1. Cell Membrane: Structure & Function Ms. Levensailor

2. Membrane Structure Staple ingredients of membranes are: Staple ingredients of membranes are: Lipids Lipids Proteins Proteins Phospholipids are most common Phospholipids are most common Amphipathic molecule: it has both a hydrophilic and hydrophobic region Amphipathic molecule: it has both a hydrophilic and hydrophobic region

3. Membranes are fluid Membranes are held together by hydrophobic interactions (much weaker than covalent bonds). Membranes are held together by hydrophobic interactions (much weaker than covalent bonds). They must be fluid to work properly They must be fluid to work properly When solid permeability changes & enzymatic proteins become inactive. When solid permeability changes & enzymatic proteins become inactive.

4. Membranes are mosaics of structure & function A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer. A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer.

5. Membranes are mosaics of structure & function Lipid bilayer is the main fabric of the membrane. Lipid bilayer is the main fabric of the membrane. Proteins determine most of the membrane’s functions. Proteins determine most of the membrane’s functions.

6. Membrane Carbohydrates Important in cell to cell recognition: Important in cell to cell recognition: A cell’s ability to distinguish between 1 type of neighboring cell from another. A cell’s ability to distinguish between 1 type of neighboring cell from another. i.e. identifying foreign cells (immune system) i.e. identifying foreign cells (immune system) Recognize other cells by keying in on surface molecules, carbohydrates, on the plasma membrane. Recognize other cells by keying in on surface molecules, carbohydrates, on the plasma membrane.

7. Some Functions of the membrane proteins

8. Selective Permeability Substances do not cross the barrier indiscriminately! Substances do not cross the barrier indiscriminately! Hydrophobic nonpolar molecules (hydrocarbons, carbon dioxide, & oxygen) cross with ease. Hydrophobic nonpolar molecules (hydrocarbons, carbon dioxide, & oxygen) cross with ease. Hydrophilic polar molecules (ions) are impeded by the hydrophobic core of the membrane. Hydrophilic polar molecules (ions) are impeded by the hydrophobic core of the membrane.

9. Transport Proteins Proteins built into the membrane Proteins built into the membrane Allow passage of hydrophilic substances. Allow passage of hydrophilic substances. Can be so specific that they only allow 1 specific substance to move through. Can be so specific that they only allow 1 specific substance to move through. i.e. glucose carried in blood to the human liver enters liver cells rapidly through a specific transport protein. i.e. glucose carried in blood to the human liver enters liver cells rapidly through a specific transport protein. It is so selective it rejects fructose (structural isomer of glucose). It is so selective it rejects fructose (structural isomer of glucose).

10. Passive transport Molecules have an intrinsic kinetic energy called thermal motion (heat). Molecules have an intrinsic kinetic energy called thermal motion (heat). A result of this is diffusion: A result of this is diffusion: Tendency of molecules of any substance to spread out into available space. Tendency of molecules of any substance to spread out into available space. A substance will diffuse from areas of high concentration to areas of low concentration. A substance will diffuse from areas of high concentration to areas of low concentration. Passive transport does not require energy! Passive transport does not require energy!

11. Passive Transport

12. Diffusion of one solute

13. Osmosis The passive transport of water. The passive transport of water. Hypertonic: solution with a higher concentration of solute. Hypertonic: solution with a higher concentration of solute. Hypotonic: solution with a lower solute concentration. Hypotonic: solution with a lower solute concentration. Isotonic: solutions of equal solute concentration. Isotonic: solutions of equal solute concentration.

14. Osmosis

15. Cell survival depends on water uptake & loss Cells w/out walls (animal cells) Cells w/out walls (animal cells) If cell loses water it will shrivel If cell loses water it will shrivel If cell takes up too much water it will burst If cell takes up too much water it will burst Cell w/ wall (plants & fungi) Cell w/ wall (plants & fungi) If cell takes in water the wall exerts pressure back and prevents further uptake. If cell takes in water the wall exerts pressure back and prevents further uptake. Isotonic solutions will make the plant limp. Isotonic solutions will make the plant limp. If a cell loses water it will shrivel and the plasma membrane pulls away from the wall (plasmolysis). If a cell loses water it will shrivel and the plasma membrane pulls away from the wall (plasmolysis).

16. Plasmolysis Hypotonic Hypertonic

17. Osmosis

18. Active Transport The pumping of solutes against their gradients. The pumping of solutes against their gradients. Across the plasma membrane from the side where they are less concentrated to the side where they are more concentrate. Across the plasma membrane from the side where they are less concentrated to the side where they are more concentrate. Like moving “up hill” & requires work! Like moving “up hill” & requires work! ATP supplies the energy for active transport. ATP supplies the energy for active transport. i.e. sodium-potassium pump (online activity) i.e. sodium-potassium pump (online activity)

19. Active Transport

20. Exocytosis & Endocytosis Transport large molecules (proteins & polysaccharides). Transport large molecules (proteins & polysaccharides). Exocytosis: cell secretes macromolecules by the fusion of vesicles with the plasma membrane. Exocytosis: cell secretes macromolecules by the fusion of vesicles with the plasma membrane. Endocytosis: cell takes in macromolecules by forming new vesicles from the plasma membrane. Endocytosis: cell takes in macromolecules by forming new vesicles from the plasma membrane.

21. Exocytosis & Endocytosis