.
C)Plant protoplast cultures.
D)All of these can be used to cultivate plant viruses.

Question 57

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

Question 58

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

Question 59

Which of the following is not true of viroids?

A)Viroids are small circular ssRNA molecules.
B)Viroids have no protein capsids.
C)Viroid RNA does not serve as mRNA nor does it direct the synthesis of mRNA.
D)Extracellular viroids have a lipid bilayer envelope.

Question 60

Some viruses cause abnormal growth of cells rather than destruction.This is called __________.

Question 61

Prions consist of proteins and have no apparent nucleic acid genome.

Question 62

Available evidence is consistent with the proposal that prion diseases are caused by infectious proteins.

Question 63

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

A)Scrapie.
B)Mad cow disease.
C)Kuru and Creutzfeldt-Jakob Disease.
D)All of the choices.

Question 64

Viroids are:

A)proteins that may infect man and other animals causing spongiform encephalopathy.
B)a class of so-called slow viruses.
C)a new class of small single stranded DNA viruses that infect some animals.
D)short infectious single stranded RNAs that can infect some plants.

Question 65

The mechanism of pathogenesis by prions may involve a conformational change in the prion protein (PrP)to an abnormal form.

Question 66

There are no known human diseases that have been linked to prions.

Question 67

Prions are of significance because they cause infections of

A)domestic animals and humans.
B)plants.
C)fungi.
D)prokaryotes.