Boldface terms within a definition are also defined in this glossary.

Figures and tables that illustrate defined terms are noted in parentheses.

lagging strand One of the two daughter DNA strands formed at a replication fork as short, discontinuous segments (Okazaki fragments), which are synthesized in the 5' → 3' direction and later joined. See also leading strand. (Figure 5-29)

laminin Large heterotrimeric multi-adhesive matrix protein that is found in all basal lamina. (Figure 20-23)

lamins A group of intermediate filament proteins that form a fibrous network, the nuclear lamina, on the inner surface of the nuclear envelope.

late endosome See endosome.

lateral See basolateral.

lateral inhibition Important signal-mediated developmental process that results in adjacent equivalent or near-equivalent cells assuming different fates.

leading strand One of the two daughter DNA strands formed at a replication fork by continuous synthesis in the 5' → 3' direction. The direction of leading-strand synthesis is the same as movement of the replication fork. See also lagging strand. (Figure 5-29)

lectin Any protein that binds tightly to specific sugars. Lectins assist in the proper folding of some glycoproteins in the endoplasmic reticulum and can be used in affinity chromatography to purify glycoproteins or as reagents to detect them in situ.

leucine zipper A type of coiled-coil structural motif composed of two α helices that form specific homo- or heterodimers; common motif in many eukaryotic transcription factors. See coiled coil. (Figures 9-30c and 3-10)

ligand Any molecule, other than an enzyme substrate, that binds tightly and specifically to a macromolecule, usually a protein, forming a macromolecule-ligand complex.

linkage In genetics, the tendency of two different loci on the same chromosome to be inherited together. The closer two loci are, the lower the frequency of recombination between them and the greater their linkage.

G-15

lipid Any organic molecule that is poorly soluble or virtually insoluble in water but is soluble in nonpolar organic solvents. Major classes include fatty acids, phospholipids, steroids, and triglycerides.

lipid-anchored membrane protein Any protein that is tethered to a cellular membrane by one or more covalently attached lipid groups, which are embedded in the phospholipids bilayer. (Figure 10-19)

lipid raft Microdomain in the plasma membrane that is enriched in cholesterol, sphingomyelin, and certain proteins.

lipoprotein Any large, water-soluble protein and lipid complex that functions in mass transfer of lipids throughout the body. See also low-density lipoprotein (LDL).

liposome Artificial spherical phospholipid bilayer structure with an aqueous interior that forms in vitro from phospholipids and may contain membrane proteins. (Figure 7-3c)

long interspersed elements (LINEs) Abundant mobile elements in mammals generated by retrotransposons lacking long-terminal repeats. (Figure 8-17)

long noncoding RNA (lncRNAs) RNA molecules of many kb in length that do not encode open reading frames. Some lncRNAs function in repression of gene transcription by forming a scaffold to which several proteins bind, forming an RNA-protein complex that affects chromatin structure.

long terminal repeats (LTRs) Direct repeat sequences, containing up to 600 base pairs, that flank the coding region of integrated retroviral DNA and viral retrotransposons.

low-density lipoprotein (LDL) A class of lipoprotein, containing apolipoprotein B-100, that is a primary transporter of cholesterol in the form of cholesteryl esters between tissues, especially to the liver. (Figure 14-27)

lumen The aqueous interior of an organelle.

lymphocytes Two classes of white blood cells that can recognize foreign molecules (antigens) and mediate immune responses. B lymphocytes (B cells) are responsible for production of antibodies; T lymphocytes (T cells) are responsible for destroying virus and bacteria-infected cells, foreign cells, and cancer cells.

lysis Destruction of a cell by rupture of the plasma membrane and release of the contents.

lysogeny Phenomenon in which the DNA of a bacterial virus (bacteriophage) is incorporated into the host-cell genome and replicated along with the bacterial DNA but is not expressed. Subsequent activation leads to formation of new viral particles, eventually causing lysis of the cell.

lysosome Small organelle that has an internal pH of 4–5, contains hydrolytic enzymes, and functions in degradation of materials internalized by endocytosis and of cellular components in autophagy. (Figures 1-12 and 4-13)