1. Starr & Taggart – 11 th Edition A Closer Look at Cell Membranes AP Biology: Chapter 5

2. Chapter 5 Key Concepts: Cell membrane consists of a bilayer of phospholipids and embedded proteins Transport proteins span the bilayer Open channels, gated channels, carriers, and pumps Receptor proteins receive chemical signals Recognition proteins are used for identification

3. Chapter 5 Key Concepts: Diffusion is the movement of ions from a region of higher concentration to one of lesser concentration Osmosis is the movement of water across a selectively permeable membrane to a region where its concentration is lower Some membrane proteins function in passive transport whereas some function in active transport

4. Chapter 5 Plasma Membrane Membrane is a continuous boundary layer that selectively controls the flow of substances across it Bilayer of phospholipids Hydrophilic phosphate “head” Hydrophobic “tails” of fatty acids Membrane is a Fluid-Mosaic of Phospholipids Glycolipids Sterols Proteins

5. Chapter 5 A Look at Lipids

6. Chapter 5 (cytoskeletal proteins beneath the plasma membrane) ADHESION PROTEIN open channel protein gated channel protein (open) gated channel protein (closed) active transport protein TRANSPORT PROTEINS (area of enlargement) EXTRACELLULAR ENVIRONMENT oligosaccharide groups phospholipidcholesterol RECEPTOR PROTEIN RECOGNITION PROTEIN LIPID LAYER CYTOPLASM Fluid Mosaic Model Specialized proteins and enzymes embedded in the membrane

7. Chapter 5 Fluid Mosaic Model Specialized proteins and enzymes embedded in the membrane 2 types of active transporters

8. Chapter 5 Types of Membrane Transport: Overview

9. Chapter 5 Some Terms… Concentration Gradient: the number of molecules or ions in one region is different than the number in another region in the absence of other forces, a substance moves from a region where it is more concentrated to one one where it’s less concentrated - “down” gradient Diffusion: the net movement of like molecules or ions down a concentration gradient although molecules collide randomly, the net movement is away from the place with the most collisions (down gradient) Equilibrium: when net movement stops solute concentration uniform – no gradient

10. Chapter 5 Diffusion Stepped Art

11. Chapter 5 Diffusion Stepped Art

12. Chapter 5 Factors Influencing Diffusion Rate Concentration gradient Steeper gradient=faster diffusion Molecular size Small molecules move faster Temperature Faster at higher temperatures Electric or Pressure gradient Electrical charge difference across membrane  pressure =  speed of diffusion

13. Chapter 5 Membrane Crossing Mechanisms Passive transport with concentration gradient requires no cellular energy includes diffusion, osmosis, facilitated diffusion Active transport against concentration gradient requires ATP energy includes endocytosis & exocytosis

14. Chapter 5 Selective Permeability

15. Chapter 5 How Substances Cross Cell Membranes Water soluble substances and water diffuse through channel proteins Passive and Active Transport

16. Chapter 5 Passive Transport Flow of solutes through the interior of passive transport proteins down their concentration gradients Passive transport proteins allow solutes to move both ways Does not require any energy input

17. Chapter 5 glucose transporter solute (glucose) high low Stepped Art Passive Transport

18. Chapter 5 Active Transport Net diffusion of solute is against concentration gradient Transport protein must be activated ATP gives up phosphate to activate protein Binding of ATP changes protein shape and affinity for solute

19. Chapter 5 Active Transport ATP ADP PiPi higher calcium concentration Stepped Art lower calcium concentration

20. Chapter 5 Directional Movement of Water Across Membranes Osmosis Diffusion of water due to a water concentration gradient between two regions that are separated by a selectively permeable membrane Focuses on solvent (water) movement rather than solute Osmotic movement Dependent on concentration of solutes in the water Side with more solutes has a lower concentration of water (Too large to cross the membrane) (Net movement to the right)

21. Chapter 5 Effects of Tonicity The relative solute concentrations of two fluids Isotonic Solute concentration equal on both sides of membrane No net change Hypotonic Solute concentration lower Water diffuses in Cell swells Hypertonic Solute concentration higher Water diffuses out Cell shrinks

22. Chapter 5 Effect of Tonicity on Water Movement

23. Chapter 5 Normal Cell Plasmolysis

24. Chapter 5 Pressure and Osmosis Hydrostatic pressure Pressure exerted by fluid on the walls that contain it The greater the solute concentration of the fluid, the greater the hydrostatic pressure Osmotic pressure The pressure that develops due to osmosis Amount of pressure necessary to prevent further increase of a solution’s volume

25. Chapter 5 Types of Transport: Carrier Proteins Facilitated Transport Small molecules Can’t get through membrane lipids Combine with carrier proteins Follow concentration gradient Active transport Small molecules Move against concentration gradient Combining with carrier proteins Requires energy

26. Chapter 5 Facilitated Passive Transport Solute transport through transport protein Movement is with the concentration gradient No ATP required Glucose movement in to most cells

27. Chapter 5 Active Transport ATP required Movement is against the concentration gradient Sodium-potassium pump Calcium pump

28. Chapter 5 Exocytosis and Endocytosis Exocytosis Vesicle moves to cell surface and fuses with plasma membrane Endocytosis Substances move in when plasma membrane balloons inward

29. Chapter 5 Endocytosis Phagocytosis Cell engulfs microbes, large particles, and cellular debris Amoebas and white blood cells Pinocytosis Cell “gulps” droplets of fluid. Cell usually uses the molecules dissolved in the liquid rather than the liquid itself.

30. Chapter 5 Membrane Cycling Cycling of membrane by endocytosis and exocytosis Vesicles from ER and Golgi bodies contribute Receptor proteins and lipids recycled

31. Chapter 5 In Conclusion Plasma membrane is structural and functional Cell membrane is a bilayer of lipids with proteins embedded Fluid mosaic model of cell membrane with diverse lipids and proteins within Transport proteins allow water-soluble substances to pass through membranes

32. Chapter 5 In Conclusion Receptor proteins bind substances Recognition proteins allow cells to be recognized Adhesion proteins allow cells to adhere to each other Molecules tend to move from regions of higher to lower concentration

33. Chapter 5 In Conclusion Diffusion rates are influenced by concentration gradients, temperature, molecular size, electrical charge and pressure Osmosis is the diffusion of water across a selectively permeable membrane in response to concentration gradients Water moves from hypotonic solution to a hypertonic solution

34. Chapter 5 In Conclusion Small non-polar molecules diffuse across the membrane’s bilayer Ions and polar substances move across by passive or active transport Transport proteins shunt solutes across membrane Passive transport allows movement down a concentration gradient

35. Chapter 5 In Conclusion Active transport pumps a solute across the membrane against the concentration gradient using ATP Exocytosis entails movement of a vesicle to the plasma membrane and release of particles Endocytosis entails infolding of the plasma membrane to engulf particles