Microbiology: Chapter 27

Acellular infectious agents

Scientist that studies viruses

Study of viruses

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

Simple organization

Carry out cell division

Some obligate intracellular parasites

Unable to reproduce outside living cells

Both DNA and RNA

Obligate intracellular parasities

Complex organization

DNA or RNA but not both (one exception)

True or False. Virions infect all cell types

Bacterial viruses

Virions are classified into families based on:

localized area of cellular destruction and lysis

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

Suitable animals Embryonated eggs Tissue (Cell) cultures

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

Plant tissue cultures Plant protoplast cultures Suitable whole plants

Used to determine quantity of viruses in a samples

Two types of approaches for Virus assays

Types of count particles

Made with an electron microscope

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

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

Plaque assays are expressed in what units?

Size range of virions

How are most virions viewed

True or False. All virions contain a nucleocapside

Nucleic acid held with protein coat

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

Protein sub-units that make up capside

Shaped like hollow tubes with protein walls

Regular polyhedron with 20 equilateral triagular faces and 12 vertices

Ring or knob shaped units made of five or six protomers

Five subunit capsomers

Six subunit capsomers

membrane structures surrounding some viruses

proteins in envelop -virus specific

Observed in some viruses Associated with or are within capsid

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

Largest animal virus

Binal symmetry

Having both icosahedral and helical symmetry

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

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

Virions contains >1 unique RNA.

Sequences of viral infection

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

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

Phages that lyse their host during the reproductive cycle

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

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

Protects phage DNA from host restriction

Enzymes that cleavage DNA at specific sequences

Use of restriction endonucleases as a define mechanism against viral infection

Aid in construction of procapsid

Attacks peptidoglycan

produces lesion in cell membrane

nonlytic relationship between a phage and its host

integrated phage genome

Infected bacterial host

phages able to establish lysogeny

Rapid onset and relatively short duration

can last many years

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

Virus stops reproducing and remains dormant for some time.

Deletion of mutant that cannot reproduce and slowsreproduction of normal virus

Growth or lump of tissue

abnormal new cell growth or reproduction due to loss of regulation

reversion to a more primitive or less differentiated state

spread of cancerous cells through body

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

Infectious agents composed only of circular ssRNA

infectious agent thought to be composed only of protein

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

Cause degenerative diseases in animales

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

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.

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.

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

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.

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

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

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

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

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

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.

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

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

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

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.

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.

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.

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

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

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

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.

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

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

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

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

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

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

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

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

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

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

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

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

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

Some viruses do not have A. capsid B. nuclei acid C. protomer 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 or False A few viruses are as large as smallest bacteria

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

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

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

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

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

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

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