PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson | Chapter 7 Membrane Structure and Function Overview: Life at the Edge The plasma membrane is the boundary that separates the living cell from its surroundings The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 7-1 Figure How do cell membrane proteins help regulate chemical traffic? Concept : Cellular membranes are fluid mosaics of lipids and proteins Phospholipids are the most abundant lipid in the plasma membrane Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings For the Cell Biology Video Structure of the Cell Membrane, go to Animation and Video Files. Membrane Models: Scientific Inquiry Membranes | Chapter 7 Membrane Structure and Function Overview: Life at the Edge The plasma membrane is the boundary that separates the living cell from its surroundings The plasma membrane exhibits selective permeability, allowing some substances to cross it more easily than others Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 7-1 Figure How do cell membrane proteins help regulate chemical traffic? Concept : Cellular membranes are fluid mosaics of lipids and proteins Phospholipids are the most abundant lipid in the plasma membrane Phospholipids are amphipathic molecules, containing hydrophobic and hydrophilic regions The fluid mosaic model states that a membrane is a fluid structure with a “mosaic” of various proteins embedded in it Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings For the Cell Biology Video Structure of the Cell Membrane, go to Animation and Video Files. Membrane Models: Scientific Inquiry Membranes have been chemically analyzed and found to be made of proteins and lipids Scientists studying the plasma membrane reasoned that it must be a phospholipid bilayer Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 7-2 Hydrophilic head WATER Hydrophobic tail WATER Figure Phospholipid bilayer (cross section) In 1935, Hugh Davson and James Danielli proposed a sandwich model in which the phospholipid bilayer lies between two layers of globular proteins Later studies found problems with this model, particularly the placement of membrane proteins, which have hydrophilic and hydrophobic regions In 1972, J. Singer and G. Nicolson proposed that the membrane is a mosaic of proteins dispersed within the bilayer, with only the hydrophilic regions exposed to water Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 7-3 Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein Figure The fluid .
