Microbiology- Chapter 27

Acellular infectious agents

Viruses

Scientist that studies viruses

Virologist

Study of viruses

Virology

Complete virus particle.
Consists of >or = 1 DNA and RNA
may have additional layers
Cannot reproduce independent of living cells nor carry out cell division.
But can exist extracellularly

Virion

Simple organization

Viruses

Carry out cell division

Cellular organisms

Some obligate intracellular parasites

Cellular organisms

Unable to reproduce outside living cells

Viruses

Both DNA and RNA

Cellular organisms

Obligate intracellular parasities

Viruses

Complex organization

Cellular organisms

DNA or RNA but not both (one exception)

Viruses

True or False.
Virions infect all cell types

True

Bacterial viruses

Bacteriophages

Virions are classified into families based on:

Genome structure; Life cycle; Morphology; Genetic relatedness

localized area of cellular destruction and lysis

plaques

microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues

Cytopathic effects

Suitable animals
Embryonated eggs
Tissue (Cell) cultures

Hosts for animal viruses

Usually cultivated in broth or agar cultures of suitable, young, actively growing bacteria.
Broth cultures lose turbidity as viruses
Plaques observed on agar cultures

Hosts for Bacteriophages

Plant tissue cultures
Plant protoplast cultures
Suitable whole plants

Hosts for Viruses

Used to determine quantity of viruses in a samples

Virus assays

Two types of approaches for Virus assays

Count particles Measure concentration of infectious units

Types of count particles

Direct counts and Indirect counts

Made with an electron microscope

Direct counts

Determines highest dilution of virus that causes red blood cells to clumb together

Hemaggluntinaton assay

Dilutions of virus preparation maded and plated on lawn of host cells.
Number of plaques counted

Plaque assays

Plaque assays are expressed in what units?

Plaque forming units

Size range of virions

10-400 nm in diameter

How are most virions viewed

Through an electron microscope

True or False.
All virions contain a nucleocapside

True

Nucleic acid held with protein coat

Nucleocapsid

Protein coat that surrounds a viral genome
Protects genome and aids in transfers between host cells.

Capsid

Protein sub-units that make up capside

Protomer

Shaped like hollow tubes with protein walls

Helical capsids

Regular polyhedron with 20 equilateral triagular faces and 12 vertices

Icosahedral Capsid

Ring or knob shaped units made of five or six protomers

Capsomers

Five subunit capsomers

Pentamers (pentons)

Six subunit capsomers

Hexamers (hexons)

membrane structures surrounding some viruses

Viral envelope

proteins in envelop -virus specific

Peplomers (spikes)

Observed in some viruses
Associated with or are within capsid

Viral enzymes

True or False.
Viruses fit into the category of having helical or Icosahedral capsids

False

Largest animal virus

Poxvirus

Binal symmetry

Large bacteriophages

Having both icosahedral and helical symmetry

Binal symmetry

Sequence of nucleotides in genomic RNA= sequence of nucleotides in viral mRNA

Plus strand RNA viruses

Sequences of nucleotides in genomic RNA is complementary to viral mRNA.

Minus strand RNA viruses

Virions contains >1 unique RNA.

Segmented genomes

Sequences of viral infection

1. Attachment to host cell (Adsorption) 2. Entry 3. Uncoating of genome 4. Synthesis 5. Assembly 6. Release

specific receptor attachment that determine host preference (specific tissue, more than one host, more than one receptor, lipid rafts providing entry of virus)

Attachment (Adsorption)

Phage life cycle that culminates with host cell bursting, releasing virions

Lytic cycle

Phages that lyse their host during the reproductive cycle

Virulent phages

Specific surface structures on host to which viruses attach.
Specific for each virus
Can be protein, lipopolysaccharides, techioc acids, etc.

Receptor sites

Contains hydroxymethylcytosine instead of cytosine and is synthesized by two phages encode enzymes then HMC glucosylated

Synthesis of T4 DNA

Protects phage DNA from host restriction

HMC glucosylation

Enzymes that cleavage DNA at specific sequences

Endonucleases

Use of restriction endonucleases as a define mechanism against viral infection

Restriction

Aid in construction of procapsid

Scaffolding proteins

Attacks peptidoglycan

Endolysin

produces lesion in cell membrane

Holin

nonlytic relationship between a phage and its host

Lysogeny

integrated phage genome

Prophage

Infected bacterial host

lysogens

phages able to establish lysogeny

temperate phages

Rapid onset and relatively short duration

acute infections

can last many years

persistent infections

Virus almost always detectable.
Clinical symptoms mild or absent for long periods

Chronic virus infection

Virus stops reproducing and remains dormant for some time.

Latent infections

Deletion of mutant that cannot reproduce and slowsreproduction of normal virus

Detective interfering particle

Growth or lump of tissue

tumor

abnormal new cell growth or reproduction due to loss of regulation

neoplasia

reversion to a more primitive or less differentiated state

anaplasia

spread of cancerous cells through body

metastasis

Complex multistep process.
Involves oncogenes
Cancer causing genes
Many involved in regulation of cell growth and differentiation

Carcinogenesis

Infectious agents composed only of circular ssRNA

Viroids

infectious agent thought to be composed only of protein

Prions

Do not act as mRNA molecules
Cause disease to plants
Mechanism unknown
Some cause latent infections
RNA may be replicated by rolling circle method using host RNA polymerase

Viroids

Cause degenerative diseases in animales

Prions

When a viral genome is integrated into the host chromosome but does not result in the lysis of the host cell, it is referred to as
A. temperate infection.
B. avirulent infection
C. lysogemy
D. alytic infection

C. lysogemy

Which of the following is not true of viroids?
A. Viroids are small circular ssRNA molecules.
B. Viroids have no protein capsids.
C. Viroids do infect plants and some procaryotic cells
D. All of these are true of viroids.

D. All of these are true of viroids.

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.

D. Extracellular viroids have a lipid bilayer envelope.

Which of the following can serve as phage receptor sites?
A. lipopolysaccharides and teichoic acids
B. pili
C. membrane proteins
D. All of these can serve as phage receptor sites

D. All of these can serve as phage receptor sites

True or False
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.

False

Viral capsid protein subunits are called
A. auxomers
B. elastomers
C. protomers
D. viromers

C. protomers

Which of the following is true about viral envelopes?
A. The envelope proteins are virus specific
B. The envelope lipids and carbohydrates are derived from the host
C. Both of these answers are true
D. Neither of these answers are true

C. Both of these answers are true

Which of the following is most useful in determining the viability of a viral preparation?
A. a direct (electron microscopic) count
B. hemagglutination
C. a plaque assay
D. All are equally useful in determining the viability of a viral preparation

C. a plaque assay

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. both protect the viral genetic material and aid in the transfer of the viral genetic material between host cells
D. neither protect the viral genetic material nor aid in the transfer of the viral genetic material between host cells

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

Attachment of a bacteriophage to its host is mediated by
A. specific surface proteins on the bacteriophage
B. specific receptor proteins on the host cell
C. both specific surface proteins on the bacteriophage and specific receptor proteins on the host cell
D. either specific surface proteins on the bacteriophage or specific receptor proteins on the host cell but not both

C. both specific surface proteins on the bacteriophage and specific receptor proteins on the host cell

True or False
The injection mechanism used by bacteriophages whereby the nucleic acid penetrates the cell leaving the protein coat outside is not used by any known animal viruses.

False

A __________ genome exists as several separate, nonidentical molecules that may be packaged together or separately.
A. diploid
B. segmented
C. polyploid
D. fractionated

B. segmented

Viruses with single-stranded RNA as their genome for which the base sequence is the same as the viral mRNA are said to be __________ viruses.
A. plus-stranded
B. minus-stranded
C. mRNA-like
D. None of these

A. plus-stranded

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

D. release

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 are obligate intracellular parasites.
D. Viruses replicate by binary fission.

D. Viruses replicate by binary fission.

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 are obligate intracellular parasites.
D. All of these are true of viruses.

D. All of these are true of viruses.

45. The nucleic acids carried by viruses usually consist of
A. DNA
B. RNA
C. either DNA or RNA but not both simultaneously
D. both DNA and RNA simultaneously.

C. either DNA or RNA but not both simultaneously

47. Most important character in viral classification is:
A. nucleic acid type (DNA or RNA)
B. nucleic acid strandedness (single or double)
C. presence or absence of an envelope
D. all of the choices

A. nucleic acid type (DNA or RNA)

Viruses are subgrouped according to
A. nucleic acid type (DNA or RNA)
B. nucleic acid strandedness (single or double)
C. presence or absence of an envelope
D. all of the choices

D. all of the choices

Viruses with single-stranded RNA as their genome for which the base sequence is the same as the viral mRNA are said to be __________ viruses.
A. plus-stranded
B. minus-stranded
C. mRNA-like
D. none of these

A. plus-stranded

True or False
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.

False

Which of the following is (are) a function(s) of late viral proteins?
A. formation of the virion capsid
B. assembly of mature virions by noncapsid proteins
C. lysis of host cells
D. all of the choices

D. all of the choices

The protein coat surrounding the viral genome is called the
A. capsule
B. capsid
C. matrix
D. envelope

B. capsid

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. both protect the genetic material and in the transfer of genetic material between host cells
D. neither protect the viral genetic material nor aid in transfer of the viral genetic material between between host cells

C. both protect the genetic material and in the transfer of genetic material between host cells

True or False
Like bacteria and eucaryotic microorganisms, viruses can be cultured on artificial media.

False

Which of the following is true about viral envelopes?
A. The envelope proteins are virus specific.
B. The envelope lipids and carbohydrates are derived from the host
C. Both of these answers are true
D. Neither of these answers is true

C. Both of these answers are true

Animal viruses can be cultivated in
A. suitable host animals
B. embryonated eggs
C. tissue cultures (monolayers of animal cells)
D. all of these

D. all of these

Animal viruses can be cultivated in
A. suitable host animals
B. embryonated eggs
C. tissue cultures (monolayers of animal cells)
D. all of these
E. Only A and C

D. all of these

True or False
Bacterial viruses are so named because they have the same procaryotic cell structure as their bacterial hosts.

False

The nucleic acids carried by viruses usually consist of
A. DNA
B. RNA
C. either DNA or RNA but not both simultaneously
D. both DNA and RNA simultaneously

C. either DNA or RNA but not both simultaneously

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

D. release

A __________ assay is most useful for determining the viability of a viral preparation.
A. direct (electron microscopic) count
B. hemagglutination
C. plaque
D. PCR

C. plaque

The two major types of symmetry found in viruses are
A. icosahedral and radial
B. icosahedral and helical
C. helical and radial
D. radial and bilateral

B. icosahedral and helical

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

True

Which of the following morphologies are found among the bacteriophage?
A. tailless phage with icosahedral symmetry
B. tailed phage with binal symmetry
C. filamentous phage with helical symmetry
D. All of these are found in a bacteriophage

D. All of these are found in a bacteriophage

Some viruses do not have
A. capsid
B. nuclei acid
C. protomer
D. envelope

D. envelope

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

True

True or False
A few viruses are as large as smallest bacteria

True

The largest viruses known are the
A. herpesviruses
B. hepadnaviruses
C. adenoviruses
D. poxviruses

D. poxviruses

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 these

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

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

B. nucleocapsid

A complete virus particle is called a
A. capsid
B. nucleocapsid
C. virion
D. cell

C. virion

What is a feature of a virus with a segmented genome?
A. It has multiple chromosomes
B. It is haploid
C. It has a genome composed of separate pieces
D. It must have a DNA genome

C. It has a genome composed of separate pieces

Which of the following lists the steps of viral activity in the correct order, from start to finish?
A. Attachment, lysis, penetration, replication
B. Lysis, penetration, replication, attachment
C. Attachment, penetration, replication, lysis
D. Penetration, replication, attachment, lysis

A. Attachment, lysis, penetration, replication

True or False
Enveloped viruses may enter their host cells by engulfment within coated vesicles (endocytosis)

True

175. A biochemist wants to control the initial substrate-level phosphorylation that occurs in the yeast cells once glucose has crossed the plasma membrane. This means that he will:
A. have to prevent cAMP from entering the tracheal cells
B. have to prevent pyruvate reduction from occurring
C. have to prevent glycolysis from occuring in the mitochondria
D. have to prevent aerobic respiration in the cytoplasm
E. have to prevent glycolysis from occuring in the cytoplasm

E. have to prevent glycolysis from occuring in the cytoplasm

8. 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 can insert a promoter upstream of a cellular gene that regulates cell growth and reproduction.
C. They produce defective interfering particles.
D. An expression of viral proteins results in abnormal expression of genes that regulate cell growth and reproduction.

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10. T or F Parvoviruses are the simplest known animal viruses.

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11. Which of the following is (are) a function(s) of late viral proteins?
A. formation of the virion capsid
B. assembly of mature virions by noncapsid proteins
C. lysis of host cells
D. All of these are functions of late viral proteins

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15. Which of the following is most true of a viral DNA genome?
A. It uses the same four nitrogenous bases found in procaryotic and eucaryotic DNA.
B. It may have the normal bases found in procaryotic and eucaryotic DNA, or it may have one or more unusual bases.
C. It is usually composed of unusual bases unique to virues.
D. Viruses do not use DNA for their genome.

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21. Which of the following has been associated with a form of liver cancer?
A. human papilloma virus
B. hepatitus B virus
C. human T-cell lymphotropic virus
D. hepatitus A virus

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31. The most common type of molecule functioning as an animal virus receptor is a
A. lipoprotein
B. glycoprotein
C. phosphoprotein
D. teichoic acid

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46. Which of the following is most true of a viral DNA genome?
A. It uses the same four nitrogenous bases found in procaryotic and eucaryotic DNA.
B. It may have the normal bases found in procaryotic and eucaryotic 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.

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53. If all available enzyme molecules are binding substrate and converting it to product as rapidly as possible, the reaction is said to be proceeding at __________ velocity.
A. terminal
B. maximal
C. optimal
D. infinite

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60. General classes of enzymes found in cells include
A. lyase
B. medulase
C. allosterase
D. FAD

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86. When a rival genome is integrated into the host chromosome but does not result in the lysis of the host cell, it is referred to as
A. lysogeny
B. avirulent infection
C. temperate infection
D. alytic infection

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95. In a one-step growth experiment, the early period in which no infective virions are found even inside the infected host cells is called the _________ period.
A. latent
B. eclipse
C. rise
D. plateau

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100. A new antibiotic has been developed that will use noncompetitive inhibitor enzyme inhibition. This means that the
A. antibiotic will bind to the enzyme and alter the shape of the enzyme
B. antibiotic will bind to the substance and alter the shape of the substrate
C. antibiotic will bind to the enzyme-substrate complex and alter its shape
D. antibiotic will bind to the product that is being produced and alter its shape
E. antibiotic will bind to the receptor proteins embedded in the phospholipid bilayer, which will in turn close the channels

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101. One type of biochemical pathway regulation is referred to as feedback inhibition. This means that as the
A. cell produces more quantity of product through a biochemical pathway, the build up of that product will inhibit the activity of that product’s production
B. cell produces more quantity of product through a biochemical pathway, the activity will be increased or stimulated by the build up of that product
C. cell produces less quantity of product through a biochemical pathway, the activity will be inhibited by not having enough of that product
D. cell produces less quantity of product through a biochemical pathway, the activity of the substrate will be increased and it will exceed capacity of the pathway

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105. The decarboxylation of pyruvate produces
A. NADH
B. acetyl CoA
C. CO2
D. ATP
E. only A, B, and C are correct

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120. Who was the first person to propose that the cause of tobacco mosaic disease is an infectious agent different from bacteria because it could pass through a porcelain filter that retains all bacteria?
A. Jenner
B. Ivanowski
C. Beijerinck
D. Pasteur

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124. In order for bacteriophage to be released from the host by a lysis mechanism, enzymes are required that
A. halt ATP synthesis
B. stabilize the cytoplasmic membrane and cell wall
C. damage the cell wall and cytoplasmic membrane
D. degrade the host chromosome

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125. Entry of a virus into the lytic cycle after lysogeny has been established is called
A. lysogenic conversion
B. lysogenic reversion
C. induction
D. none of the choices

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126. T or F Glucosylation of hydroxymethylcytosine reidues protects phage T4 DNA from cleavage by bacterial restriction enzymes.

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129. Glycoprotein spikes protruding from the outer surface of viral envelopes may be involved in
A. viral recognition of host cells
B. viral attachment of host cells
C. both viral recognition of and viral attachment to host cells
D. neither viral recognition of nor viral attachment to host cells

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132. In a gradient density centrifugation, which of the following is true?
A. Particles will continue to settle toward the bottom of the tube for as long as the centrifugation is continued.
B. Particles will come to rest when the density of the surrounding medium is equal to the density of the particle even if the centrifugation is continued longer.
C. The smallest particle will sediment fastest.
D. Large particles will sediment farther than small particles.

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139. Methods useful for purification of viruses include
A. electron microscopy
B. differential gradient centrifugation
C. hemagglutination
D. X-ray diffraction

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143. Which of the following is (are) used by microorganisms to become resistant to a particular drug?
A. enzymatic inactivation of the drug
B. exclusion of the drug from the cell
C. an alternate metabolic pathway that bypasses the drug-sensitive step
D. all of these

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149. 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

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151. __________ are able to degrade infecting bacteriophage DNA, thus protecting the host cell.
A. Protection endonucleases
B. Protection exonucleases
C. Restriction endonucleases
D. Restriction exonucleases

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153. Enzymes found in virus particles
A. may be required for viral attachment to host cells.
B. may be involved in viral entry into host cells.
C. may be involved in the replication of viral nucleic acid.
D. All of these.

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156. T or F In viral infections, all of the viral genes are usually expressed prior to the replication of viral nucleic acid.

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170. Which of the following represents ways in which animal viruses damage their host cells?
A. disruption of lysosomes, releasing hydrolytic enzymes into the cell
B. alterations of the plasma membrane of cells that result in attacks by the host immune system
C. formation of inclusion bodies, causing direct physical disruption of cell structures
D. all of the choices

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171. The genetic code was deciphered in the 1960s in large part by the efforts of
A. Avery and Griffith
B. Khorana and Nirenberg
C. Watson and Crick
D. Hershey and Chase

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172. Which of the following is not a pyrimidine?
A. adenine
B. cytosine
C. thymine
D. uracil

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173. The genetic code is said to be __________ because more than one codon will specify a particular amino acid.
A. amibiguous
B. degenerate
C. multiplicative
D. repetitious

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