- The smallest unit of a substance that can exist alone and retain the character of that substance.
* * *The smallest possible quantity of a di-, tri-, or polyatomic substance that retains the chemical properties of the substance. [Mod. L. molecula, dim. of L. moles, mass]- accessory molecules cell surface adhesion molecules on T cells that are involved in binding of one cell to another cell activation, and in signal transduction, e.g., CD4.- adhesion molecules molecules that are involved in T helper-accessory cell, T helper-B cell, and T cytotoxic-target cell interactions; extracellular matrix proteins that attract leukocytes from the circulation.- cell adhesion m. (CAM) proteins that hold cells together, e.g., uvomorulin, and hold them to their substrates, e.g., laminin.- chimeric m. a m. (usually a biopolymer) containing sequences derived from two different genes; specifically, from two different species. Cf.:chimera.- class I m. a major histocompatibility complex antigen made up of two noncovalently bonded polypeptide chains, one glycosylated, heavy, and variable with antigen specificity; the other chain is β2-microglobulin.- class II m. a major histocompatibility complex membrane-piercing antigen made up of two noncovalently bonded polypeptide chains designated α and β.- costimulatory m. membrane-bound or secreted product of accessory cells that is required for signal transduction.- endothelial-leukocyte adhesion m. (E-LAM) a glycoprotein on the surface of endothelial cells that is involved in blood leukocyte attachment to vessel walls as well as emigration from the vessels into the tissues.- gram-m. the amount of a substance with a mass in grams equal to its molecular weight; e.g., a gram-m. of hydrogen weighs 2.016 g, that of water 18.015 g.- intercellular adhesion m.-1 (ICAM-1) a glycoprotein that is expressed on a variety of cells. It is the ligand for LFA-1 as well as the receptor for the rhinoviruses.- lectin pathway m. the binding of mannose-binding protein to bacterial carbohydrates resulting in activation of the complement pathway.
* * *mol·e·cule 'mäl-i-.kyü(ə)l n the smallest particle of a substance that retains all the properties of the substance and is composed of one or more atoms
* * *mol·e·cule (molґə-kūl) [L. molecula little mass] a very small mass of matter; the smallest amount of a substance which can exist alone; an aggregation of atoms; specifically, a chemical combination of two or more atoms which form a specific chemical substance. To break up the molecule into its constituent atoms is to change its character. The number and kind of atoms in a molecule vary with the compound. molecular adj
Medical dictionary. 2011.