Bacteriophage, or phage -- A virus that infects and lyses certain bacteria, such as E. Coli. Bacteriophages were discovered by Felix d'Herelle and Frederick Twort in the 1910s. In the 1940s, Max Delbruck encouraged the phage group at Cold Spring Harbor to concentrate their research on seven specific bacteriophages (T1 -- T7), so that they could readily compare results. T2, T4, and T6 are serologically related and have large genomes. T3 and T7 are also related to each other serologically. T1 and T5 are not related to any other bacteriophages.

Biochemistry, or biological chemistry -- The study of the chemical substances and vital processes occurring in living organisms; "the chemistry of life," or the study of the structure and properties of molecules in living organisms and how those molecules are made, changed, and broken down.

Cell-free system -- A mixture of cytoplasmic and/or nuclear components from cells used for in vitro protein synthesis, transcription, DNA replication, or other purposes.

Chromatin -- A deoxyribonucleic acid attached to a protein (primarily histone) structure base that makes up chromosomes in the nucleus of animal cells and is the carrier of genes in inheritance. It forms the more readily stainable portion of the cell nucleus, and coils and folds tightly during cell division.

Chromatography -- Any of a diverse group of techniques used to separate mixtures of substances according to their relative affinities for two different media, one a moving fluid or a gas (called the mobile phase), the other a porous solid or gel or a liquid applied to a solid support (the stationary phase of sorbent). Each substance is carried along the mobile phase at a different speed determined by its solubility (in a liquid mobile phase) or its vapor pressure (in a gas mobile phase) and on its affinity for the sorbent.

DNA, or deoxyribonucleic acid -- The fundamental substance of which genes are composed; an antiparallel double helix of nucleotides linked by phosphodiester, or sugar-phosphate, bonds to adjacent nucleotides in the same chain and by hydrogen bonds to complementary nucleotides in the opposite chain.

Electrophoresis -- The separation of electrically charged substances in solution based on differences in their rates of migration in an applied electric field.

Enzyme -- Enzymes are proteins found in living things that act to catalyze specific reactions. Made up of a complex of amino-acids, enzymes are part of every chemical reaction in living things. They aid in digestion, the growth and building of cells, and all reactions involving transformation of energy. Inside the cell, enzymes create RNA and DNA by facilitating the reaction of ribose with adenosine. They also specify the sites for linking to build RNA along a DNA template.

Genetic engineering -- The popular term for recombinant DNA technology.

Genome -- The complete gene complement, or full set of genes, of an organism, contained in a set of chromosomes in higher organisms (eukaryotes), a single chromosome in bacteria, and a DNA or RNA molecule in viruses. In a human being, the set of genes derived from one parent (the haploid set) contains about three billion base pairs and 50,000 to 100,000 genes.

Genetics -- The branch of biology that deals with heredity, especially the mechanisms of hereditary transmission of inherited characteristics among similar or related organisms.

Histone -- Any of a group of simple proteins, soluble in water and insoluble in dilute ammonia. Combined with nucleic acids they form nucleohistone, and are associated with DNA in chromatin.

In vitro -- An experimental situation outside a living cell or organism; biological or chemical work done in the test tube, instead of in living systems. "In vitro" is Latin for "in glass."

In vivo -- An experimental situation in a living cell or organism; biological or chemical work done in living systems.

Long interspersed nucleotide elements (LINEs) -- Mobile genetic elements that have dispersed and accumulated in the genomes of higher organisms via transposition, with up to 100,000 copies in mammalian genomes. In humans, LINEs are the major source of insertional mutagenesis.

Messenger RNA, or mRNA -- An RNA molecule transcribed from the DNA of a gene, and from which a protein is translated by the action of ribosomes. The basic function of the nucleotide sequence of mRNA is to determine the amino acid sequence in proteins.

Metabolism -- The chemical reactions occurring in a living cell which provide energy for vital processes and activities, and assimilate new material.

Molecular biology -- The branch of biology dealing with the formation, structure, and function of macromolecules essential to life, such as DNA, RNA, and proteins, especially their role in cell replication and the transmission of genetic information.

Mutation -- The process that produces a gene or a chromosome that differs from the wild-type. This process, either through an alteration in the nucleotide sequence of the DNA coding for a gene or through a change in the physical arrangement of a chromosome, results in the creation of a new character or trait not found in the parental type.

Nucleic acid -- A large molecule composed of nucleotide subunits.

Nucleotide -- A nucleic acid base, or nucleoside, linked with a ribose or deoxyribose sugar and a phosphate group, as occurs in ribonucleic and deoxyribonucleic acid.

Paper chromatography -- A type of chromatography in which the stationary phase is a sheet of special-grade filter paper.

Phenylalanine -- A nonpolar amino acid.

Phosphorylase -- An enzyme that catalyzes the production of glucose phosphate from glycogen and inorganic phosphate.

Polymer -- A molecule composed of repeated subunits, or individual polypeptide chains in a protein containing more than one polypeptide chain.

Polymerase -- An enzyme that catalyzes the synthesis of nucleic acids on preexisting nucleic acid templates, such as assembling RNA from ribonucleotides or DNA from deoxyribonucleotides.

Polynucleotide -- A DNA or RNA polymer composed of multiple nucleotides.

Polynucleotide phosphorylase -- An enzyme that catalyzes the breakdown of RNA in vivo, but that in the laboratory can be used to catalyze the synthesis of RNA polymers from individual nucleotides. To do so it does not require a template, and the sequence of the product RNA depends on the number and concentration of particular nucleotides (for example, uracil) present in the substrate. It is thus not an enzyme that plays a role in copying genetic material for expression.

Polypeptide -- A chain of linked amino acids. When folded in a particular three-dimensional configuration, it becomes a protein.

Polyribonucleotide -- An oligonucleotide, a short polymer of two to twenty nucleotides, consisting of a number of ribonucleotides, which are the nucleotides that contain ribose as their sugar, and which are components of RNA.

Polyuridylic acid, or Poly-U -- RNA or a segment of RNA that is composed of a polynucleotide chain consisting entirely of uracil, a pyrimidine, the parent compound of many drugs, including the barbiturates, base that appears in RNA in place of thymine found in DNA.

Protein -- A large molecule composed of one or more chains of amino acids in a specific order. The order is determined by the base sequence of nucleotides in the gene that codes for the protein. Proteins are required for the structure, function, and regulation of the body's cells, tissues, and organs. Each protein has unique functions.

Recombinant DNA, rDNA, hybrid strings -- A unique DNA sequence formed by the joining, usually in vitro, of two non-homologous DNA molecules.

Restriction enzyme -- An endonuclease which recognizes a specific sequence of bases in a DNA molecule. Each restriction enzyme has a single, specific recognition sequence, and binds to a DNA molecule at a specific site. As a result, treatment of a particular DNA molecule with a particular restriction enzyme will always produce the same set of DNA fragments.

Ribonucleotide -- A subunit that polymerizes into the nucleic acid RNA. Each nucleotide consists of a nitrogenous base, a sugar (ribose), and one to three phosphate groups.

RNA, or ribonucleic acid -- A single-stranded nucleic acid that performs an important role in the flow of genetic information. It is similar to DNA but has ribose sugar, rather than deoxyribose sugar, and uracil, rather than thymine, as one of the pyrimidine bases.

RNase, or ribonuclease -- Any nuclease specifically catalyzing the cleavage of phosphate ester linkages in ribonucleic acids. Ribonucleases are grouped as those cleaving internal bonds, the endoribonucleases, and those cleaving at termini, the exoribonucleases.

Simian virus 40 (SV 40) -- A polyomavirus isolated from Rhesus monkey kidney tissue, which transforms human and newborn hamster kidney cell cultures into cancer cells, and on inoculation into newborn hamsters produces tumors. It does not produce cancer in humans or other primates.

Transposition -- The movement of a DNA segment within the genome of an organism.

Uracil -- A pyrimidine (the parent compound of many drugs, including the barbiturates) base that is an essential constituent of RNA, but not DNA.

Virus -- Any one of a group of minute infectious agents that are not visible under a light microscope and are characterized by a lack of independent metabolism and an ability to replicate only within living host cells. Even though they are not living organisms, like living organisms they have the ability to pass genes through multiple generations and to mutate. The individual virus particle consists of a strand or strands of nucleic acid (which may be either DNA or RNA) and a protein shell. Viruses are classified into three main subgroups based on their host, bacterial viruses, plant viruses, and animal viruses. Viruses are then further classified by their origin, means of transmission, or illnesses they produce.