Homeostasis and the Plasma Membrane: It's all about balance!

1. Chapter 5 Homeostasis & The Plasma Membrane

2. The Plasma Membrane • It’s all about balance! • Failure to adjust….death • Cells maintain balance by controlling materials entering/leaving

3. Concentrations outside the cell change • Plasma membrane must be able to maintain balance • Selective Permeability-property that allows some materials to pass through while keeping others out

4. Membrane Structure • Made of two layers made up of sheets of lipid molecules-lipid bilayer

5. Membrane Structure • Proteins are embedded in the bilayer • Think of raisins in raisin bread

6. Fluid Mosaic Model • The phospholipid bilayer acts more like a liquid than a solid.

7. The Phospholipid Bilayer

8. Most lipids have two fatty acids attached to glycerol • The third fatty acid is replaced by a phosphate group-phospholipid • Phospholipids-polar, water-soluble head + long, nonpolar, insoluble tail • Align to form double layer with “heads” on outside and “tails” on the inside

10. Diffusion • Cells maintain homeostasis by controlling the movement of substances across the membrane • Cells must use NRG to transport some substances…..Ex- Active Transport! • Other substances move across the membrane with no NRG required

11. Diffusion • Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration. • Goal of diffusion=Dynamic Equilibrium • Continuous movement with no concentration change • Concentration gradient-difference in concentration across space

12. Dynamic Equilibrium

13. Diffusion!!

14. Osmosis-Diffusion of Water • Osmosis is the diffusion of water molecules through a selectively permeable membrane • Movement from high to low concentration • Type of passive transport! • Isotonic solution-concentration of dissolved substances equal to concentration inside the cell…..NO NET MOVEMENT!

15. Isotonic Solution

16. Hypotonic vs Hypertonic • Hypotonic-solution where concentration of dissolved substances is lower than inside the cell • Water moves into cell…swelling! • Increases cell pressure-Turgor Pressure • Hypertonic-solution where concentration of dissolved substances is higher than inside the cell • Water moves out of cell…Plasmolysis

18. Dealing with Osmosis • Cells must compensate for the water that enters or exits the cell. • Animal Cells- Must maintain isotonic environment • Plant Cells- Prefer a hypotonic environment

19. Plants vs. Animals

20. Protists • Have contractile vacuoles that actively remove water from the cell.

21. Crossing the Membrane • Diffusion through ion channels: • Ion Channels- transport proteins with polar pores that ions can pass through. • Pore is the thickness of the membrane • Ion does not have touch the nonpolar interior of the bilayer.

22. Ion Channel

23. Facilitated Diffusion • Carrier proteins allow needed substances to move through membrane by binding, carrying, and releasing substances. • This movement is called facilitated diffusion

24. Facilitated Diffusion • Carrier proteins change shape using chemical energy to move particle through the membrane • Once particle is passed, original protein shape is restored

25. Facilitated Diffusion

26. Active Transport • In order to move particles from a lower concentration to higher concentration a cell must use energy…Active Transport • Proton pumps- specialized proteins for pushing different substances against the concentration gradient. • Need ATP for energy!!!!!

27. Active Transport

28. Sodium-Potassium Pump • Four Steps to the Pump: • 1. Three Na ions attach to the pump. • 2. Pump changes shape, transporting the ions across the membrane. • 3. Two K ions outside bind to the pump • 4. Two K ions are transported are released inside the cell.

29. Transport of Large Particles • Endocytosis-process in which cell surrounds and takes in material from its environment • Engulfed and enclosed by portion of cell membrane • Exocytosis-expelling wastes from interior to exterior environment

30. Endocytosis Types

31. Exocytosis