Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Membranes surround and compartmentalize cells Cytoplasm Figure 5.10 Extracellular space
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phospholipids are the main structural components of membranes Each has a hydrophilic head and two hydrophobic tails Membrane phospholipids form a bilayer CH 2 CH 3 CH 2 CH CH 2 CH 3 CH 2 CH 3 N + O O O–O– P O CH 2 CH CH 2 C O C O O O Phosphate group Symbol Hydrophilic head Hydrophobic tails
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In water, phospholipids form a stable bilayer Figure 5.11B Hydrophilic heads Hydrophobic tails Water –The heads face outward and the tails face inward Hydrophilic heads
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The membrane is a fluid mosaic of phospholipids and proteins
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Proteins make the membrane a mosaic of function Figure 5.13
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Proteins make the membrane a mosaic of function
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Only small or nonpolar molecules can diffuse freely through a membrane Diffusion of polar molecules requires facilitation by a transport protein. Diffusion is facilitated.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Substances will diffuse through artificial membranes. No additional energy required. Molecules flow down their concentration gradient. But what if the membrane is selectively permeable? Passive transport is diffusion
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In osmosis, water travels from an area of lower solute concentration to an area of higher solute concentration Osmosis is the passive transport of water edu/people/gianni ni/flashanimat/tran sport/osmosis.swf
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Water balance between cells and their surroundings is crucial to organisms
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings ( fresh water) (seawater) Dilute urine produced by kidney; Active uptake of salt by gills to replace salts. Concentrated urine produced by kidney; Fish drinks seawater and actively eliminates salt by gills. Passive entry of water Passive exit of water Passive exit of salt Active elimination of salt Active elimination of water Active uptake of salt Passive entry of salt Active uptake of water + salt (OSMOTIC REGULATION)
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Active transport against a concentration gradient
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Sodium-Potassium Pump
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Exocytosis transport large molecules out of a cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Endocytosis transports large molecules into a cell
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Familial hypercholesterolemia
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings active transport concentration gradient energy (ATP) facilitated transport Small or nonpolar molecules