Alpha-helix -- A short, helical arrangement of a polypeptide chain that is a common secondary structure in proteins. In the alpha-helix, the polypeptide folds by twisting into a right handed screw so that all the amino acids can form hydrogen bonds with each other.

Amino acid -- The basic building block of proteins and polypeptides; containing a basic amino group, an acidic carboxyl group, and a side chain attached to an alpha carbon atom, and that link together by peptide bonds to form proteins or that 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.

Antigen -- A molecule whose shape triggers the production of antibodies, or immunoglobulins, that will bind to the antigen. It can also be a foreign substance capable of triggering an immune response in an organism.

Applied chemistry -- The application of the theories and principles of chemistry to practical purposes.

Biomolecule -- Any organic molecule that is an essential part of a living organism.

Chemical bonds -- Attachments of atoms formed by sharing or exchanging electrons.

Chemical engineering -- The branch of engineering that deals with the technology of large-scale chemical production and the manufacture of products through chemical processes.

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.

Denaturation -- In chemistry, it is the process of causing the tertiary structure of a protein to unfold, either with heat, an alkali, or acid, so that some of its original properties are diminished or eliminated.

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.

Genetic disease -- A disease that has its origin in changes to DNA; usually refers to diseases that are inherited, although non-inherited forms of cancer can result from DNA mutation.

Germ plasm -- The cytoplasm of a germ cell, especially the part containing chromosomes; or hereditary material or genes. Also called plasm.

Hemoglobin -- The iron-rich respiratory pigment in red blood cells of vertebrates, consisting of about 6 percent heme (the prosthetic groups of cytochromes) and 94 percent polypeptide globin.

Hydrogen bond -- A weak bond by which an atom in an inorganic molecule shares an electron with a hydrogen atom.

Immunology -- The branch of biomedicine concerned with the structure and function of the immune system, the bodily distinction of self from nonself, and laboratory techniques involving the interaction of antigens with specific antibodies.

Inorganic molecule -- A molecule that lacks carbon, such as nitrate (NO3) or ammonium (NH4).

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

Niacin -- A white crystalline acid that is a component of the vitamin B complex found in meat, wheat germ, dairy products, and yeast and is used to treat and prevent pellagra, a disease caused by malnutrition (specifically a deficiency of niacin) that is characterized by skin eruptions, digestive and nervous system disturbances, and eventual mental deterioration.

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.

Organic chemistry -- The chemistry of carbon compounds.

Organic molecule -- A molecule that contains carbon, such as butane (C4H10) or ethanol (C2H6O).

Orthomolecular medicine -- The concept termed by Pauling that optimal health could result from ensuring that the right molecules were present in the right amount in the body; it is also strongly associated with vitamin megadosing.

Peptide -- Any of various natural or synthetic compounds containing two or more amino acids linked by the carboxyl group of one amino acid to the amino group of another.

Phenylketonuria, or PKU -- An inherited human metabolic disease caused by a mutation in a gene coding for a phenylalanine processing enzyme--phenylalanine hydroxylase--which leads to accumulation of phenylalanine and mental retardation if not treated.

Polypeptide -- A chain of linked amino acids, or a protein.

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.

Quantum mechanics, or wave mechanics -- A theory of matter that is based on the concept of the possession of wave properties by elementary particles and affords a mathematical interpretation of the structure and interactions of matter on the basis of these properties and that incorporates within it quantum theory and the uncertainty principle.

Schizophrenia -- A psychotic disorder characterized by loss of contact with the environment, by noticeable deterioration in the level of functioning in everyday life, and by disintegration of personality expressed as disorder of feeling, thought (as in hallucinations and delusions), and conduct.

Sickle-cell anemia -- A chronic anemia that occurs primarily in individuals of African descent who are homozygous (a gene pair that possesses identical alleles) for the gene controlling hemoglobin S. The condition is characterized by destruction of red blood cells and by episodic blocking of blood vessels by the adherence of sickle cells to the lining of the vessels and heart which can cause serious complications, such as organ failure.

Structural chemistry -- The branch of chemistry that focuses on the study of the formation of compounds and chemical bonds.

Vitamin C, or ascorbic acid -- A white, crystalline vitamin found in citrus fruits, tomatoes, potatoes, and leafy green vegetables and used to prevent scurvy.

X-ray crystallography -- The study of crystal structure by means of x-ray diffraction.