Lamins: A family of intermediate filaments that form the nuclear skeleton. They are associated with nuclear pores, and their phosphorylation is a key regulatory event during mitosis. Phosphorylation triggers nuclear dissolution; dephosphorylation is associated with nuclear reorganization.

Large Ribosomal Subunit: 60S (in prokaryotes) or 70S (in eukaryotes) ribosomal subunit.

Lectins: A group of compounds, many of which are isolated from plants, that can bind tightly to carbohydrate groups of proteins. Some, like ricin, are highly toxic. Others, however, are useful because they can be used either in situ or in affinity chromatography to purify proteins by binding to their carbohydrate groups.

Leukemia: A classification of diseases often characterized by the overproduction of leukocytes, or white blood cells.

Leukocytes (White Blood Cells):

A nucleated blood cell family that includes macrophages, neutrophils, and lymphocytes, all important in fighting disease in the immune response.

Ligand: Any molecule that binds tightly to another macromolecule, as when a hormone (the ligand) binds to its receptor. A ligand-receptor complex often triggers a cell-signaling event.

Liposomes: Pure, synthetic phospholipid bilayers useful for delivering hydrophilic molecules to the interior of cells through liposome-cell fusion.

Lysosomes: Acidic, single-membrane organelles that contain enzymes designed to hydrolyze nearly all biological molecules. Lysosomal enzymes operate optimally at an acidic pH.

Lytic: Describing the process in which viruses invade a host cell and cause the lysis of the cell through the production of new virus particles.