1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 5: Cell Membrane Structure and Function The Fluid Mosaic Model of membrane structure describes the organization of cell membranes. – Phospholipids drift and move like a fluid. – The bilayer is a mosaic mixture of phospholipids, steroids, proteins, and other molecules.

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phospholipid Bilayer Bilayer arrangement of phospholipids makes the cell membrane selectively permeable.

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phospholipid Bilayer Cholesterol molecules embedded in the membrane keep the membrane from being too fluid or too solid.

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Fluidity of Membranes The steroid cholesterol has different effects on membrane fluidity at different temperatures: – High temps - keeps membrane from becoming too fluid – Low temps - keeps the membrane from solidifying

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Fatty Acid Composition and Fluidity of Membranes What types of organisms would you expect to have each kind of membrane fatty acids? Cold water fish Winter wheat in winter Lower leg cells of elk Most temperate plants Mammals and Birds Tropical Plants

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Membrane Proteins and Their Functions A membrane is a collage of different proteins with different functions embedded in the fluid matrix of the lipid bilayer.

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Membrane Proteins and Their Functions An overview of some major functions of membrane proteins: Transport of materials that cannot pass through the membrane passive: no energy required active: ATP energy required

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Membrane Proteins and Their Functions An overview of some major functions of membrane proteins: Enzymatic Activity Signal Transduction

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Membrane Proteins and Their Functions An overview of some major functions of membrane proteins: Cell-to-Cell Recognition Cell-to-Cell Adhesion

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why are cells so small? One micrometer (μm) is one-thousandth of a millimeter.

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why are cells so small?

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why are cells so small?

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why are cells so small?

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why are cells so small?

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why are cells so small? Surface-to-volume ratio restricts cell size by limiting transport of nutrients and wastes.

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell morphology can increase SA/V ratio

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The molecule shown A.Has a hydrophobic head (A) and hydrophilic tails (B) B.Has a hydrophilic head (A) and hydrophobic tails (B) C.Is a membrane protein D.Is a carbohydrate [Default] [MC Any] [MC All]

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Which of the following membrane proteins requires ATP for energy? A.Adhesion Proteins B.Passive Transporter Proteins C.Active Transporter Proteins D.Enzymes