Microbiology: Chapter 27 – Flashcards

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Acellular infectious agents
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Viruses
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Scientist that studies viruses
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Virologist
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Study of viruses
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Virology
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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
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Virion
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Simple organization
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Viruses
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Carry out cell division
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Cellular organisms
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Some obligate intracellular parasites
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Cellular organisms
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Unable to reproduce outside living cells
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Viruses
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Both DNA and RNA
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Cellular organisms
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Obligate intracellular parasities
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Viruses
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Complex organization
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Cellular organisms
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DNA or RNA but not both (one exception)
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Viruses
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True or False. Virions infect all cell types
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True
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Bacterial viruses
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Bacteriophages
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Virions are classified into families based on:
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Genome structure; Life cycle; Morphology; Genetic relatedness
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localized area of cellular destruction and lysis
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plaques
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microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues
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Cytopathic effects
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Suitable animals Embryonated eggs Tissue (Cell) cultures
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Hosts for animal viruses
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Usually cultivated in broth or agar cultures of suitable, young, actively growing bacteria. Broth cultures lose turbidity as viruses Plaques observed on agar cultures
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Hosts for Bacteriophages
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Plant tissue cultures Plant protoplast cultures Suitable whole plants
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Hosts for Viruses
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Used to determine quantity of viruses in a samples
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Virus assays
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Two types of approaches for Virus assays
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Count particles Measure concentration of infectious units
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Types of count particles
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Direct counts and Indirect counts
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Made with an electron microscope
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Direct counts
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Determines highest dilution of virus that causes red blood cells to clumb together
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Hemaggluntinaton assay
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Dilutions of virus preparation maded and plated on lawn of host cells. Number of plaques counted
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Plaque assays
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Plaque assays are expressed in what units?
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Plaque forming units
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Size range of virions
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10-400 nm in diameter
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How are most virions viewed
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Through an electron microscope
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True or False. All virions contain a nucleocapside
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True
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Nucleic acid held with protein coat
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Nucleocapsid
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Protein coat that surrounds a viral genome Protects genome and aids in transfers between host cells.
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Capsid
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Protein sub-units that make up capside
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Protomer
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Shaped like hollow tubes with protein walls
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Helical capsids
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Regular polyhedron with 20 equilateral triagular faces and 12 vertices
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Icosahedral Capsid
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Ring or knob shaped units made of five or six protomers
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Capsomers
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Five subunit capsomers
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Pentamers (pentons)
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Six subunit capsomers
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Hexamers (hexons)
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membrane structures surrounding some viruses
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Viral envelope
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proteins in envelop -virus specific
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Peplomers (spikes)
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Observed in some viruses Associated with or are within capsid
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Viral enzymes
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True or False. Viruses fit into the category of having helical or Icosahedral capsids
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False
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Largest animal virus
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Poxvirus
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Binal symmetry
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Large bacteriophages
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Having both icosahedral and helical symmetry
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Binal symmetry
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Sequence of nucleotides in genomic RNA= sequence of nucleotides in viral mRNA
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Plus strand RNA viruses
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Sequences of nucleotides in genomic RNA is complementary to viral mRNA.
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Minus strand RNA viruses
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Virions contains >1 unique RNA.
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Segmented genomes
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Sequences of viral infection
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1. Attachment to host cell (Adsorption) 2. Entry 3. Uncoating of genome 4. Synthesis 5. Assembly 6. Release
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specific receptor attachment that determine host preference (specific tissue, more than one host, more than one receptor, lipid rafts providing entry of virus)
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Attachment (Adsorption)
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Phage life cycle that culminates with host cell bursting, releasing virions
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Lytic cycle
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Phages that lyse their host during the reproductive cycle
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Virulent phages
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Specific surface structures on host to which viruses attach. Specific for each virus Can be protein, lipopolysaccharides, techioc acids, etc.
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Receptor sites
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Contains hydroxymethylcytosine instead of cytosine and is synthesized by two phages encode enzymes then HMC glucosylated
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Synthesis of T4 DNA
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Protects phage DNA from host restriction
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HMC glucosylation
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Enzymes that cleavage DNA at specific sequences
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Endonucleases
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Use of restriction endonucleases as a define mechanism against viral infection
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Restriction
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Aid in construction of procapsid
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Scaffolding proteins
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Attacks peptidoglycan
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Endolysin
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produces lesion in cell membrane
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Holin
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nonlytic relationship between a phage and its host
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Lysogeny
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integrated phage genome
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Prophage
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Infected bacterial host
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lysogens
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phages able to establish lysogeny
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temperate phages
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Rapid onset and relatively short duration
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acute infections
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can last many years
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persistent infections
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Virus almost always detectable. Clinical symptoms mild or absent for long periods
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Chronic virus infection
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Virus stops reproducing and remains dormant for some time.
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Latent infections
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Deletion of mutant that cannot reproduce and slowsreproduction of normal virus
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Detective interfering particle
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Growth or lump of tissue
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tumor
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abnormal new cell growth or reproduction due to loss of regulation
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neoplasia
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reversion to a more primitive or less differentiated state
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anaplasia
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spread of cancerous cells through body
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metastasis
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Complex multistep process. Involves oncogenes Cancer causing genes Many involved in regulation of cell growth and differentiation
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Carcinogenesis
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Infectious agents composed only of circular ssRNA
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Viroids
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infectious agent thought to be composed only of protein
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Prions
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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
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Viroids
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Cause degenerative diseases in animales
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Prions
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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
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C. lysogemy
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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.
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D. All of these are true of viroids.
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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.
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D. Extracellular viroids have a lipid bilayer envelope.
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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
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D. All of these can serve as phage receptor sites
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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.
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False
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Viral capsid protein subunits are called A. auxomers B. elastomers C. protomers D. viromers
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C. protomers
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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
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C. Both of these answers are true
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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
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C. a plaque assay
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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
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C. both protect the viral genetic material and aid in the transfer of the viral genetic material between host cells
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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
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C. both specific surface proteins on the bacteriophage and specific receptor proteins on the host cell
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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.
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False
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A __________ genome exists as several separate, nonidentical molecules that may be packaged together or separately. A. diploid B. segmented C. polyploid D. fractionated
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B. segmented
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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
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A. plus-stranded
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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
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D. release
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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.
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D. Viruses replicate by binary fission.
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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.
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D. All of these are true of viruses.
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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.
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C. either DNA or RNA but not both simultaneously
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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
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A. nucleic acid type (DNA or RNA)
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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
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D. all of the choices
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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
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A. plus-stranded
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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.
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False
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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
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D. all of the choices
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The protein coat surrounding the viral genome is called the A. capsule B. capsid C. matrix D. envelope
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B. capsid
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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
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C. both protect the genetic material and in the transfer of genetic material between host cells
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True or False Like bacteria and eucaryotic microorganisms, viruses can be cultured on artificial media.
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False
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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
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C. Both of these answers are true
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Animal viruses can be cultivated in A. suitable host animals B. embryonated eggs C. tissue cultures (monolayers of animal cells) D. all of these
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D. all of these
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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
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D. all of these
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True or False Bacterial viruses are so named because they have the same procaryotic cell structure as their bacterial hosts.
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False
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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
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C. either DNA or RNA but not both simultaneously
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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
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D. release
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A __________ assay is most useful for determining the viability of a viral preparation. A. direct (electron microscopic) count B. hemagglutination C. plaque D. PCR
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C. plaque
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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
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B. icosahedral and helical
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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
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True
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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
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D. All of these are found in a bacteriophage
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Some viruses do not have A. capsid B. nuclei acid C. protomer D. envelope
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D. envelope
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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.
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True
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True or False A few viruses are as large as smallest bacteria
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True
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The largest viruses known are the A. herpesviruses B. hepadnaviruses C. adenoviruses D. poxviruses
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D. poxviruses
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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
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A. the clumping together of red blood cells in the presence of a viral suspension
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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
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B. nucleocapsid
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A complete virus particle is called a A. capsid B. nucleocapsid C. virion D. cell
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C. virion
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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
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C. It has a genome composed of separate pieces
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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
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A. Attachment, lysis, penetration, replication
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True or False Enveloped viruses may enter their host cells by engulfment within coated vesicles (endocytosis)
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True
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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
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E. have to prevent glycolysis from occuring in the cytoplasm
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