unit 8 (acellular pathogens) Flashcards
(110 cards)
1
Q
characteristics of viruses
A
infectious acellular pathogens, obligate intracellular parasites w/ host and cell type specificity, DNA or RNA genome, genome surrounded by protein capsid
2
Q
types of host cells that viruses can infect
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every type of host cell (plants, animals, fungi, protists, bacteria, archaea)
3
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host range definition
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the host cells that viruses can infect, viruses are only able to infect the cells of one or a few species of an organism
4
Q
host range determined by
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certain specific surface receptors on host cells that viruses can attach to
5
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virus transmission modes
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direct and indirect contact, mechanical and biological vectors
6
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size range of viruses
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20-900 nm
7
Q
genetic material of viruses
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either DNA or RNA, never both
8
Q
capsid definition
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protein coat that surrounds the viral genome and enzymes needed to direct the synthesis of new virions
9
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capsomere definition
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protein subunits that make up a capsid, made of one or more different types of capsomere proteins that interlock to form the closely packed capsid
10
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naked viruses (nonenveloped viruses) definition
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viruses formed only with nucleic acid and capsid
11
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enveloped virus definition
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viruses formed w/ a nucleic acid packed capsid surrounded by a lipid layer
12
Q
viral envelope definition
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small portion of phospholipid membrane obtained as the virion buds from the host cell.
13
Q
spikes definition
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protein structures that extend outward and away from the capsid on some naked and enveloped viruses
14
Q
spike function
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allow the virus to attach and enter a cell
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Q
spike protein examples
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influenza virus spikes hemagglutinin (H) and neuraminidase (N)
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capsid shape types
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helical, polyhedral, or complex
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helical capsid
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capsid is cylindrical or rod shaped, with the genome fitting just inside the length of the capsid
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polyhedral capsids
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consist of nucleic acid surrounded by a many sided capsid in the form of an icosahedron
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icosahedral capsid
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3D, 20 sided structure that resembles a soccer ball
20
Q
complex capsid
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have features of both polyhedral and helical viruses
21
Q
what does the International committee on taxonomy of viruses (ICTV) do?
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develops, refines, and maintains a universal taxonomy of viruses
22
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viruses are classified into
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families and genera\
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viruses are classified based on
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viral genetics, morphology, chemistry, and mechanism of multiplication
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Q
viral family names end in
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-viridae
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viral genus names end in
-virus
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lytic animal virus infection stages
attachment, entry and uncoating, transcription, replication of viral DNA and proteins, assembly, and release
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animal viruses enter the host cell by
endocytosis or membrane fusion
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endocytosis definition
engulfment by host cell
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membrane fusion definition
fusion of viral envelope w/ host membrane
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tissue tropism definition
most viruses only infect certain types of cells within tissues
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attachment (lytic animal virus)
virus become attached to target cell by binding to specific host cell receptors w/ viral glycoproteins (spike proteins)
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entry and uncoating (lytic animal virus)
the host cell engulfs the virus by endocytosis, the viral capsid and envelope are digested as it enters the cell, uncoating the viral enzymes and genetic material
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transcription (lytic animal virus)
viral DNA enters host cell nucleus, where it is transcribed by viral RNA polymerase to create mRNA
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replication of viral DNA and proteins (lytic animal virus)
transcription of viral DNA by RNA polymerase creates mRNA which is read by a ribosome to synthesize viral proteins. viral DNA is replicated.
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assembly (lytic animal virus)
new phage particles are assemble using viral proteins and DNA that were replicated
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release (lytic animal virus)
new viral particles that were made are released into extracellular fluid, allowing them to infect new cells. The host cell is not killed by this and continues to produce new virions
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types of nature of viral genome in viruses
dsDNA, ssDNA, ssRNA, dsRNA
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three types of RNA genome
dsRNA, +ssRNA, -ssRNA
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if a virus contains +ssRNA genome
it acts as cellular mRNA and can be translated directly to make viral proteins
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if a virus contains -ssRNA genome
host ribosomes cannot translate it until the -ssRNA is replicated into +ssRNA by viral RNA-dependent RNA polymerase
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retrovirus definition
+ssRNA viruses that carry reverse transcriptase
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retrovirus replication cycle stages
attachment, entry and uncoating, synthesis of dsDNA by reverse transcriptase, integration, synthesis of viral RNAs, synthesis of viral proteins, assembly and maturation, release, replicating cells w/ latent virus
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provirus definition
integrated viral genome in host genome that can remain in the host for a long time (latency) and does not excise from the host genome
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retrovirus example
HIV
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attachment (HIV retrovirus)
HIV fuses to host cell surface. HIV binds to the CD4 receptors on helper T cells, which allows the secondary binding of chemokine coreceptor to the viral envelope
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entry and uncoating (HIV retrovirus)
HIV and host membrane fuse and viral genetic material enters the cell while the envelope is left at the surface. HIV's matrix and capsid protein are digested as it enters the cell, releasing viral enzymes and viral RNA
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synthesis of dsDNA by reverse transcriptase (HIV retrovirus)
reverse transcriptase uses host nucleotides to convert viral RNA to DNA. the single stranded DNA is reverse transcribed again to create dsDNA
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integration (HIV retrovirus)
integrase, an enzyme that entered the cell w/ the virus, carries the dsDNA into the nucleus through a nuclear pore. integrase then nicks the host chromosome, allowing the HIV DNA to insert itself into the host chromosome.
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synthesis of viral RNAs (HIV retrovirus)
new viral RNA is synthesized when RNA polymerase transcribes the section of the chromosome that contains the viral DNA
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synthesis of viral proteins (HIV retrovirus)
new viral RNA is used as genomic RNA and to make viral proteins. the mRNA of viral DNA is translated by ribosome and the viral proteins are created
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assembly and maturation (HIV retrovirus)
the viral proteins get taken to the cell's surface where they get embedded into the cell membrane, forming new immature HIV virus
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release (HIV retrovirus)
once a new immature HIV virus forms, it buds off, taking the host cell's membrane and using it as an envelope. Mature virions form when proteases break down the polyproteins chains in the virion
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replicating cells with latent virus (HIV retrovirus)
latent virus is replicated when host cells divide, creating another infected cell with the potential to create new virions and infect other cells
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persistent infection definition
occurs when a virus is not completely cleared from the system of the host but stays in certain tissues or organs of the infected person
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effects of persistent viruses
virus may remain silent or undergo productive infection without seriously harming or killing the host
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mechanisms of persistent infection
involve regulation of viral or host gene expressions or the alteration of host immune response
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primary categories of persistent infections
latent infection and chronic infection
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examples of latent viruses
herpes simplex virus, varicella-zoster virus, Epstein-Barr virus
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examples of chronic viruses
hepatitis C and HIV
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latent virus definition
viruses that are capable at remaining hidden or dormant inside a cell
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chronic infection definition
disease w/ symptoms that are recurrent or persistent over a long time
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mechanisms by which HIV maintains chronic persistence
prevention of viral antigens of the surface of infected cells, altering immune cells themselves, restricting expression of viral genes, and rapidly changing viral antigens through mutation
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viral growth curve stages
inoculation, eclipse, burst, burst size
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inoculum stage
inoculum of virus causes infection, binding to cells
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eclipse stage
viruses bind and penetrate the cells, no virions detected in the medium
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burst stage
virions are released and lysed from the host cell at the same time
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burst size stage
number of virions released per bacterium
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one-step multiplication curve for bacteriophage
host cells lyse, releasing many viral particles into the medium, which leads to a very steep rise in viral titer
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Viral titer definition
number of virions per unit volume
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viroids consist of
a short strand of circular RNA capable of self-replication
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viroid replication
take control of host machinery to replicate their RNA genome
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do viroids have capsids?
viroids do not have a protein coat to protect their genetic information
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viroid diseases examples
agriculture diseases: potato tuber spindle disease
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virusoid definition
subviral particles, best described as non-self replicating ssRNAs
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virusoid replication
like viroids, but require the cell be infected w/ a specific "helper" virus.
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helper virus function for virusoid
helper virus enters host cell and released virusoids which replicates its RNA independently from the helper virus
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helper virus example
subterranean clover mottle virus
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prion definition
misfolded rogue form of a normal protein found in the cell that can stimulate other endogenous normal proteins to become misfolded, forming plaques
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prion formation caused by
genetic mutation or occurs spontaneously
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plaques
large aggregates of prions
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disease caused by prions
transmissible spongiform encephalopathy
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TSE transmission
eating contaminated meat, heredity, by contact w/ contaminated tissue
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viral virulence factors examples
adhesions, antigenic variation
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viral adhesion examples
spike protein hemagglutinin, glycoprotein gp120
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hemagglutinin functioning
allows influenza virus to bind to sialic acid on the membrane of host respiratory and intestinal cells
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gp120 functioning
allows HIV to attach to helper T cell through interaction w/ CD4 receptor and chemokine coreceptor
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types of antigenic variation
antigenic drift, antigenic shift
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antigenic drift definition
result of point mutations causing slight changes in the spike proteins hemagglutinin and neuraminidase
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antigenic shift definition
major change in spike proteins due to gene reassortment, which typically occurs when two different flu viruses infect the same host cell
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antigenic variation results in
continual emergence of new strains that the immune system will not recognize
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cellular components that help us identify an organism
sequence of a DNA molecule when compared to known sequences housed in a database, comparing protein signatures
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molecular analysis of DNA methods
nucleic acid probing, agarose gel electrophoresis, restriction fragment length polymorphism (RFLP) analysis, southern blots and modifications, and microarray analysis
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nucleic acid probing tests for/how
identifies the presences of a certain DNA sequence using artificially constructed DNA probes that complementary bind to the certain DNA sequence
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what do agarose gel electrophoresis tests do
physically separate DNA fragments of different sizes and compared to known size fragments of DNA ladder, which can identify the individual or species to which the DNA belongs
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how do agarose gel electrophoresis test work
DNA samples w/ colored dye are put into wells. negative electrode is placed near the DNA, positive electrode opposite DNA. DNA has a negative charge and will be drawn to the positive electrode, smaller DNA molecules will travel through the gel faster. DNA ladder that has known size of fragments is used to determine the sizes of other samples
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what do restriction fragment length polymorphism tests do?
allows for the visualization by agarose gel electrophoresis of distinct variants of a DNA sequence caused by differences in restriction sites
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southern blot
allows researchers to find a particular DNA sequence within an sample
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northern blot
allows researchers to detect a particular mRNA sequence expressed in a sample
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microarray technology
a nucleic acid hybridization technique that allows for the examination of many thousands of genes at once to find differences in genes or gene expression patterns between two samples
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polyacrylamide gel electrophoresis (PAGE)
separates proteins based on their charges and/or their size using process similar to agarose gel electrophoresis
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primers function
DNA replication requires the use of DNA primers for the initiation of replication in PCR
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polymerase chain reaction (PCR) function
allows for rapid amplification of specific DNA sequence
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PCR steps
denaturation, annealing, and extension
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denaturation (PCR step)
dsDNA containing the target sequence is denatured at 95 degrees
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annealing (PCR step)
temp is lowered to 50 degrees to allow DNA primers complementary to the ends of the target sequence to anneal to the template strands, with one primer annealing to each strand
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extension (PCR step)
temp is raised to 72 degrees, optimal temp for DNA polymerase, allowing for the addition of nucleotides to the primer using the single-stranded target as template
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PCR cycles yield
double the number of dsDNA target strands, cycle is run 25-40 times
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reverse transcriptase PCR function
used to detect mRNA expression
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real-time PCR function
quantifies a particular sequence in the original sample
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next generation sequencing function
allow for rapid and inexpensive sequencing of the genomes of many organims,
