Lecture 4 Viruses and other Acellular infectious agents Flashcards
(168 cards)
1
Q
Acellular Agents
A
viruses, Viroids, Satellites, Prions
2
Q
Type of acellular agent that is protein and nucleic acid
A
Viruses
3
Q
Type of Acellular agent that is only RNA
A
Viroids
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Q
Type of Acellular agent that is only nucleic acids
A
Satellites
5
Q
Type of acellular agent that is only proteins
A
Prions
6
Q
Viruses are a major cause of _____
A
disease
7
Q
Viruses are important members of ____ world
A
aquatic
8
Q
Are viruses important in evolution
A
yes
9
Q
Viruses are important ____ systems in molecular biology
A
model
10
Q
Bacterial viruses are called ______
A
bacteriophages (phages)
11
Q
There are ___ archaeal viruses
A
few
12
Q
Most viruses are ____ viruses
A
eukaryotic (plants, animals, protists, and fungi)
13
Q
Viruses are classified into families based on
A
genome, structure, life cycle, morphology, genetic relatedness
14
Q
a complete virus particle is called a ____
A
virion
15
Q
General Properties of Viruses
A
- a complete virus particle
- consists of greater than or equal to 1 molecule of DNA or RNA enclosed in coat of protein
- May have additional layers
- cannot reproduce independent of living cells nor carry out cell division (but can exist extracellularly)
16
Q
A virion size range is about ______ nm in diameter and most viruses must be viewed with an _____-
A
10-400 nanometers, electron microscope
17
Q
All virions contain a _____ which is composed of ______ and a ______
A
nucleocapsid, which is composed of nucleic acid (DNA or RNA) and a protein coat (capsid)
18
Q
What are the protein subunits of a virion capsid called
A
capsomeres
19
Q
All Virion structure
A
- Nucleic Acid (DNA or RNA) (Single or double stranded)
- Capsid (Protein coat) (Protein subunits= Capsomeres)
20
Q
All virions contain a nucleocapsid which is composed of ____ and a _____ but some consist only of a nucleocapsid, others have additional components called ____
A
Nucleic acid (DNA or RNA) and protein coat (capsid), Envelopes
21
Q
The enveloped that surrounds the nucleocapsid of viruses usually has viral proteins called ____ inserted into it
A
spikes
22
Q
What are the three types of capsid symmetry
A
- helical
- icosahedral
- complex
23
Q
The envelope that surrounds some viruses is composed of
A
combination of lipids and carbohydrates , and proteins
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Q
Envelope lipids and carbohydrates are acquired from the ____. while envelope proteins are coded for by _____ and may even project form the envelope surface as ____
A
host, viral genes, spikes (also called peplomers)
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What is the function of envelope spikes (peplomers)
attachement to host cell surface
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General Characteristics of Viruses
- Obligatory intracellular parasites
- Contain DNA or RNA
- Contain a protein coat (note that the DNA/RNA and protein coat make up the nucleocapsid present in all viruses)
- Some are enclosed by an envelope
- Some viruses have spikes
- Most viruses infect only specific types of cells in one host
- Host range is determined by specific host attachment sites and cellular factors
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Large macromolecular structures which serve as protein coat of virus
Capsids
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Functions of virus capsid
Protect viral genetic material and aids in its transfer between host cells
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Virus Capsids are made of protein subunits called
protomers or capsomeres
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Viruses are classified by ___-
morphology
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examples of viruses classified by morphology
- helical viruses
- polyhedral viruses
- Enveloped Viruses
- Complex viruses
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Viruses shaped like hollow tubes with protein walls
Helical Capsids
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In helical capsids ____ self assemble
protomers
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In helical capsids the size of the capsid is a function of ______
nucleic acid
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Examples of helical viruses
- Rabies
| - Ebola hemorrhagic feber
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a _____ is a regular polyhedron with 20 equilateral faces and 12 vertices
icosahedron
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An icosahedron is a regular polyhedron with ____ equilateral faces and ___ vertices
20, 12
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______ are the most efficient way to enclose a space
Icosahedral capsids
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Icosahedral capsids are composed of ____, which are ring or knob-shaped units, each usually 5 or 6 protomers
Capsomers
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5 subunit capsomers are called
Pentamers (pentons)
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6 subunit capsomers are called
Hexamers (hexons)
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Pentamers are usually at the ____ of the icosahedron, whereas hexameters generally form its ____ and ____
vertices, edges and triangular faces
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Example of polyhedral virus
- Adenovirus
| - Poliovirus
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what is the largest animal virus
poxvirus
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Viruses that do not fit into the category of helical or icohedral capsids are called
Capsids of complex symmetry
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Examples of complex viruses
- Poxvirus
| - Large bacteriophages
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some Large bacteriophages have ____ symmetry
binal (head resembles icosahedral, tail is helical)
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many viruses are bound by an outer, flexible, membranous layer called the ____
envelope
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Animal virus envelopes (lipids and carbohydrates) usually arise from
host cell plasma or nuclear membranes
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Examples of enveloped viruses
- Influenza virus
- Herpes simplex virus
- rabies
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Envelope proteins, which are viral encoded, may project from the envelope surface as ____/____
spikes/peplomers
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functions of envelope protein, spikes/peplomers?
- involved in viral attachment to host cell
- used for identification of virus
- may have enzymatic or other activity
- may play role in nucleic acid replication
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The influenza virus has spikes that consist of enzyme ________, which functions in the release of mature virions from the host cell
Neuraminidase
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The influenza virus has spikes that consist of _____ proteins, so named because they bind virions to red blood cells and cause the cells to clump together- a process called ______
hemagglutinin, hemagglutination
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Do virions have a variety of enzymes
yes
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Some other virus enzymes are associated with the ____ or ____ but most are within the _____
envelope or capsid, but most are within the capsid
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Characteristics of the viral genome
- Diverse nature of genomes
- a virus may have single or double stranded DNA or RNA
- The length of the nucleic acid also varies form virus to virus
- Genomes can be segmented or circular
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What is the first step in the life cycle of a virus
attachment (often called absorption)
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Steps of animal viruses life cycle
- Attachement: viruses attach to cell membrane
- Penetration/Entry: Endocytosis or fusion
- Uncoating: viral or host enzymes
- Biosynthesis: Production of nucleic acid
- Maturation: Nucleic acid and capsid proteins assemble
- Release: by buddying (enveloped viruses) or rupture (lysis)
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HIV binds to what two proteins on human cells
CD4 and CCR5
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attachement (adsorption) of virus is ____ specific
receptor
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The receptor determines host preference for attachment (adsorption) of virus: may be ______, _______, _____, ____
may be specific tissue, may be more than one host, may be more than one receptor, maybe in lipid rafts providing entry of virus
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after attachment to the host cell, the virus's ____ or the entire ____ enter the cytoplasm
genome or entire nucleocapsid
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Viral entry and uncoating varies between ___ or ____ virus
naked or enveloped
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What are the 3 methods of viral entry and uncoating
- fusion of the viral envelope with host membrane; nucleocapsid enters
- endocytosis in vesicle; endosome (and endosomal enzymes) aid in viral uncoating
- Injection of nucleic acid
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RNA virus must carry in or synthesize the _____ proteins necessary to complete synthesis
proteins
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___ proteins are important in the assembly phase of the virus life cycle
late
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The ____,___, and ___ of the of a bacteriophage T4 are assembled separately.
baseplate, tail fibers, and head components
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for many viruses, so-called "virus factories" are generated. These are large ______ of either complete nucleocapsids or procapsids
paracrystalline clusters
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nonenveloped viruses ___ the host cell for release
lyse
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during the release of non enveloped viruses viral proteins may attack ____ or ____
peptidoglycan or membrane
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Lysozyme function in non enveloped viruses
attacks peptidoglycan in the host's cell wall
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What is the function of holin in non-enveloped viruses
creates holes in plasma membrane, thus enabling virus to move from the cytoplasm to the peptidoglycan
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Enveloped viruses are released via
budding
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Explain enveloped viruses being released via budding
- viral proteins are placed into host membrane
- nucleocapsid may bind to viral proteins
- envelope derived from host cell membrane, but may be Golgi, ER, or other
- Virus may use host actin tails to propel through host membrane
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Special features of Biosynthesis of single stranded DNA
Cellular enzyme transcribes viral DNA in nucleus
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Special features of Biosynthesis of double stranded DNA
- Cellular enzyme transcribes viral DNA in nucleus
| - Viral enzyme transcribes viral DNA in virion, in cytoplasm
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Special features of Biosynthesis ofDNA, reverse transcriptase
- Cellular enzyme transcribes viral DNA in nucleus; reverse transcriptase copies mRNA to make viral DNA
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Special features of Biosynthesis of RNA, + strand
Viral RNA functions as a template for synthesis of RNA synthesis of RNA polymerase which copies- strand RNA to make mRNA in cytoplasm
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Special features of Biosynthesis of RNA, - strand
Viral enzymes copies viral RNA to make mRNA in cytoplasm
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Special features of Biosynthesis of RNA, double-stranded
Viral enzyme copies - strand RNA to make mRNA in cytoplasm
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Special features of Biosynthesis of RNA, Reverse transcriptase
Viral enzyme copies viral RNA to make DNA in cytoplasm; DNA moves to nucleus
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Parvovirdae is what type of viral nucleic acid
DNA, single-stranded
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Herpesviridae, papovavidae, and poxviridae are what type of viral nucleic acid
DNA, Double-stranded
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Hepadnaviridae is what type of viral nucleic acid
DNA, reverse transcriptase
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Picornaviridae and Togaviridae are what type of viral nucleic acid
RNA, + strand
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Rhabdoviridae is what type of viral nucleic acid
RNA, - strand
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Reoviridae is what type of viral nucleic acid
RNA, double stranded
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Retroviridae is what type of viral nucleic acid
RNA, reverse transcriptase
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lack of information on ___ and ____ history makes viral classification difficult
origin and evolutionary
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A uniform classification system for virus taxonomy was developed in 1971 by the
Internal committee for Taxonomy of viruses (ICTV)
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Most current reports their are _____ viruses, ___ orders, ____ families, ___ subfamilies, and ____ genera
2,000, 6, 87, 19, 349
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Virus classification according to internal committee for taxonomy of viruses (ICTV) is based on numerous characteristics such as
- nucleic acid type
- presence or absence of envelope
- Capsid symmetry
- Dimensions of virion and capsid
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The alternative virus classification scheme was created by ____ and focuses on
David Baltimore, focuses on viral genome and process used to synthesize viral mRNA
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The baltimore classification system is based on ___ life cycles groups based on, which are
7
- double stranded (ds) DNA
- Single stranded (ss) DNA
- dsRNA
- ssRNA (+ or - strand)
- retrovirus
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Viral DNA can be integrated into a host cell chromosome as a provirus by _____
viral integrase
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What is a provirus
A stage in a retrovirus life cycle when viral DNA is integrated into a host cell chromosome by viral integrase
98
Bacteriophages can with be _____ or _____
virulent or temperate
99
Virulent phages only have one reproductive option which is
begin multiplying immediately upon entering its bacterial host, followed by release form the host by lysis
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T4 is an example of a _____ phage
virulent
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Temperate phages have two reproductive options which are
- they can multiply like a virulent phage and lyse the host cell
- or they can remain within the host without destroying it
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The relationship between a temperate phage and its host is called
lysogeny
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Lysogenic bacteria reproduce and in most other ways appear to be normal. however, they have two distinct characteristic, which are
- they cannot be reinffected by the same virus, that is they have immunity to superinfection
- as they reproduce, the prophage is replicated and inherited by progeny cells
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Many temperate phages integrate their genome into host genome (becoming _____ in a ______) in a relationship called lysogeny
Prophage, lysogenic bacterium
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what are the two advantages to lysogeny for virus
- phage remains viable but may not replicate
| - multiplicity of infection ensures survival of host cell
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under appropriate conditions infected bacteria will lyse and release temperate phage particles. This occurs when conditions in the cell cause the prophage to initiate synthesis of new phage particles , a process called ____
conditions in the cell cause the prophage to initiate synthesis of new phage particles , a process called induction
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Temperate phage changes ______ of its host. Phage may express ____ or ___
phenotype, pathogenic toxin or enzyme
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most archaeal viruses are ____
temperate
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Archaeal viruses can be ___ or __-
lytic or temperate
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______ infection results in cell death through lysis
cytocidal
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____ infections may last years
persistent
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Cytopathic effects (CPEs)
- degenerative changes
| - abnormalities
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a slow release of virus without cell death is caused by ___ infection
chronic viral infection
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activation of host proto-oncogene (human) or insertion of oncogene (other animals) can lead to
transformation into malignant cell
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Virus remains in asymptomatic host cell for long period is called ____ infection
latent infection
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Examples of latent infection
Cold sores, shingles
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in ____ viral infections disease process occurs over a long period; generally is fatal
Chronic viral infection
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examples of chronic viral infection
subacute sclerosing panencephalitis (measles virus)
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abnormal new cell growth and reproduction due to loss of regulation
neoplasia
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reversion of cell to a more primitive or less differentiated state
anaplasia
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___ tumors remain in place
benign
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Growth or lump of tissue
tumor
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Spread of cancerous cells throughout body
Metastasis
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carcinogenesis is a complex, ____ process, that often involves ____
multistep process, often involves oncogenes
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oncogenes may come from the virus or may be transformed
host proto-oncogenes (involved in normal regulation of cell growth/differentiation)
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Human herpesvirus 8 (HHV8) causes what kind of cancer
Several, including Kapok's sarcoma
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Epstein-Barr virus (EBV) causes what kind of cancer
Several, including Burkitt's lymphoma and nasopharyngeal carcinoma
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Hepatitis B virus causes what kind of cancer
Hepatocellular carcinoma
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Hepatitis C virus causes what kind of cancer
Liver cancer
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Human papillomaviruses (HPV) strains 6, 11, 16, and 18 cause what kind of cancer
Cervical cancer
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Human T-cell lymphotropic virus 1 (HTLV-1) causes what kind of cancer
T-Cell leukemia
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Possible mechanisms by which viruses cause cancer
- Viral proteins bind host cell tumor suppressor proteins
- Carry oncogene into cell and insert it into host genome
- Altered cell regulation
- Insertion of promotor or enhancer next to cellular oncogene
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The cultivation of viruses requires _____ of appropriate living host
inovulation
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Bacterial and Archaeal viruses are usually cultivated in ___ or ____ cultures of suitable, young, actively growing bacteria
- broth
| - agar
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Broth cultures lose ____ as viruses reproduce
turbidity
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____ are observed on agar cultures
Plaques
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Animal viruses are cultivated using ____ cultures
Tissue (Cell)
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Localized area of cellular destruction and lysis that enlarges as the virus replicates (on tissue (cell) culture)
Viral plaques
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Microscopic or macroscopic degenerative changes or abnormalities in host cells and tissues
Cytopathic effects (CPEs)
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Hosts for plant viruses
- Plant tissue cultures
- Plant protoplast cultures
- Suitable whole plants
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Plant viruses in suitable whole plants may cause ____ lesions or ______
localized necrotic lesions or generalized symptoms of infection
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How to quantify virus on culture
- direct counting- count viral particles
| - Indirect counting by an observation of virus- hemagglutination assay and plaque assays
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PFU/ml=
number of plaques/sample dilution
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explain plaque assays
- indirect assay that determines virion numbers based on their infectivity.
- dilutions of virus preparation are made and planted on lawn of host cells. Then the plaques are counted. results expressed as plaque-forming units (PFU)
- PFU/ml = number of plaques/sample dilution
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what does a high multiplicity of infection mean (MOI)
more phages in an environment than there are host cells
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In plaque assays when the multiplicity of infection (MOI) is very low, each plaque in a layer of host cells is assumed
to have arisen from the multiplication of a single virion
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The ____ dose is the dilution that contains a concentration (dose) of virions large enough to destroy 50% of the host cells or organisms
lethal dose (LD50)
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The _____ dose is the dose that causes 50% of the host organisms to become infected
infectious dose (ID50)
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____ are covalently closed, circular ssRNAs, about 250 to 370 nucleotides long
Viroids
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Viroids replicate by a host cell enzyme called ________
DNA-dependent RNA polymerase
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Viroids cause ____ disease
plant
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Do viroids encode gene products
No!!!
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some data suggest that viroids cause disease by triggering a eukaryotic response called _____, which normally functions to protect against infection by darn viruses
RNA silencing
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Infectious nucleic acids (DNA or RNA)
infectious nucleic acids
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Satellite viruses encode their own _____ proteins when helped by a ____ virus
capsid, helper
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Satellite RNAs/DNAs do not encode their own ______
capsid proteins
157
satellites differ from viroids in that they
- may encode one or more gene products
| - need a helper virus to replicate and infect host cells
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satellites are divided into what three types
Satellite viruses, Satellite RNAs, and satellite DNAs
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Satellite viruses encode their own ______, whereas satellite RNAs and DNAs do not
capsid proteins
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Human Hepatitis D virus is a _____ and requires ______ as a helper virus for replication
human hepatitis D virus is a satellite and requires Human hepatitis B virus as a helper virus for replication
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Proteinaceous infectious particle
Prions
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Examples of prions
- Scrapie in sheep
- Bovine spongiform encephalopathy (BSE) or mad cow disease
- Creutzfeldt-Jakob disease (CJD) and variant CJD (vCJD) in humans
- Kuru in humans
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priions cause a variety of
degenerative diseases in humans and animals
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PrP^c stands for
prion protein in normal form
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PrP^Sc stands for
(scrapie-associated) prion protein in the abnormal form
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All prion caused diseases have ____ effective treatment, and result in
No effective treatment, and result in progressive degeneration of the brain and eventual death
167
Interaction of PrP^Sc with PrP^c may cause PrP^c to ____ and ____
crosslink and trigger apoptosis
168
What distinguishes a chronic viral infection from a latent viral infection?
The infectious virus gradually builds up over a long period of time
