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test 3
Viruses, Viroids & Prions
155
Microbiology
Undergraduate 2
11/08/2009

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Term
Acellular (noncellular)
Definition
infectious agent consisting of nucleic acid (genome) enclosed in a protein coat called a capsid (virally encoded)
Term
naked virus
Definition
If there is no additional covering other than capsid
Term
enveloped viruses
Definition
Many viruses that infect animals and humans have lipid bilayer membrane or envelope
Term
Viral envelope is of host ceInfection typically leads toll origin
Definition
acquired from cytoplasmic membrane or nuclear membrane during viral release.
Term
Viral nucleic acid (genome)
Definition
can be either DNA or RNA (dsDNA, ssDNA, dsRNA, ssRNA) - but not both!
Term
monopartite genome
Definition
The entire genome may consist of either one nucleic acid molecule
Term
segmented or multipartite genome
Definition
several nucleic acid segments
Term
virion
Definition
is the extracellular/transmissible infectious form of a virus
Term
Main function of virion/virus
Definition
deliver its DNA or RNA genome into host cell so that the viral genome can be replicated (make more nucleic acid) and then the genes encoded on that nucleic acid are expressed (transcribed into mRNA and translated into protein) by the host cell to make more virus.
Term
Infection typically leads to
Definition
rapid virus replication, but not always - latent phage, DNA tumor viruses transform only, slow viral infections
Term
Nonliving
Definition
No cell membrane, no metabolic activity or energy generating capabilities, no ribosomes, rely on host metabolic and biosynthetic machinery to produce more viral particles
Term
cannot reproduce on their own - only reproduce inside living host cells, obligate intracellular parasites
Definition
Non-living viruses
Term
Some viruses replicate in
Definition
cytoplasm and some in nucleus - viral replication site in host cell is dependent upon type of viral nucleic acid
Term
Viral size range
Definition
10 nm - 400 nm
Term
Viruses differ in the following characteristics
Definition
  • Type of genetic material/nucleic acid they contain
  • Mode of replication
  • Kinds of cells they infect
  • Routes of infection (respiratory, GI, urogenital, skin, eyes, etc)
  • Shape/morphology
  • Presence of an envelope
  • Size
Term
Primary criteria for taxonomic classification of animal viruses based on:
Definition
Morphology (size, shape, etc); type of nucleic acid (DNA, RNA - ss, ds, linear, circular, segmented, etc.); and presence of envelope.
Term
host ranges
Definition
Most can only infect specific types of cells of one host species - however, some can “jump species” and infect new hosts (ex. influenza) - these viruses are often responsible for epidemics/pandemics!
Term
host ranges are often determined by
Definition
requirements for specific attachment
RECEPTORS
availability of cellular factors for viral multiplication
Term
proteins/glycoproteins
Definition
The attachment of a virus to a host cell is a highly specific process involving the interaction of proteins/glycoproteins on surface of virus with receptors (proteins/glycoproteins) on surface of a susceptible host cell. Only after attachment has occurred can virus or its genome penetrate host cell.
Term
Viral Nucleic Acid Structure
Definition
Either DNA or RNA, never both!
Single-stranded or double-stranded
ssDNA, dsDNA, ssRNA, dsRNA
Linear or circular
Some in several segments
a few thousand nucleotides – 250,000
Term
Capsid
Definition
protein coat surrounding nucleic acid
subunits are called capsomeres
some single protein, some mosaic
there are a variety of shapes
Term
Envelope
Definition
only found in SOME viruses
lipid bilayer with proteins & carbohydrates surrounding the capsid
(lipid bilayer membrane and some proteins in it from host cell – viral glycoproteins inserted)
Term
Spikes
Definition
(virally-encoded glycoproteins) - some viruses
project from the envelope or capsid
serve to attach virions to specific receptors on the surface of host cells
change composition to evade immune system
Term
Viruses are classified on basis of their capsid structure
Helical - resemble long rods
ex. Ebola, Rabies, Tobacco Mosaic Virus
Polyhedral - many sided, roughly spherical
Icosahedron – 20 triangle faces, 12 corners
ex. Adenovirus, Poliovirus
Enveloped – helical or polyhedral
ex. Influenzavirus, Herpes Simplex Virus
Complex – complicated structures
ex. bacteriophage
Definition
Helical
Polyhedral
Icosahedron
Enveloped
Complex
Term
Helical
Definition
resemble long rods
ex. Ebola, Rabies, Tobacco Mosaic Virus
Term
Polyhedral
Definition
many sided, roughly spherical
Icosahedron – 20 triangle faces, 12 corners
ex. Adenovirus, Poliovirus
Term
Enveloped
Definition
helical or polyhedral
ex. Influenzavirus, Herpes Simplex Virus
Term
Complex
Definition
complicated structures
ex. bacteriophage
Term
[image]
Definition
Term
Bacteriophages (phages) - Complex
Definition
These viruses infect only bacteria

Phage may attach to bacterial cell walls, fimbriae, or pili.

Only viral nucleic acid enters bacteria, capsid remains outside

Have been used as an alternative to antibiotics in foreign countries - “phage therapy”
Term
Excellent models for understanding basics of viral biology
Definition
Bacteriophages:
- Inexpensive

- Easy to grow and study in lab
Term
Overview of Virus Life Cycle
Definition
After attachment and entry into host cell, virus hijacks biosynthetic and protein synthesizing abilities of cell in order to replicate viral nucleic acid, make viral proteins and arrange its escape from cell.
Term
Differences between prokaryotic and eukaryotic cells
Definition
affect how and where viruses replicate!
Term
PROKARYOTES
Definition
- DNA replication, transcription, and translation occur in cytoplasm.
Term
EUKARYOTES
Definition
DNA replication and transcription occur in nucleus, while translation occurs in cytoplasm
Term
prokaryotes life cycle
Definition
only viral nucleic acid enters cell, in animal viruses, entire virus enters cell by endocytosis, and virus must uncoat (capsid removed)
Term
The virus life cycle can be divided into five main stages:
Definition
1. Attachment (adsorption)
2. Penetration
3. Viral synthesis
4. Assembly and packaging of new virus particles
5. Virus release
Term
1. Attachment (adsorption)
Definition
of virus to host cell
Term
2. Penetration
Definition
virus or viral nucleic acid enters host cell (this process differs between bacteriophage and animal viruses). For animal viruses - viral uncoating.
Term
3. Viral synthesis
Definition
production of viral protein and nucleic acid.
How this occurs depends on whether the infecting viral nucleic acid is DNA or RNA
Term
4. Assembly and packaging of new virus particles
Definition
assembly of viral genomes, proteins, enzymes into complete progeny virions
Term
5. Virus release
Definition
from infected host cell (may or may not result in death of host cell - this process differs between bacteriophage and animal viruses - cell lysis or enveloped viruses bud off)
Term
Bacteriophage (virus that infect bacteria)
Definition
injects its DNA into the bacterial cell
release lysozyme to break down bacterial cell wall
capsid remains outside
Term
Naked animal viruses are taken into the cell by direct penetration or by injection (less common)
Definition
direct penetration or by injection (less common)
Term
Enveloped animal viruses can enter via
Definition
1) fusion (like HIV and Herpes) = virus envelope fuses with the host cell membrane & releases capsid into the cell; OR 2) endocytosis (Influenza virus)
Term
once inside the cell, animal viruses ...
Definition
uncoat
proteolytic enzymes from the cell break down the viral capsid
Term
DNA viruses biosynthesis
Definition
DNA transcribed into mRNA which is then translated into viral proteins
DNA is also replicated to make more viral genomes
takes place in the host nucleus (except Poxviruses)
Term
RNA viruses (biosynthesis)
Definition
some can be used directly as mRNA (+ strand)
some cannot be used directly as mRNA (- strand)
in some, RNA needs to be copied first into DNA by a reverse transcriptase
usually takes place in the host cytoplasm (exception Influenza Virus)
Term
Bacteriophage - Lytic Phages
Definition
Lytic phages infect cell
Make more phages within the cell
Phages burst out of the infected cell
Infected cell is lysed
ie. T-even Phage
Term
Lysogenic (temperate) phages
Definition
infect the cells but do not kill the cells
Term
a prophage
Definition
Viral DNA is incorporated into the host’s chromosome
Term
Bacteriophage - Lysogenic Phages
Definition
Spontaneous event, chemicals & UV are capable of pushing prophages to becoming lytic
Term
Importance of Lysogeny
Definition
Cells are immune to reinfection/superinfection with the same phage
Term
Phage Conversion
Definition
host cell may exhibit new properties
Prophage carries genes
Many pathogens get toxins this way
Term
Transduction (specialized and generalized)
Definition
Phage “mistakenly” packages bacterial DNA sequences instead of viral DNA in its capsid.

Specialized transduction - phage can only package certain/select bacterial genes
Generalized transduction - phage can package any region of bacterial DNA
Term
Lifestyle of ANY virus designed to
Definition
maximize production of progeny virus particles!
Term
Upon entering host cell, virus must ensure that two things happen
Definition
#1) Some nucleic acid must be used to make more genomic nucleic acid for packaging into new progeny virions (viral replication)

#2) Some nucleic acid must be transcribed and translated into viral proteins (viral replication)
Term
Animal virus reproduction stages
Definition
Attachment/adsorption
Penetration
Uncoating
Viral synthesis - how this occurs depends on whether the infecting viral nucleic acid is DNA or RNA
Assembly of capsids and packaging of new virus particles
Virus release
Term
Most DNA viruses enter the nucleus where they
Definition
“hijack” the host cell’s DNA replication machinery to make more virus. (Exception, smallpox, DNA virus that encodes its own DNA replication machinery and thus remains in cytoplasm).
Term
most RNA viruses replicate in the cytoplasm
Definition
because the enzymes used to replicate viral RNA are virally encoded.
Term
In general, for DNA viruses:
Definition
Most DNA viruses (with exception of smallpox) replicate in the nucleus and use host enzymes to replicate viral DNA.
Term
Viral genome is replicated using
Definition
host cell DNA polymerase (nucleus) and transcribed by host cell RNA polymerase (nucleus).
Term
In general, for RNA viruses
Definition
Most RNA viruses replicate in the cytoplasm because enzymes used to replicate viral RNA are virally encoded.
*RNA viruses have higher rates of mutation!
Term
(+) strand RNA viruses
Definition
the mRNA can be directly translated by host cell to make viral proteins. However, host cell cannot replicate RNA, thus, virus encodes an enzyme to replicate the ssRNA genome and host translates viral proteins for capsid.

- Retroviruses carry enzyme reverse transcriptase, which copies RNA into DNA – they replicate through a DNA intermediate
Term
(-) strand RNA viruses
Definition
(-) RNA strand must function as template to make a complementary strand of + RNA before any translation can occur. Host translation machinery can only make proteins from (+) strand RNA.
Term
Viral genomes contain information which:
Definition
・ ensures replication of viral genomes
・ ensures packaging of genomes into virions
・ alters structure and/or function of the host cell to a greater or lesser degree
Term
VIRAL STRATEGY
Definition
Viral strategy refers to the manner in which each virus carries out the above functions. Since a virus is an intracellular parasite, it has to operate within limits imposed by the host cell, or circumvent these limitations.
Term
Antigenic shift
Definition
Genome Reassortment, abrupt major change in antigenicity of virus; results from recombination of genes between different viruses.
Term
Antigenic drift
Definition
minor change of antigen on surface of virus that continually happens over time - due to accumulation of mutations in viral genome
Term
Growing Viruses in the Lab
Definition
Bacterial viruses (bacteriophage) have proved useful model systems because the host cells (bacteria) are easily to grow and manipulate in culture.
Term
Growing Bacteriophages In Lab
Definition
In suspensions or in cultures on solid media
Plaque Method – solid media
Bacteriophages, host bacteria & liquid agar is poured into a petri dish
Following a few cycles of infection, the bacteria surrounding the original virus are all destroyed
Clear area - plaque
Each plaque corresponds to one virus
Concentrations given in pfu
(plaque-forming units)
Term
Growing Animal Viruses in the Lab
Definition
Cell lines are observed for cytopathic (damaging) effects elicited by viruses and viral neutralization studies prior to human clinical trials
Term
Viruses and Cancer
Definition
Cancers are the result of a disruption of the normal restraints on cellular proliferation

Viruses cause cancer by altering the normal host cellular proliferation cycles resulting in a loss of growth control
Term
Proto-oncogenes
Definition
normal genes that if altered, can make a normal cell cancerous (involved in cellular proliferation)
Term
Oncogenes
Definition
a proto-oncogene that has been altered and can produce a protein that makes a cell cancerous
Term
Oncogenic Viruses
Definition
capable of inducing tumors
Term
PRIONS
Definition
Very stable - Conventional disinfection does not inactivate prions
Term
Pathogenesis of prions
Definition
Fragments accumulate forming plaques (insoluble aggregates of protein), but it still is not known how this kills cells
Term
The abnormal form of the protein
Definition
acquires a different shape/conformation than normal form (PrPc), this change in shape alters function of protein!
Term
VIROIDS
Definition
A single piece of RNA
Smaller than viral RNA
300-400 nucleotides
No protein coat
Does not code for a protein
Causes plant diseases
Term
pathogen
Definition
microorganism capable of causing disease
Term
epidemiology
Definition
the study of the cause and transmission of disease within a population
An epidemiologist studies where and when a disease occurs and how it is spread in populations
Term
infection
Definition
invasion or colonization of the body by pathogenic microorganisms
Term
Disease
Definition
an abnormal state in which part or all of the body is not properly adjusted or incapable of performing its normal functions
Infection may occur without detectable disease
Term
normal flora
Definition
permanent residents; usually don’t cause disease (exception - if introduced into unusual site in body
Term
transient microbiota
Definition
those present only temporarily, vast majority do not cause disease - but some do under right conditions (i.e. when host is not healthy).
Skin, eyes, upper respiratory, mouth, intestines, urogenital system
Term
Normal Microbiota
Definition
Although continue to add transient microbiota, most of resident microbiota initially established in early months of life.
Term
Three main types of symbiosis:
Definition
mutulaism
commensalism
parasitism
Term
Mutualism
Definition
both members benefit from interaction
(ex., bacteria in your colon produce vitamins and in turn receive nutrient rich environment to live)
Term
Commensalism
Definition
one benefits, the other is unaffected
(ex., Staphylococcus aureus growing on skin)
Term
Parasitism
Definition
one benefits, the other is harmed
(ex., infection of host by microbial pathogen)
Term
Types of Microbial Pathogens:
Definition
- Opportunistic
- Obligate
Term
Opportunistic Pathogen
Definition
microbes which do not cause disease in the healthy host
But can cause disease when host has weakened immune defense or when change in normal microbiota due to antibiotic treatment
opportunistic infections
Term
Exposure/Portals of entry for pathogens
Definition
Skin
Ears
Eyes
Nose
Mouth
Mammary glands
Urethra
Vagina
Anus
Term
Koch’s Postulates - How to prove that a particular pathogen causes a disease:
Definition
The pathogen must be present in every case of the disease -i.e., the pathogen should be found in diseased tissue but not healthy tissue.
The pathogen must be isolated from the diseased host and grown in pure culture.
The pathogen from the pure culture must cause the disease when it is inoculated into a healthy human or laboratory animal.
The pathogen must be isolated from the inoculated human/animal & must be shown to be the original organism.
Term
Exception to Postulate 1
Definition
some pathogens are found in both healthy hosts and those with disease.
Term
Exception to Postulate 2
Definition
not all pathogens can be grown in pure culture - unique culture requirements
Term
Exception(s) to Postulate 3
Definition
a) suitable animal models are not available for all pathogens; b) how well does animal model mimic the disease in humans?
Term
Other Exceptions to Koch’s Postulates
Definition
Microbiota shift diseases - diseases caused by shifts in microbial populations (ex. periodontal disease) - problems for third postulate since difficult to produce specific populations shifts in lab animals
Term
Symptoms
Definition
subjective changes in body function that can be felt by patient
Term
Signs
Definition
objective changes that can be observed and measured
Ex. nausea, pain, headache, dizziness, and fatigue = symptoms
Ex. vomiting, swelling, rash, redness, fever = signs
Term
Syndrome
Definition
a particular group of signs or symptoms that usually accompanies a specific disease - ex., AIDS characterized by weight loss, malaise, loss of certain white blood cells, diarrhea, pneumonia, toxoplasmosis, and tuberculosis
Term
Infectious
Definition
caused by infectious agents
Term
Non-infectious
Definition
caused by any other factor besides infectious agents
Term
Communicable
Definition
spread from one host to another
Term
Contagious
Definition
EASILY spread from one person to another
Term
Non-communicable
Definition
from normal flora or from the environment and cause disease when introduced into the body (not transmitted from one person to another)
Term
Congenital
Definition
diseases present at birth
Term
Nosocomial
Definition
infections obtained from hospital treatment (or other health care setting like nursing home, dental office, etc).
Term
Idiopathic
Definition
cause unknown
Term
Zoonoses
Definition
occur primarily in wild and domestic animals but can be transmitted to humans
Term
Incidence
Definition
the fraction of the population contracting a disease per time period - i.e. # of new cases of disease in a given time period
Term
Prevalence
Definition
the fraction of the population having a disease at a specified time - i.e. total number of cases, both new and already existing, in a given population at a given time.
Term
Sporadic disease
Definition
occurs occasionally
Term
Endemic disease
Definition
constantly present
Term
Epidemic disease
Definition
large number of people acquiring a disease in a given geographical area in a short period of time - (or whenever a disease occurs at a greater frequency than is usual for an area or population).
Term
Pandemic
Definition
worldwide outbreak
Term
ID50
Definition
number of microorganisms required to cause infection in 50% of experimentally infected animals or humans
Term
LD50
Definition
number of microorganisms (or the amount of toxin) required to kill half of the animals experimentally inoculated
Virulence of organism
Potency of toxin
Term
Indirect relationship between LD50 and virulence
Definition
A lower LD50 means the organism is more virulent! i.e. it takes fewer organisms to cause disease. “Less is worse”!
Term
Pathogens have a variety of traits called virulence factors that enable them to cause disease:
Definition
Adhere to host cells
Enter host cells
Gain access to nutrients
Escape detection by immune system
Some of these are secreted virulence factors
Term
multiple traits often important for the organism to cause disease
Definition
Virulence is multifactorial
Term
Once inside, most bacteria attach to host tissue
Definition
Adherence is necessary step for their pathogenicity - fluids may wash bacteria away if they do not adhere to host cells.
Term
Bacteria use surface molecules adhesins or ligands
Definition
Bacterial surface proteins that bind to host cell surface receptors (usually glycoproteins or lipoproteins)
located on pili, fimbriae, flagella or the glycocalyx (capsule)
used for adhering to receptors on specific host cells
Term
Streptococcus mutans
Definition
tooth decay
Term
Salmonella typhimurium
Definition
intestinal disease, gastroenteritis/diarrhea
Term
Bordetella pertussis
Definition
lung disease, whooping cough
Term
Escherichia coli
Definition
bladder infections
Term
Pseudomonas aeruginosa
Definition
biofilm infections
Term
Capsules (glycocalyx)
Definition
resists phagocytosis
A major virulence factor
Term
Cell wall components
Definition
chemical substances
Streptococcus pyogenes produces M protein
Term
coagulases
Definition
promote blood clotting
Term
kinases
Definition
dissolve clots
Term
hyaluronidase
Definition
hydrolyzes hyaluronic acid, a polysaccharide that holds cells together (especially in connective tissue)
Term
collagenase
Definition
hydrolyzes collagen which is the major protein in connective tissue
Term
IgA protease
Definition
destroy IgA antibodies
Term
Antigenic Variation
Definition
Some pathogens can alter their surface antigens - like changing pili composition
Remember: an antigen is anything that can elicit an immune response
Term
Invasins
Definition
rearrange the host cell cytoskeleton to “cradle” the bacterium into the cell - can lead to host signal transduction.
Term
Toxigenicity
Definition
capacity to produce toxins
May be transported by the blood
toxemia
Term
toxins Produce serious, and sometimes fatal, effects
Definition
Fever
Cardiovascular disturbances
Diarrhea
Shock
Inhibit protein synthesis
Damage eukaryotic cell membranes
Term
Intoxication
Definition
Exotoxins Found in both G+ and G- bacteria
Toxins secreted from the bacterial cell - into the extracellular fluid or into host tissues
Body produces antitoxins (antibodies) against the toxins
Term
CYTOXINS
Definition
Toxins that attack a variety of cell types
Term
Toxins that attack specific cell types named according to cell type or organ affected:
Definition
Neurotoxins - act on nervous tissue
Hepatotoxins – liver cells
Enterotoxins - act on enteric tissue (gut)
Cardiotoxins - act on cardiac tissue
Term
Type of bacterial species that produces them or for type of disease caused
Definition
diphtheria toxin (C. diphtheria), tetanus toxin (C. tetani), cholera toxin (V. cholera), botulinum toxin (C. botulinum
Term
plasmids and bacteriophages
Definition
Many toxins are carried on mobile DNA elements
Term
Type I toxins
Definition
bind to host cell surface,but do not enter cell. Ex., Superantigens
Term
Type II toxins
Definition
Act on host cell membranes and cause host cell lysis/death
Term
Type III toxins
Definition
A-B toxins, have a binding region (B) that binds specific host cell receptor (but does not enter host cell), and A portion (enzymatic portion) that enters host cell and exerts its toxic effect.
Term
Superantigens:
Definition
Hallmark - Force an unnatural fit between macrophages and T cells - causes an outpouring of cytokines that triggers SHOCK.
Term
Superantigen-mediated disease
Definition
- Fever, rash, desquamation, hypotension, shock, multiple organ failure
Term
Two types of Membrane Disrupting Toxins
Definition
Form channels in the membrane
Compromise the integrity of membrane phospholipids
Term
Endotoxin Production
Definition
part of G- bacterial cell wall
(ie. LPS in Gram- cell walls - lipid A is toxic portion)
released into tissues when the organisms die/lyse
weak toxins compared to exotoxins - but deadly in high concentrations - can cause shock
Term
Shock
Definition
Any life-threatening loss of blood pressure
Term
Septic shock
Definition
caused by bacteria in the blood.
(Toxins in the blood can also cause shock - toxemia)
Term
Systemic reaction
Definition
caused by high levels of bacteria or their products (LPS, LTA, peptidoglycan fragments) in bloodstream
Triggers complement activation, cytokine release, and coagulation cascade in body
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