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Virosphere

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refers to all places where viruses are found or interact with their hosts

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Tobacco Mosaic Disease

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Ivanowsky 1892; A viral disease causing tobacco leaves to shrivel and assume a mosaic appearance
> filtered the crushed leaves of a diseased plant and found the clear liquid passing through the filter contained the infectious agent.

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Foot and Mouth Disease

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A highly contagious viral disease of cloven-hoofed animals like sheep, cattle, and deer

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Yellow Fever

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A mosquito-borne viral disease of human liver and blood

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Bacteriophage/Phage

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A virus that infects and replicates within bacterial cells

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Virus

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An infectious agent consisting of DNA or RNA and surrounded by a protein sheath; in some cases, a membranous envelope surrounds the coat

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Virus

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small, obligate intracellular particles, most can be seen with an electron microscope, and must infect and take over a host cell in order to replicate because they lack the chemical machinery for generating energy and synthesizing large molecules

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Virus

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no organelles, no cytoplasm, no cell nucleus or nucleoid
> Composed of a nucleic acid core and a surrounding coat of protein

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Genome

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The complete set of genes in a virus or an organism
> contain either DNA or RNA (single or double stranded)
> usually folded or coiled, to keep small shape

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Capsid

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The protein coat that encloses the genome of a virus; gives shape or symmetry to the virus; two parts the capsomere and nucleocapsid; also provides protective covering for the viral genome

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Capsomere

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Any of the protein subunits of a capsid (the organization yields the viral symmetery)

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Nucleocapsid

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The combination of genome and capsid of a virus

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Spikes

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A protein projecting from the viral envelope or capsid that aids in attachment and penetration of a host cell
> help attach the virus to the host cell and facilitate penetration of the cell

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naked virus

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Viruses composed soley of a nucleocapsid

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Envelope

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The flexible membrane of protein and lipid that surrounds many types of viruses
> composed of lipids and proteins, similar to the host cell membrane, loose fitting structure over the nucleocapsid, many contain spikes projecting from the envelope

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enveloped viruses

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Viruses enclosed in an envelope

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Virion

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A completely assembled virus outside its host cell

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Helical

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One form of symmetry found in some viral capsids; helix tightly wound coil resembling a corkscrew or spring

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Icosahedral

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referring to a symmetrical figure composed of 20 triangular faces and 12 points; one of the forms of symmetry found in some viral capsids (e.g. herpes simplex, polioviruses)

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Complex

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referring to one form of symmetry found in some viral capsid; icosahedral + helical;

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Host Range

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The variety of species that a disease-causing microorganism can infect; refers to what organisms (hosts) the virus can infect and it is based on a virus’ capsid structure, most are very narrow

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Tissue Tropism

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refers to the specific tissues within a host that a virus infects (tissue attraction)

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DNA Viruses

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> either contain single stranded (ss) or double-stranded (ds)
> either linear or segmented
> replicated by direct DNA-to-DNA copying using DNA polymerase, which requires most DNA viruses to replicate in the host cell’s nucleus
* exception = poxviruses that replicate in the host cytoplasm, which means these viruses must carry the genes for their own DNA polymerase *

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RNA Viruses

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> either ssRNA or dsRNA genomes replicated by direct RNA-to-RNA copying
> either linear or segmented

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Positive Strand (+ Strand)

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referring to the RNA viruses whose genome consists of mRNA molecule; single-stranded, e.g. picornaviruses and coronaviruses

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Negative Strand (- Strand)

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referring to those RNA viruses whose genome cannot be directly transcribed into protein; RNA genomes consisting of RNA strands that would be complementary to a mRNA; single stranded, e.g. orthomyxoviruses and paramyxoviruses

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Retroviruses

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replicate indirectly through DNA intermediate (RNA-to-DNA-to-RNA) Each virion contains two copies of + strand RNA. During the infection process, a DNA intermediate will be formed using a reverse transcriptase enzyme carried within the virion

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Reverse Transcriptase

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An enzyme that copies single-stranded RNA into double stranded DNA
-RNA virus genomes are smaller than DNA virus genomes, and depend more heavily on host cell proteins and enzymes for replication

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Virus

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invades a living host cell, hijacks the metabolism of the cell to produce copies of itself, and often destroys the host cell when new virions are released

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Bacteriophages of the T-even group (T for type)

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they are large, complex, naked DNA virions with the characteristic head and tail of bacteriophage, contain tail fibers, which function like spikes on an animal virus and identify what bacterial species the phage will be able to infect; only carries a few of the many genes needed for viral synthesis and replication

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Virulent Viruses

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T-even phages, referring to a virus that can be extremely damaging when in the host

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Lytic Cycle

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A process by which a bacterial virus replicates within a host cell and ultimately destroys the host cell; Virulent Viruses

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Attachment Bacterial Viral Infection

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the phage and bacterial cells collide randomly, and if the tail fibers match with the receptor sites on the cell wall then this stage occurs. It consist of a weak chemical bond and in some cases, bacterial flagellum or pilus contain the receptor site

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Penetration Bacterial VIral Infection

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tail releases lyzosome, which dissolves part of the bacterial cell wall, the tail sheath contracts and the tail drives through the cell wall and when it reaches the cell membrane, DNA is ejected into the cytoplasm

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Biosynthesis Bacterial Viral Infection

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production of new phage genomes and capsid parts begin. The phage gene codes disrupt the host chromosome, so the phage DNA can use the bacterial nucleotides and enzymes to synthesize copies of its genome. Once mRNA transcribes the phage DNA, phage enzymes and capsid proteins begins. Ribosomes, amino acids, and enzymes are included in this process

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Maturation Bacterial Viral Infection

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phage parts assemble into complete virus particles, enzymes encoded by viral genes guide the assembly step-by-step, in the host cytoplasm phage heads and tail are assembled, another area heads are packaged with DNA, and tails are attached to the heads

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Release Bacterial Viral Infection

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mature phages burst from the ruptured bacterial shell, and are set free to infect more cell

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Lysogenic Cycle

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The events of a bacterial virus infection that result in the integration of its DNA into the bacterial chromosome

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Prophage

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The viral DNA of a bacterial virus that is inserted into the bacterial DNA and is passed on from one generation to the next during binary fission

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Temperate Phages

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Referring to a bacterial virus that enters a bacterial cell and then the viral DNA integrates into the bacterial cell’s chromosomes

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Productive Infection

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the active assembly and maturation of viruses in an animal cell

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Phage

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the bacterial cells survive the infection and continue to grow and divide normally, it undergoes DNA replication and binary fission, the ____ is copied and vertically transferred to chromosome, as cells divide, each daughter cell is “infected” containing the viral genome as a ____; the binary fissions can occur for an undefined time period, but at some point the cell becomes “stressed” (e.g. lack of nutrient, presence of noxious chemicals) and this triggers the ____ to excise itself from the bacterial chromosomes and switch to a lytic cycle, releasing the bacterial cells as new phages

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Attachment Animal Viruses

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Animal Viruses infect host cells by binding to receptors on the host cell’s plasma membrane by the spikes on the surface of the capsid or envelope, which determines the host range for a virus

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Penetration Animal Viruses

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Some viruses (adenoviruses like HIV) need a second receptor called the co-receptor for viral penetration into the cytoplasm, where they are taken into the cytoplasm as full nucleocapsids. Viruses like HIV the viral envelope fuses with the plasma membrane and releases the nucleocapsid into the cytoplasm

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Coreceptor

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the second receptor site where viral penetration into the cytoplasm takes place

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Penetration Animal Viruses

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Other viruses like adenoviruses and influenzavirus, the virion is taken into the cell by endocytosis. At the attachment site, the cell enfolds the virion within a vacuole and brings it into the cytoplasm, where it breaks down in the vacuole and releases the nucleocapsid or the genome into the cytoplasm

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Uncoating

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referring to the loss of a the viral capsid inside an infected eukaryotic cell

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Biosynthesis and Maturation Animal Viruses

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DNA of a DNA virus supplies the genetic codes for enzymes that synthesize viral parts from available building blocks; Most DNA viruses have the DNA genome synthesized in the host cell nucleus and capsid proteins are produced in the cytoplasm, the proteins are transported to the nucleus and join with the nuleic acid molecules for maturation (e.g Adenoviruses and herpesvirus)

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Biosynthesis and Maturation Animal Viruses

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RNA viruses the RNA immediately begins supplying the codes for protein synthesis as genome replication occurs because +ssRNA viruses act as a mRNA

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Biosynthesis and Maturation of Animal Viruses

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ssRNA viruses (e.g. influenzavirus) use their RNA as a template to synthesis a complementary (+) strand of RNA. An RNA dependent RNA polymerase is present in the virus to synthesize the (+) strand. The synthesized +ssRNA then is used as a mRNA molecule for protein synthesis as weel as a template to form –ssRNA genome

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Biosynthesis and Maturation of Animal Viruses

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The final steps of maturation include the acquisition of an envelope, where the envelope proteins (spikes) are synthesized and depending on the virus, incorporated into a nuclear or cytoplasmic membrane or the plasma membrane

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Release Animal viruses

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final stage where enveloped viruses either 1.) push through the plasma membrane forcing a portion of the membrane ahead of and around the virion resulting in an envelope 2.) a membrane-enclosed virus fuses with the plasma membrane releasing the virion (e.g. herpevirus) This is called budding need not necessarily kill the cell during release, but they leave the cell when the cell membrane ruptures

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Budding

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The controlled release of virus particles from an infected animal cell

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Latent Infection

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A viral infection where the viral DNA remains “dormant” within a host chromosome
> e.g. herpes simplex virus-1

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Latent Infection

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DNA virus can generate a productive or latent infection, In an infected sensory neuron, the virus under goes latency as the viral dsDNA enters the neuron’s cell nucleus and circularizes. No viral particles are produced for months or years until some stress reactivates the viral dsDNA and a productive infection is produced

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Reverse Transcriptase

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An enzyme that synthesizes a DNA molecule from the code supplied by an RNA molecule

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Provirus

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the viral DNA that has integrated into a eukaryotic host chromosome and is then passed on from one generation to the next through cell division

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Proviruses

answer

The dsDNA eneters the host cell nucleus and becomes integrated into the DNA of one chromosome, forming a _____ (e.g. retroviruses like HIV) which is then replicated each time the host cell divides along with the host genome, and is present in all progeny cells. _____ are protected from attack by antiretroviral drugs, but at any time can be reactivated and a productive infection occurs

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Koplik Spots

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red patches with white central lesions that form on the gums and walls of the pharynx during the early stages of measles

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River Postulates

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A set of procedures by which a specific virus can be associated with a specific disease

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River Postulates

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filtrates the infectious material isolated from the diseased host shown not to contain bacterial or other cultivatable organism must produce the same disease as found in the host or the filtrates must produce specific antibodies in appropriate animals

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Cytopathic Effect (CPE)

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Visible effect that can be seen in a virus infected host cell, which can be observed using a light microscope when examining cells obtained from body tissues or fluids

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Viruses

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change in cell structure often
> can have large number of lymphocytes with “foamy looking” highly vacuolated cytoplasm in infectious mononucleosis

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Syncytia

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A giant tissue cell formed by the fusion of cells infected with respiratory syncytial viruses (paramyxoviruses)

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Negri Bodies

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A cytoplasmic inclusion that occurs in brain cells infected with rabies vaccine

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Way to Culture Viruses

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inoculate them into fertilized chicken eggs by drilling a hole in the shell and a suspension of viral material is introduced
common with influenza viruses, which is origin of vaccine production

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Primary Cell Culture

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Animal cells separated from tissue and grown in cell culture; prepare the culture, animal cells are separated from a tissue with enzymes and suspended in a solution of nutrients, growth factors, pH buffers, and salts
> the cells adhere to the bottom of a plastic dish or well, and reproduce to form a monolayer

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Monolayer

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a single layer of cultured cells

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Cell Line

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A group of identical cells in culture and derived from a single cell; The different cell types in a primary cell culture can be separated enzymatically and isolated as a single cell type by this, and depends on the virus species to be cultivated in the monolayer and then viruses are introduced into culture

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Viruses

answer

can be detected by the formation of plaques in a monolayer

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Plaque

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A clear area on a lawn of bacterial cells where viruses have destroyed the bacterial cells; “bacterial lawn” or monolayer in animal cells; Viruses infect and replicate in the cells, and destroy the bacterial cells

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Phage Typing

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A procedure of using specific bacterial viruses to identify a particular strain of a bacterial species

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Cancer

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results from the uncontrolled reproduction (mitosis) of a single cell and the cells form a cluster of cells

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Tumor

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An abnormal uncontrolled growth of cells that has no physiological function

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Benign

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referring to a tumor that usually is not life threatening or likely to spread to another part of the body

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Metastasize

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referring to a tumor that spreads from the site of origin to other tissues in the body

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Malignant

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referring to a tumor that invades the tissue around it and may spread to other parts of the body

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Cancer

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A disease characterized by the radiating spread of malignant cells that reproduce at an uncontrolled rate

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Carcinogen

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Any physical or chemical substance that causes tumor formation

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Chemical Carcinogen

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hydrocarbons found in cigarettes smoke, asbestos, nickel, certain pestisides, and dyes, environmental pollutants in high amounts

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Physical Carcinogen

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UV light and X rays

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Sacroma

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A malignant tumor that begins growing in connective tissue such as muscle, bone, fat, or cartilage

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Burkitt lymphoma

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A tumor of the jaw triggered by the Epstein-Barr virus

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B Lymphocytes

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A white blood cell that matures into memory cells and plasma cells that secrete antibody

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Cervical Cancer

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Cancer of the cervix caused by several papillomaviruses

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PAP Smear

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A test to detect cancerous or precancerous cells of the cervix, allowing for early diagnosis of cancer

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Oncogenes

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A segement of DNA that can induce uncontrolled growth of a cell if permitted to function (genetic basis of cancer)

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Proto-Oncogenes

answer

A region of DNA in the chromosome of human cells; they are altered by carcinogens into oncogenes that transform cells; important in cell metabolism and growth regulation; influences cellular growth

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V-Oncogenes

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proto-oncogenes “captured” in the viral genome in the DNA; influences cellular growth

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Emerging Infectious Disease

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A new disease or changing disease that is seen for the first time (e.g. West Nile Virus, Hantavirus, HIV)

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Genetic Recombination

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The process of bring together different segments of DNA; allows the reassortment of genome segments (e.g swine flu)

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Mutation

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A permanent alteration of a DNA sequence
> When a single nucleotide is altered (point mutation) in an RNA virus genome in the host cytoplasm, because there is no way to “proofread” or correct the mistake during replication

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Viruses

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They need to find a suitable host to replicate and spread in
• Sometimes they make a species jump (e.g. from rodents to humans in South American hemorrhagic fevers); An increase in the size of the animal host population carrying a viral disease also can “explode” as an emerging viral disease

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Regressive Evolution Hypothesis

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Viruses are degenerate life-forms, they are derived from intracellular parasites that have lost many functions other organisms possess and have retained only those genes essential for their parasitic way of life

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Cellular Origin Hypothesis

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Viruses are derived from fragments of cellular genetic material and functional assemblies of macromolecules that have escaped their origins inside cells by being able to replicate autonomously in host

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Independent Entities Hypothesis

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Viruses coevolved with cellular organisms from the self-replicating molecules believed to have existed in the primitive prebiotic earth

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Virus Like Agents

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subviral particles that are disease agents

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Viroids

answer

An infectious RNA segment associated with certain plant diseases

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Dementia

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A loss of memory

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Transmissible Spongiform encephalopathies (TSEs)

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A group of progressive conditions that affect the brain and nervous system (e.g. Mad Cow Disease, Creutzfeldt-Jakob disease, scrapie in sheep and goats, wasting disease in elk and deer)

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Transmissible Spongiform Encephalopathies (TSEs)

answer

animal disease can be transmitted to other animals of the same species and possible to other animal species, including humans, and the disease causes the formation of “sponge like” holes in brain tissue

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Prion

answer

An infectious, self-replicating protein involved in human and animal diseases of the brain
> PrP is a coding gene expressed in the brain

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Protein Only Hypothesis

answer

The idea that prions are composed solely of protein and contain no nucleic acid; two types of prion proteins: 1.) normal cellular prions (PrPc) found on the surfaces of brain cells 2.) abnormal, misfolded prions (PrPSC) have a different shpe, and are suspected infectious agents of neurological diseases (TSEs) like mad cow disease and scrapie

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Prion Diseases or TSEs

answer

spread by infectious PrPSC binding to normal PrpPC causing the normal PrP to change shape, which snowball effects by turning more and more normal PrP to abnormal

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Variant CJD (vCJD)

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a new form of Creutzfeldt Jakob Disease (CJD) that shows similarities between the animal TSEs

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