Molecular Imprinting: A methodology for chemically synthesizing polymer molds of specific molecules or recognition sites of specific molecules. Applications for molecularly imprinted polymers (MIPs) include separations, assays and biosensors, and catalysis.alpha-Endorphin: An endogenous opioid peptide derived from BETA-LIPOTROPIN of the pro-opiomelanocortin (POMC) system. It is the 16-amino acid sequence of the N-terminal of BETA-ENDORPHIN and differs from GAMMA-ENDORPHIN by one amino acid (beta-endorphin 1-17).Genomic Imprinting: The variable phenotypic expression of a GENE depending on whether it is of paternal or maternal origin, which is a function of the DNA METHYLATION pattern. Imprinted regions are observed to be more methylated and less transcriptionally active. (Segen, Dictionary of Modern Medicine, 1992)Polymers: Compounds formed by the joining of smaller, usually repeating, units linked by covalent bonds. These compounds often form large macromolecules (e.g., BIOPOLYMERS; PLASTICS).