P三 CELL PHYSIOLOGY I Plasma membrane A. The structure of the plasma membrane allows the separatio reation of listinct molecular environments within cells. The lipid bilay lar to thin layers of oil surrounding fluid ozone. Thus, the lipid bilayer cell into functional compartments B. The fluid mosaic model is the accepted view of the molecular nature of plasma 1. The model proposes that proteins traverse the lipid bilayer and are incorpo rated within the lipid 2. Proteins and lipids can move freely in the plane of the membrane, producing C. The plasma membrane is composed of phospholipids and proteins. 1. Membrane lipids can be classified into three major classes: phospholipids, a. Phospholipids are the most abundant membrane lipids (1)They have a bipolar(amphipathic) nature, containing a charged head d two hydrophobic(water-insoluble, noncharged )tails. (2)The hydrophobic tails face each other, forming a bilayer and exposing the polar head group to the aqueous environment on either side of th membrane allows them to insert into membranes. These lipids can be modified by the addition of carbohydrate units at their polar end, creating glycosphingo- lipids in brain cells. c. Cholesterol is the predominant sterol (unsaturated alcohols found in animal and plant tissues) in human cells; it increases the fluidity of the membrane by rting itself between phospholipids, improving membrane stabilit TAY-SACHS DISEASE The accumulation of glycosphingolipid associated with Tay-Sachs disease causes paralysis and impair- 2. Membrane proteins that span the lipid bilayer are known as integral mem- brane proteins, whereas those associated with either the inner or the outer Copyright o 2003 by The McGraw-Hill Companies, Inc. Click here for Terms of UsN CHAPTER 1 CHAPTER 1 CELL PHYSIOLOGY 1 I. Plasma Membrane A. The structure of the plasma membrane allows the separation and creation of distinct molecular environments within cells. The lipid bilayer is similar to thin layers of oil surrounding fluid ozone. Thus, the lipid bilayer divides the cell into functional compartments. B. The fluid mosaic model is the accepted view of the molecular nature of plasma membranes. 1. The model proposes that proteins traverse the lipid bilayer and are incorpo￾rated within the lipids. 2. Proteins and lipids can move freely in the plane of the membrane, producing the fluid nature of the membrane. C. The plasma membrane is composed of phospholipids and proteins. 1. Membrane lipids can be classified into three major classes: phospholipids, sphingolipids, and cholesterol. a. Phospholipids are the most abundant membrane lipids. (1) They have a bipolar (amphipathic) nature, containing a charged head group and two hydrophobic (water-insoluble, noncharged) tails. (2) The hydrophobic tails face each other, forming a bilayer and exposing the polar head group to the aqueous environment on either side of the membrane. b. Sphingolipids have an amphipathic structure similar to phospholipids that allows them to insert into membranes. These lipids can be modified by the addition of carbohydrate units at their polar end, creating glycosphingo￾lipids in brain cells. c. Cholesterol is the predominant sterol (unsaturated alcohols found in animal and plant tissues) in human cells; it increases the fluidity of the membrane by inserting itself between phospholipids, improving membrane stability. TAY-SACHS DISEASE The accumulation of glycosphingolipid associated with Tay-Sachs disease causes paralysis and impair￾ment of mental function. 2. Membrane proteins that span the lipid bilayer are known as integral mem￾brane proteins, whereas those associated with either the inner or the outer CLINICAL CORRELATION 5506ch01.qxd_ccII 2/17/03 2:08 PM Page 1 Copyright © 2003 by The McGraw-Hill Companies, Inc. Click here for Terms of Use