Amino acid -- The basic building block of proteins and polypeptides. It contains a basic amino group, an acidic carboxyl group, and a side chain attached to an alpha carbon atom. Amino acids link together by peptide bonds to form proteins, or function as chemical messengers and as intermediates in metabolism.

Antibody -- Any of the protein molecules produced by specialized immune system cells (B cells) that can recognize and bind to a particular foreign antigen. If the antigen is on the surface of a cell, this binding leads to cell aggregation and subsequent destruction. Antibodies are also referred to as immunoglobulins.

ATP, or Adenosine triphosphate -- Nucleoside triphosphate composed of adenine, ribose, and three phosphate groups that is the primary carrier of chemical energy in cells. The terminal phosphate groups are highly reactive in the sense that their hydrolysis, or transfer to another molecule, takes place with the release of a large amount of free energy.

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.

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.

Chromatography -- Any of several techniques for the separation or purification of complex mixtures that rely on the differential affinities, or the attractions or forces between particles that cause them to combine, of substances for a gas or liquid mobile medium (such as gelatin) and for a stationary adsorbing medium (such as paper) through which they pass.

Chymotrypsin -- An enzyme that catalyses the hydrolysis (the breakdown) of proteins into peptides or amino acids in the small intestine. It is selective for peptide bonds with aromatic or large hydrophobic side chains on the carboxyl side of this bond. Chymotrypsin also catalyses the hydrolysis of ester bonds.

DNA, or deoxyribonucleic acid -- The primary genetic material of all cellular organisms and the DNA viruses. Located predominantly in cell nuclei, it is composed of two chains of nucleotides -- deoxyribose and phosphate backbones with side chains of purine (adenine or guanine) or pyrimidine (cytosine and thymine) bases projecting inward. Hydrogen bonds link adenine to guanine, and cytosine to thymine. The two linked strands are twisted in a double helix.

Electrophoresis -- See "gel electrophoresis"

Enzyme -- A protein molecule that catalyzes chemical reactions of other substances without itself being destroyed or altered by the 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. Each enzyme works only on one specific substance (called the substrate). Enzymes are usually designated by the suffix -ase.

Factor-In cell physiology and biochemistry -- Any of several substances that are necessary to produce a result, e.g., a growth factor. Often, use of the term "factor" indicates that the chemical nature of the substance or its mechanism of action is unknown, as in endocrinology, where "factors" are renamed as "hormones" when their chemical nature is determined.

Gel electrophoresis -- The separation of the molecules of various ionic compounds dissolved in solution based on the compounds' different rates of movement through an electric field applied to the solution. Gel electrophoresis uses a gel in the form of tubes or a thin slab as a non-reacting support medium, which holds the molecules of the ionic compounds as they move in the conducting medium, in order to prevent diffusion of the compounds.

Immunoglobulin -- See "antibody"

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."

Mapping, gene -- Determination of the relative positions of genes on a chromosome (or other DNA molecule) and of the distance, in linkage units or physical units, between them.

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.

Myeloma -- A primary tumor of the bone marrow. Multiple myeloma is a disseminated plasma cell cancer affecting multiple sites in the bone marrow and causing a reduction in the immune antibodies produced by the plasma cells.

Neoplasm -- A new growth of tissue serving no physiological function; a tumor.

Nucleotide -- A unit that polymerizes into nucleic acids (DNA or RNA). Each nucleotide consists of a purine (adenine or guanine) or pyrimidine (cytosine, thymine, or uracil) base, a sugar (ribose in the case of RNA, deoxyribose in the case of DNA), and a phosphate molecule.

Phage -- See "bacteriophage"

Plasma cell -- A mature "B" lymphocyte that secretes antibodies.

Polypeptide -- A chain of linked amino acids; 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.

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.

Protein synthesis -- The process in which the genetic code carried by messenger RNA directs cellular organelles called ribosomes to produce proteins from amino acids.

Recombinant DNA, rDNA, hybrid strings -- Genetically engineered DNA prepared in vitro by cutting up DNA molecules and splicing together specific DNA fragments, usually from more than one type of organism, e.g., inserting pieces of virus DNA into a bacterial plasmid.

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.

Ribosome -- A complex organelle composed of proteins and rRNA that catalyzes translation of messenger RNA into an amino acid sequence. Ribosomes consist of two non-identical subunits each consisting of a different rRNA and a different set of proteins.

RNA, or ribonucleic acid -- A single-stranded nucleic acid found in the cell nucleus and cytoplasm, which plays a key role in protein synthesis. (It also constitutes the genetic material of the RNA viruses.) It is similar to DNA but has ribose sugar, rather than deoxyribose sugar, and uracil, rather than thymine, as one of the pyrimidine bases. There are several classes of RNA molecules, including messenger RNA, transfer RNA, and ribosomal RNA, each serving a different purpose in the cell.

Sequencing, gene -- Determination of the order of nucleotides in a DNA or RNA molecule (sequencing can also determine the order of amino acids in a protein.)

Transfer RNA, or tRNA -- Small RNA molecules that carry amino acids to the ribosome for polymerization into a polypeptide. During translation, the amino acid is inserted into the growing polypeptide chain when the anticodon of the tRNA pairs with a codon on the mRNA (messenger RNA) being translated.

Trypsin -- A protein digesting enzyme made by the pancreas and active in the small intestine.

Virus -- Any one of a group of sub-microscopic infectious agents characterized by a lack of independent metabolism and by the ability to replicate only within living host cells. Whether regarded as extremely simple microorganisms or extremely complex molecules, 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.