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Filebox - Biotechnology Dictionary Category: Earth and Environment > Biotechnology Date & country: 13/09/2007, USA Words: 455

Physical map
A map showing physical locations on a DNA molecule, such as restriction sites, and sequence-tagged sites. (See Mapping.)

Plant Pest Act (PPA)
See U.S. Department of Agriculture.

Plant Variety Act (PVA)
See U.S. Department of Agriculture.

Plaque
A clear spot on a lawn of bacteria or cultured cells where cells have been Iysed by viral infection.

Plasmid (p)
A circular DNA molecule, capable of autonomous replication, which typically carries one or more genes encoding antibiotic resistance proteins. Plasmids can transfer genes between bacteria and are important tools of transformation for genetic engineers. (See Nicked circle, pAMP, Relaxed plasmid, Stringent plasmid, Supercoiled plasmid.)

Pleiotrophy
The effect of a particular gene on several different traits.

Point mutation
A change in a single base pair of a DNA sequence in a gene. (See Mutation.)

Poly(A) polymerase
Catalyzes the addition of adenine residues to the 3' end of pre-mRNAs to form the poly(A) tail. (See Polymerase.)

Polyacrylamide gel electrophoresis
Electrophoresis through a matrix composed of a synthetic polymer, used to separate proteins, small DNA, or RNA molecules of up to 1000 nucleotides. Used in DNA sequencing. (See Electrophoresis.)

Polyclonal antibodies
A mixture of immunoglobulin molecules secreted against a specific antigen, each recognizing a different epitope.

Polygenic
Controlled by or associated with more than one gene.

Polylinker
A short DNA sequence containing several re- striction enzyme recognition sites that is contained in cloning vectors.

Polymer
A molecule composed of repeated subunits.

Polymerase (DNA)
Synthesizes a double-stranded DNA molecule using a primer and DNA as a template. (See Poly(A) polymerase, Polymerase chain reaction, RNA polymerase, Taq polymerase.)

polymerase chain reaction (PCR)
A procedure that en- zymatically amplifies a DNA polymerase. (See Polymerase.)

Polymorphisms
Variant forms of a particular gene that occur simultaneously in a population.

Polynucleotide
A DNA polymer composed of multiple nucleotides. (See Nucleotide.)

Polypeptide (protein)
A polymer composed of multiple amino acid units linked by peptide bonds.

Polyploid
A multiple of the haploid chromosome number that results from chromosome replication without nuclear division.

Polysaccharide
A polymer composed of multiple units of monosaccharide (simple sugar).

Polyvalent vaccine
A recombinant organism into which has been cloned antigenic determinants from a number of different disease-causing organisms. (See Vaccine.)

Population
A local group of organisms belonging to the same species and capable of interbreeding.

PPA
See U.S. Department of Agriculture.

Primary cell
A cell or cell line taken directly from a living organism, which is not immortalized.

Primer
A short DNA or RNA fragment annealed to single-stranded DNA, from which DNA polymerase extends a new DNA strand to produce a duplex molecule.

Prion
See Proteinaceous infectious particle.

Probe
A sequence of DNA or RNA, labeled or marked with a radioactive isotope, used to detect the presence of complementary nucleotide sequences. See Nucleotide.

Probe
A single-stranded DNA that has been radioactively labeled and is used to identify complementary sequences in genes or DNA fragments of interest. (See Multilocus probe.)

Prokaryote
A bacterial cell lacking a true nucleus; its DNA is usually in one long strand. See Eukaryote.

Promoter
A region of DNA extending 150-300 bp upstream from the transcription start site that contains binding sites for RNA polymerase and a number of proteins that regulate the rate of transcription of the adjacent gene. (See Constitutive promoter.)

Pronucleus
Either of the two haploid gamete nuclei just prior to their fusion in the fertilized ovum.

Protease
An enzyme that cleaves peptide bonds that link amino acids in protein molecules.

Protein
A polymer of amino acids linked via peptide bonds and which may be composed of two or more polypeptide chains. (See Polypeptide.)

Protein kinase
An enzyme that adds phosphate groups to a protein molecule at serine, threonine, or tyrosine residues.

Proteolytic
The ability to break down protein molecules.

Proto-oncogene
See oncogene.

Provirus
See virus.

Public Health Service Act
See Food and Drug Administration.

pUC
A widely used expression plasmid containing a -galactosidase gene. (See Plasmid.)

PVA
The Plant Variety Act. See U.S. Department of Agriculture.

Reading frame
A series of triplet codons beginning from a specific nucleotide. Depending on where one begins, each DNA strand contains three different reading frames. (See Open reading frame, Overlapping reading frames.)

Recessive gene
Characterized as having a phenotype expressed only when both copies of the gene are mutated or missing.

Recognition sequence (site)
A nucleotide sequence--composed typically of 4, 6, or 8 nucleotides--that is recognized by a restriction endonuclease. Type II enzyrnes cut (and their corresponding modification enzymes methylate) within or very near the recognition sequence.

Recombinant
A cell that results from recombination of genes.

Recombinant DNA
The process of cutting and recombining DNA fragments from different sources as a means to isolate genes or to alter their structure and function.

Recombination frequency
The frequency at which crossing over occurs between two chromosomal loci--the probability that two loci will become unlinked during meiosis.

Regulatory gene
A gene whose protein controls the activity of other genes or metabolic pathways.

Relaxed circle plasmid
See Plasmid.

Relaxed plasmid
A plasmid that replicates independently of the main bacterial chromosome and is present in 10-500 copies per cell. (See Plasmid.)

Renature
The reannealing (hydrogen bonding) of single- stranded DNA and/or RNA to form a duplex molecule.

Replicon
A chromosomal region containing the DNA sequences necessary to initiate DNA replication processes.

Repressor
A DNA-binding protein in prokaryotes that blocks gene transcription by binding to the operator.

Restriction endonuclease (enzyme)
A class of endonucleases that cleaves DNA after recognizing a specific sequence, such as BamH1 (GGATCC), EcoRI (GAATTC), and HindIII (AAGCTT). Type I. Cuts nonspecifically a distance greater than 1000 bp from its recognition sequence and contains both restriction and methylation activities. Type II. Cuts at or near a short, and often symmetrical, recognition sequence. A separate enzyme methylates the same recognition sequence. Type III. Cuts 24-26 bp downstream from a short, asymmetrical recogni…

Restriction map
See Mapping.

Retrovirus
A member of a class of RNA viruses that utilizes the enzyme reverse transcriptase to reverse copy its genome into a DNA intermediate, which integrates into the hostcell chromosome. Many naturally occurring cancers of vertebrate animals are caused by retroviruses.

Reverse genetics
Using linkage analysis and polymorphic markers to isolate a disease gene in the absence of a known metabolic defect, then using the DNA sequence of the cloned gene to predict the amino acid sequence of its encoded protein.

RFLP
See Restriction-fragment-length polymorphism.

Rhizobia
Bacteria in a symbiotic relationship with leguminous plants that results in nitrogen fixation. See Nitrogen fixation.

Rhizosphere
The soils region on and around plant roots.

Ribosomal RNA (rRNA)
The RNA component of the ribosome. (See RNA.)

Ribosome
Cellular organelle that is the site of protein synthesis during translation. See Organelle, Translation.

Ribosome-binding site
The region of an mRNA molecule that binds the ribosome to initiate translation.

Ribozyme
See Catalytic RNA.

RNA (ribonucleic acid)
An organic acid composed of re- peating nucleotide units of adenine, guanine, cytosine, and uracil, whose ribose components are linked by phosphodiester bonds. (See Antisense RNA, Heterogeneous nuclear RNA, Messenger RNA, Ribosomal RNA, RNA polymerase, Small nuclear RNA, Transfer RNA.)

RNA polymerase
Transcribes RNA from a DNA template. (See Polymerase, RNA.)

rRNA
See Ribosomal RNA.

Salmonella
A genus of rod-shaped, gram-negative bacteria that are a common cause of food poisoning.

Satellite RNA (viroids)
A small, self-splicing RNA molecule that accompanies several plant viruses, including tobacco ringspot virus.

Selectable marker
A gene whose expression allows one to identify cells that have been transforrned or transfected with a vector containing the marker gene. (See B-Lactamase, Kanr.)

Self-pollination
Pollen of one plant is transferred to the female part of the same plant or another plant with the same genetic makeup.

Semiconservative replication
During DNA duplication, each strand of a parent DNA molecule is a template for the synthesis of its new complementary strand. Thus, one half of a preexisting DNA molecule is conserved during each round of replication.

Sequence hypothesis
Francis Crick's seminal concept that genetic information exists as a linear DNA code; DNA and protein sequence are colinear

Sequence-tagged site (STS)
A unique (single-copy) DNA sequence used as a mapping landmark on a chromosome.

Sexual reproduction
The process where two cells (gametes) fuse to form one hybrid, fertilized cell. See Asexual reproduction, Gamete, Hybrid.

Signal transduction
The biochemical events that conduct the signal of a hormone or growth factor from the cell exterior, through the cell membrane, and into the cytoplasm. This involves a number of molecules, including receptors, pro- teins, and messengers.

Site-directed mutagenesis
The process of introducing spe- cific base-pair mutations into a gene.

Small nuclear RNA (snRNA)
Short RNA transcripts of 100-300 bp that associate with proteins to form small nuclear ribonucleoprotein particles (snRNPs), which participate in RNA processing. (See RNA.)

snRNA
See Small nuclear RNA.

Somatic cell
Any nongerm cell that composes the body of an organism and which possesses a set of multiploid chromosomes (diploid in most organisms). (See Gamete, Somatic cell gene therapy.)

Somatic cell gene therapy
The repair or replacement of a defective gene within somatic tissue. (See Somatic cell.)

Somatotrophin
See Human growth hormone.

Southern blotting
See Southern hybridization.

Species
A classification of related organisms that can freely interbreed.

Spore
A form taken by certain microbes that enables them to exist in a dormant stage. It is an asexual reproductive cell. See Asexual reproduction, Dormant.

Stationary phase
The plateau of the growth curve after log growth, during which cell number remains constant. New cells are produced at the same rate as older cells die. (See Growth phase.)

Sticky end
A protruding, single-stranded nucleotide se- quence produced when a restriction endonuclease cleaves off center in its recognition sequence.

Stop codon
See Termination codon.

Stringency
Reaction conditions--notably temperature, salt, and pH--that dictate the annealing of single-stranded DNA/DNA, DNA/RNA, and RNA/RNA hybrids. At high stringency, duplexes form only between strands with perfect one-to-one complementarity; lower stringency allows annealing between strands with some degree of mismatch between bases.

Stringent plasmid
A plasmid that only replicates along with the main bacterial chromosome and is present as a single copy, or at most several copies, per cell. (See plasmid.)

Structure-functionalism
The scientific tradition that stresses the relationship between a physical structure and its function, for example, the related disciplines of anatomy and physiology.

STS
See Sequence-tagged site.

Subcloning
The process of tranferring a cloned DNA fragment from one vector to another. (See Cloning.)

Subunit vaccine
A vaccine composed of a purified antigenic determinant that is separated from the virulent organism. (See Vaccine, Enzyme.)

Supercoiled plasmid
The predominant in vivo form of plasmid, in which the plasmid is coiled around histone-like proteins. Supporting proteins are stripped away during extraction from the bacterial cell, causing the plasmid molecule to supercoil around itself in vitro. (See Plasmid.)

Supergene
A group of neighboring genes on a chromosome that tend to be inherited together and sometimes are functionally related.

Supernatant
The soluble liquid &action of a sample after centrifugation or precipitation of insoluble solids.

Symbiosis
The close association of two or more dissimilar organisms where both receive an advantage from the association. See Commensalism, Parasitism.

Synapsis
The pairing of homologous chromosome pairs during prophase of the first meiotic division, when crossing over occurs.

T-DNA (transfer DNA, tumor-DNA)
The transforming region of DNA in the Ti plasmid of Agrobacterium tumefaciens.

Taq polymerase
A heat-stable DNA polymerase isolated from the bacterium Therrnus aquaticus, used in PCR. (See Polymerase.)