Terms Starting with Letter: L label A fluorescent chemical group or radioactive isotope added to a molecule in order to permit identification of the molecule at a later time. laser capture microscopy (LCM) The microdissection of a tissue sample to extract a sample of cells for either DNA or mRNA analysis using laser-warmed plastic film. lateral Away from the midline of the body; on the outer side of. leucine An essential amino acid. ligand Any molecule, other than an enzyme substrate, that binds tightly and specifically to a receptor site of another molecule. linkage Association between two or more markers (e.g., genes) on the same chromosome such that they will generally be inherited together. The closer they are, the lower the frequency of recombination. linkage map A map showing the relative positions of genetic loci on a given chromosome based on the frequency of the inheritance of the loci. liposome Phospholipid bilayer containing an aqueous interior that forms in vitro from phospholipids and may contain proteins. May be synthetically engineered to contain specific drugs, genes or contrast agents to transport into cells. locus The position of a gene on a chromosome. luciferase Luciferase is the key enzyme for bioluminescence and is produced, amongst others, by the following organisms: fireflies, glowworms, fungi and jellyfish. lymph The fluid contained in the lymphatic vessels. The lymphatic system consists of the lymph, lymph vessels, lymph nodes, thymus, and spleen. The primary function of the lymphatic system is to drain fluid that escapes from the blood capillaries. The lymph also contains leukocytes (white blood cells). These cells are involved in cellular immunity and the formation of antibodies. lysosome Small, membrane bound, cytoplasmic organelle having hydrolytic enzymes which aids in the digestion of other macromolecules found in the rest of a cell..