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(BQ) Part 2 book “Harper’s illustrated biochemistry” has contents: Biochemical case histories, the biochemistry of aging, white blood cells, red blood cells, plasma proteins & immunoglobulins, muscle & the cytoskeleton, the extracellular matrix, clinical biochemistry, hormone action & signal transduction, and other contents. | SECTION VIII Biochemistry of Extracellular & Intracellular Communication CHAPTER 40 Membranes: Structure & Function P. Anthony Weil, PhD OBJECTIVES After studying this chapter, you should be able to: Know that biologic membranes are mainly composed of a lipid bilayer and associated proteins and glycoproteins. The major lipids are phospholipids, cholesterol, and glycosphingolipids. Appreciate that membranes are asymmetric, dynamic structures containing a mixture of integral and peripheral proteins. Describe the widely accepted fluid mosaic model of membrane 1120 structure. Understand the concepts of passive diffusion, facilitated diffusion, active transport, endocytosis, and exocytosis. Recognize that transporters, ion channels, the Na+ − K+-ATPase, receptors, and gap junctions are important participants in membrane function. Be aware that a variety of disorders result from abnormalities of membrane structure and function, including familial hypercholesterolemia, cystic fibrosis, hereditary spherocytosis, among others. BIOMEDICAL IMPORTANCE Membranes are dynamic, highly fluid structures consisting of a lipid bilayer and associated proteins. Plasma membranes form closed compartments around the cytoplasm to define cell boundaries. The plasma membrane has selective permeabilities and acts as a barrier, thereby maintaining differences in composition between the inside and outside of the cell. Selective membrane molecular permeability is generated through the action of specific transporters and ion channels. The plasma membrane also exchanges material with the extracellular environment by exocytosis and endocytosis, and there are special areas of membrane structure—gap junctions—through which adjacent cells may communicate by exchanging material. In addition, the plasma membrane plays key roles in cell–cell interactions and in transmembrane signaling. Membranes also form specialized compartments within the cell. Such intracellular membranes help shape many of the
