Terms Starting with Letter: E echocardiogram An ultrasound record of the motion, size, and composition of various cardiac structures. This technique utilizes sound waves at high frequencies in order to generate images of the heart. ectopic away from normal position electrophoresis A technique for separating macromolecules from one another in a mixture based on their molecular weight and electrical charge. The mixture is placed in a gel or other medium and subjected to an electrical current. embolus Any foreign matter, as a blood clot or air bubble, brought by the blood through a larger vessel and forced into a smaller one obstructing circulation. endocytosis Uptake of extracellular materials (solid or liquid) into the cell by invagination of the plasma membrane forming a small membrane-bound vesicle. Contrast agents can be trapped by enhanced endocytosis in tumor cells. endosome Membrane-bound vesicle within the cytoplasm of the cell formed from endocytosis. engineered transferrin receptor (ETR) MR imaging marker receptor that has been genetically modified to promote the internalization of monocrystalline iron oxide nanoparticlese changing the relaxivity of the targeted cell. enzyme A biological macromolecule, on the surface of which are chemical groups so arranged to act as a catalyst by lowering the activation energy of a reaction. Enzymes are proteins or RNAs. See Ribozyme. epitope The part of an antigen that binds to the antigen-binding region of an antibody. Also called antigenic determinant. ex vivo Latin meaning "out of or from life." Refers to tissues or cells that have been removed from animals after death for analysis. exocytosis A process by which intercellular vesicles fuse with the plasma membrane and empty their contents to the outside. expression See gene expression. expression analysis Study of cellular gene expression. expression vector Plasmid that has been genetically engineered to be used for the expression of transgenes.