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electrophoresis

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a technique that involves separating molecules based on their electrical charge, size, and shape

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gel electrophoresis

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DNA molecules have an overall negative charge are drawn through a semisolid gel (agarose) by an electrical current toward the positive electrode in an electrophoresis chamber. smaller fragments travel faster and further.

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DNA microarray

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consists of ssDNA, either genetic DNA or cDNA, immobilized on glass slides, silicon chips, or nylon membranes.
purpose: monitoring gene expression, diagnosing infection, identifying organisms in an environmental sample

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electroporation

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involves using an electral current to puncture microscopic holes through a cell's membrane so that DNA can enter from the environment. can be used on all types of cells.

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protoplast

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cells that have had their cell walls enzymatically removed

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protoplast fusion

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when protoplasts encounter one another, their cytoplasmic membrane's may fuse to form a single cell that contains the genomes of both "parent" cells. exposure to polyethylene glycol increases the rate of fusion. the DNA from the two fused cells recombines to form a recombinant molecule. often used for genetic modification of plants.

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injection (inserting DNA)

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two types of injection: gene gun & microinjection. injection can be used on intact tissues such as in plant seeds.

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gene gun

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0.22-caliber cartridge or compressed gas powers the firing of tiny tungsten or gold beads covered with DNA into a target cell. the cell eventually eliminates the inert metal beads.

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microinjection

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DNA is inserted into a target cell with a glass micropipette having a tip diameter smaller than that of the cell or nucleus.

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DNA fingerprinting

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identifying individuals or organisms by their unique DNA sequences. any given sequence is a unique pattern and must be compared to patterns produced from other DNA molecules. genetic fingerprinting can be used to determine paternity, for forensics, and also for identifying pathogens.

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virus

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acellular, miniscule, infectious agent usually having one or more pieces of nucleic acid- either RNA or DNA. they lack cytoplasmic membranes, cytosol, functional organelles. not cappable of metabolic activity on their own; must invade cells and take over the host cell's metabolic machinery

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virion

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a virus outside of the cell, in the extracellular state. consists of a capsid surrounding the nucleic acid, together called the nucleocapsid. some virions have an envelope surrounding the nucleocapsid.

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capsid

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protein coat surrounding nucleic acid core

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nucleocapsid

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the nucleic acid and its capsid, together

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envelope

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phospholipid membrane surrounding a viral nucleocapsid. consists of phospholipid bilayer and proteins. some have glycoproteins appearing as spikes. proteins and glycoproteins play a role in host recognition.

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generalists

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viruses that are capable of infecting may kinds of cells in many types of hosts

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bacteriophage

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virus that infects bacteria. aka phage.

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capsomeres

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proteinaceous subunits of a capsid

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helical virus

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virus composed of capsomeres that bond together in a spiral fashion to form a tube around the nucleic acid

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polyhedral virus

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viral capsid is roughly spherical, with a similar shape to a geodesic dome. most common type is an icosahedron, which has 20 sides.

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complex virus

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capsids of many different shapes that do not fit into either of the other viral shape categories.

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matrix proteins

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viral proteins that fill the region between the envelope and the capsid

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ICTV

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International Committee on Taxonomy of Viruses, established in 1966 to provide a single taxonomic scheme for viral classification and identification

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lytic replication cycle

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process of viral replication consisting of five stages ending with lysis of and release of new virions from the host cell. includes 5 stages: attachment, entry, synthesis, assembly, and release.

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attachment (viral replication)

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1st stage of viral replication. dependent upon the chemical attraction and precise fit between attachment proteins and complimentary receptor proteins on the surface of the host's cell wall

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entry (viral replication)

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2nd stage of viral replication. phage releases lysozyme, a protein enzyme carried within the capsid that weakens the peptidoglycan of the cell wall. the phage injects its genome into the bacterium.

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synthesis (viral replication)

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3rd stage of lytic replication and 5th stage of lysogenic replication: after entry, viral enzymes degrade the bacterial DNA into consituent nucleotides. the bacterium stops making its own molecules and begins synthesizing new viruses.

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assembly (viral replication)

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4th stage of lytic replication and 6th stage of lysogenic replication: as capsomeres accumulate within the cell, they spontaneously attach to one another to form new capsid heads. then tails assemble and attach to heads, forming mature virions. requires little to no enzymatic activity.

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release (viral replication)

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newly assembled virions are released from the cell as lysozyme completes its work on the cell wall and the bacterium disintegrates.

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burst time

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the period of time required to complete the entire process of lytic viral replication, from attachment to release.

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burst size

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the number of new virions released from each lysed bacterial cell

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lysogenic replication cycle

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modified viral replication cycle in which the bacteriophage enters a bacterial cell, inserts itself into the host DNA, and remains inactive. the phage is then replicated every time the host cell replicates its chromosome. later, the phage may lyse.

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temperate phage

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aka lysogenic phage. bacteriophage that does not immediately kill its host but replicates through lysogeny

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prophage

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an inactive bacteriophage, which is inserted into a host's chromosome

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latency (viral replication)

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3rd stage of lysogenic replication. once phage enter's the bacterium and inserts itself into the host DNA, the prophage remains inactive.

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lysogenic conversion

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lysogenic phages can change the phenotype of a bacterium, for example from a harmless form to a pathogen.
bacteriophage genes are responsible for toxins and other disease-evoking proteins found in cholera, diptheria and rhuematic fever.

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induction

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4th stage of lysogenic replication. process whereby the prophage is esxcised from the host chromosome. inductive agents are typically the same chemical and physical agents that damage DNA molecules such as UV light, x-rays, and carcinogenic chemicals

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attachment of animal viruses

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animal viruses lack both heads and tail fibers. instead, they typically have glycoprotein spikes or other attachment molecules on their capsids or envelopes.

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entry of animal viruses

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3 different mechanisms: direct penetration, membrane fusion, and endocytosis.

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direct penetration

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method of entry for animal viruses. process in which the viral capsid attaches and sinks into the cytoplasmic membrane, creating a pore trhough which the genome alone enters the cell. ie, poliovirus

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membrane fusion

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method of entry for animal viruses. the viral envelope and the host cell membrane fuse together, releasing the capsid into the cell chromosome. ie, measles and AIDs virus.

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endocytosis

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most enveloped animal viruses and some naked animal viruses enter host cells by triggering endocytosis. attachment of the animal virus to receptor molecule's on the cell's surface stimulates the cell to endocytize the entire virus. ie, adenovirus and herpes virus.

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uncoating

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the removal of a viral capsid within the host cell (for animal viruses that enter the host cell with their capsid intact)

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synthesis of animal viruses

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each type of animal virus requires a different strategy for synthesis depending upon the kind of nucleic acid involved

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dsDNA: animal virus synthesis

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cellular enzymes replicate the viral genome in the same manner as they replicate host dsDNA, using each strand of the viral DNA as a template for its complement

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ssDNA: animal virus synthesis

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when a parovirus enters the nucleus of a cell, host enzymes produce a new strand of DNA complementary to the viral genome which then binds to form dsDNA. transcription of mRNA, replication of new ssDNA, and viral assembly then follow the DNA virus pattern.

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parvovirus

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a human virus composed of ssDNA

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+ssRNA: animal virus synthesis

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single stranded viral RNA that can act directly as mRNA; ribosomoes translate polypeptides using the codons of the viral genome. a complimentary -ssRNA strand is transcribed by viral RNA transcriptase in order to be used as the template for more +ssRNA

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retroviruses: animal virus synthesis

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ssRNA viruses that do not use their genomes as mRNA but instead use reverse transcriptase to transcribe the viral genome into intermediary DNA. the DNA then acts as the template for +RNA molecules, which act as both mRNA and also as genomes for new virions

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-ssRNA: animal virus synthesis

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-RNA is not recognized by ribosomes. virus must carry "RNA-dependent RNA transcriptase" within its capsid and release into the host cytoplasm during uncoating. RNA-dependent RNA transcriptase transcribes +RNA from the virus' -RNA genome. the +RNA will act as the mRNA as well as the template for transcription of more -RNA viral copies.

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dsRNA: animal virus synthesis

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the positive strand of genome serves as mRNA for the translation of proteins, one of which is RNA polymerase that transcribes dsRNA. each strand acts as a template for transcription of its opposite.

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assembly of animal viruses

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most DNA viruses assemble in and are released from the nucleus into the cytosol. most RNA viruses develop solely in the cytoplasm.

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release of animal viruses

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enveloped viruses are released via a process called budding- assembled virions are extruded through cell membranes acquiring a portion of the membrane which becomes the viral envelope. naked animal viruses may be released via exocytosis or they may cause lysis and death of the host cell.

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persistent infections

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infections with enveloped viruses in which host cells shed viruses slowly and relatively steadily

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latency

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some animal viruses can remain dormant in cells. some viruses do incorporate their genome into the host chromosome while others do not.

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proviruses

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aka latent viruses.. viruses involved in latency

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neoplasia

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phenomenon of uncontrolled cell division in a multicellular animal

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tumor

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mass of neoplastic cells

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beign

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tumors which remain in one place and are not generally harmful

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malignant

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tumors that invade neighboring tissues and even travel throughout the body to invade other organs and tissues to produce new tumors

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metastasis

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spreading of malignant cancer cells to nonadjacent organs and tissues, where they produce new tumors

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cancer

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disease characterized by the presence of one or more malignant tumors

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protooncogenes

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genes that play a role in cell division. normally repressed.

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oncogenes

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active protooncogenes. activity of oncogenes or inactivation of oncogene repressors can cause cancer to develop.

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viral cancers

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20-25% of human cnacers are caused by viruses. examples include- Burkitt's lymphoma, Hodgkin's disease, Karposi's sarcoma, and cervical cancer

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plaques

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in phage typing, the clear regions within the bacterial lawn where growth is inhibited by bacteriophages

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plaque assay

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technique for estimating phage numbers in which each plaque corresponds to a single phage in the original bacterium/virus mixture

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cell culture

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cells isolated from an organism and grown on the surface of a medium or in broth. viruses can be grown in a cell culture.

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diploid cell culture

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type of cell culture created from embryonic animal, plant, or human cells that have been isolated and provided appropriate growth conditions

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continuous cell cultures

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type of cell culture created from tumor cells; longer lasting

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viroids

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extremely small, circular piece of RNA that is infectious and pathogenic in plants

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prions

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proteinaceous infectious particle that lacks nucleic acids and replicates by converting similar normal proteins into new prions.

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chemotherapeutic agents

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drugs that act against diseases

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antibiotics

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anitmicrobial agents that are produced naturally by an organism

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semisynthetics

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chemically altered antibiotics

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selective toxicity

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prniciple by which an effective antimicrobial agent must be more toxic to a pathogen than to the pathogen's host

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