1. MEMBRANE STRUCTURE AND FUNCTION OVERVIEW
CHAPTER 8
MEMBRANE STRUCTURE AND FUNCTION OVERVIEW

2. Figure 8.2 Two generations of membrane models
I. MEMBRANE STRUCTURE
A. MEMBRANE MODELS HAVE EVOLVED TO FIT NEW DATA: SCIENCE AS A PROCESS
CURRENT MEMBRANE MODEL: FLUID MOSAIC MODEL
Figure 8.2 Two generations of membrane models

3. B. A MEMBRANE IS A FLUID MOSAIC OF LIPIDS, PROTEINS, AND CARBOHYDRATES
INTEGRAL PROTEINS ARE EMBEDDED IN THE LIPID BILAYER
PERIPHERAL PROTEINS ARE ATTACHED TO THE SURFACE
THE INSIDE AND OUTSIDE MEMBRANE FACES DIFFER IN COMPOSITION
CARBOHYDRATES LINKED TO PROTEINS AND LIPIDS IN THE PLASMA MEMBRANE ARE IMPORTANT FOR CEL-CELL RECOGNITION

4. Figure 8.5 The detailed structure of an animal cell’s plasma membrane

5. II. TRAFFIC ACROSS MEMBRANES
A. A MEMBRANE’S MOLECULAR ORGANIZATION RESULTS IN SELECTIVE PERMEABILITY
A CELL MUST EXCHANGE SMALL MOLECULES AND IONS WITH ITS SURROUNDINGS, A PROCESS CONTROLLED BY THE PLASMA MEMBRANE
HYDROPHOBIC SUBSTANCES ARE SOLUBLE IN LIPID AND PASS THROUGH MEMBRANES RAPIDLY
SMALL POLAR MOLECULES SUCH AS H2O ALSO PASS THROUGH THE MEMBRANE
LARGER POLAR MOLECULES AND IONS REQUIRE SPECIFIC TRANSPORT PROTEINS TO HELP THEM ACROSS

6. B. PASSIVE TRANSPORT IS DIFFUSION ACROSS A MEMBRANE
DIFFUSION: THE SPONTANEOUS MOVEMENT OF A SUBSTANCE DOWN ITS CONCENTRATION GRADIENT
Figure 8.9 Diffusion

7. C. OSMOSIS IS THE PASSIVE TRANSPORT OF WATER
WATER FLOWS ACROSS A MEMBRANE FROM THE SIDE WHERE SOLUTE IS LESS CONCENTRATED (HYPOTONIC) TO THE SIDE WHERE SOLUTE IS MORE CONCENTRATED (HYPERTONIC)
IF THE CONCENTRATIONS ARE EQUAL (ISOTONIC), NO NET OSMOSIS OCCURS

8. Figure 8.10 Osmosis

9. D. CELL SURVIVAL DEPENDS ON BALANCING WATER UPTAKE AND LOSS
CELLS LACKING CELL WALLS (AS IN ANIMALS) ARE ISOTONIC WITH THEIR ENVIRONMENTS OR HAVE ADAPTATIONS FOR OSMOREULATION
8.11 Water Balance of Living Cells

10. 8.13 Facilitated Diffusion
E. SPECIFIC PROTEINS FACILITATE THE PASSIVE TRANSPORT OF SELECTED SOLUTES
IN FACILITATED DIFFUSION, A TRANSPORT PROTEIN SPEEDS MOVEMENT OF A SOLUTE ACROSS A MEMBRANE DOWN ITS CONCENTRATION GRADIENT
8.13 Facilitated Diffusion

11. E. ACTIVE TRANSPORT IS THE PUMPING OF SOLUTES AGAINST THEIR GRADIENTS
SPECIFIC MEMBRANE PROTEINS USE ENERGY, USUALLY IN THE FORM OF ATP, TO DO THIS WORK
8.15 Passive and Active Transport Compared

12. G. SOME ION PUMPS GENERATE VOLTAGE ACROSS MEMBRANES
IONS CAN HAVE BOTH A CONCENTRATION (CHEMICAL) GRADIENT AND AN ELECTRIC GRADIENT (VOLTAGE)
THESE FORCES COMBINE IN THE ELECTROCHEMICAL GRADIENT, WHICH DETERMINES THE NET DIRECTION OF IONIC DIFFUSION
ELECTROGENIC PUMPS, SUCH AS SODIUM-POTASSIUM PUMPS AND PROTON PUMPS, ARE TRANSPORT PROTEINS THAT CONTRIBUTE TO ELECTROCHEMICAL GRADIENTS

13. 8.14 The Sodium - Potassium Pump

14. H.     IN COTRANSPORT, A MEMBRANE PROTEIN COUPLES THE TRANSPORT OF ONE SOLUTE TO ANOTHER
ONE SOLUTE’S “DOWNHILL” DIFFUSION DRIVES THE OTHER’S “UPHILL” TRANSPORT
8.17 CONTRANSPORT

15. I. EXOCYTOSIS AND ENDOCYTOSIS TRANSPORT LARGE MOLECULES
EXOCYTOSIS: TRANSPORT VESICLES MIGRATE TO THE PLASMA MEMBRANE, FUSE WITH IT, AND RELEASE THEIR CONTENTS
ENDOCYTOSIS: LARGE MOLECULES ENTER CELLS WITHIN VESICLES PINCHED INWARD FROM THE PLASMA MEMBRANE
PHAGOCYTOSIS
PINOCYTOSIS
RECEPTOR-MEDIATED ENDOCYTOSIS

16. 8.18 THREE TYPES OF ENDOCYTOSIS IN ANIMALS