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CHAPTER 2 THE CELL: BASIC UNIT OF STRUCTURE AND FUNCTION I. The Study of Cells II. A Prototypical Cell III. Plasma Membrane A. Basic description i. Aka plasmalemma ii. Selective permeability/semipermeability iii. Surface area must be large enough to transport everything needed, but as cell grows, surface area increases by square units while volume increases by cubic units, (so most cells stay small) B. Composition and Structure of Membranes i. Fluid matrix of about an equal amt of lipids and proteins (by mass). The lipids form the main structure but the proteins determine its primary functions. There is also an external glycocalyx layer (carbohydrate coat) ii. Lipids (3 in plasma membrane) 1. Phosphilipids (most of the membrane) A. Both polar (head) and nonpolar (tail) parts, and phosphate. B. Makes up the phospholipids bilayer , which keeps the ICF in and the ECF out. i. Interstitial fluid is an ECF. It bathes the external cell surface. 2. Cholesterol (~20%) A. A type of steroid B. Scattered within the hydrophobic tails to strengthen it an stabilize it at extreme temperatures. 3. Glycolipids (~5-10%) A. Lipids with attached carb group B. Only on the outer membrane, exposed to ECF C. Glycocalys —the carb portion of the glycolipid. Helps glycolipids do cell recognition, intracellular adhesion, and communication. iii. Proteins (2) 1. Most of the membrane’s specific functions are determined by proteins 2. Integral protein —embedded within and extend across the bilayer. A. Some are membrane channels (protein has hole where things pass) B. Others are receptors—binding sites for outside molecues. C. Many are glycoproteins (proteins w attached carb groups). This forms ~90% of all the membrane molecules that have carb chains attached. 3. Peripheral protein —loosely attached (not embedded) on the internal or external surface, often to the exposed parts of the integral proteins. They can “float” around the membrane. 4. integral and peripheral proteins can both be enzymes iv. glycocalys —fuzzy stuff on the outside of the membrane made up of the carb groups attached to glycoproteins and glycolipids.
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C. Protein-Specific Functions of the Plasma Membrane (6) i. Transport —transmembrane proteins span the entire membrane. (internal hydrophobic, external hydrophilic). The protein assists the transport of a substance across the membrane, and this sometimes requires ATP (E is released when the last bond that attaches phosphate to the rest of the molecule is broken) ii. Intercellular connection —junctions b/w cells can form when proteins on membranes attach. iii. Anchorage for the cytoskeleton —cell shape maintained when structural proteins in the cell (cytoskeleton) attach to membrane proteins. iv.
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This note was uploaded on 03/30/2010 for the course BIO 1004 taught by Professor Nef during the Spring '10 term at Holy Family University.

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