1 Membranes Chapter 6

2 Outline Phospholipid Bilayer Fluid Mosaic Model Membrane Proteins Diffusion Facilitated Diffusion Osmosis – Osmotic Balance Bulk Transport Active Transport

3 Phospholipid Bilayer Phospholipid has two fatty-acid chains attached to its backbone. – One end is strongly nonpolar while the other end is strongly polar.  polar head oriented toward water and nonpolar tails oriented away from water  bilayer is stable because water’s affinity for hydrogen bonding never stops

4 Fluid Mosaic Model Plasma membrane is composed of both lipids and globular proteins. – Membrane proteins are not very soluble in water.

5 Cell Membrane Cell membrane components – phospholipid bilayer – transmembrane proteins – interior protein network – cell surface markers

6 Membrane Proteins transporters enzymes cell surface identity markers cell adhesion proteins attachments to cytoskeleton

7 Plasma Membrane Proteins

8 Membrane Protein Structure Anchoring proteins in the bilayer Transmembrane proteins – single-pass anchors – multiple-pass channels and carriers – pores

9 Passive Transport Diffusion – Random motion causes a net movement of substances from regions of high concentration to regions of low concentration.

10 Selective Membrane Transport Cell transport channels are selectively permeable, as only certain molecules are allowed to enter. – Ions cannot move between the cytoplasm of a cell and the extracellular fluid without the assistance of membrane transport proteins.  ion channels

11 Facilitated Diffusion Carriers transport ions and other solutes across the plasma membrane. – Facilitate movement by physically binding molecules on one side of the membrane, and releasing them on the other.  essential characteristics  specific  passive  saturates

12 Facilitated Diffusion

13 Osmosis In an aqueous solution, both water and solutes diffuse down concentration gradients. – Net water movement across a membrane toward a higher solute concentration by diffusion is referred to as osmosis.

14 Osmosis Osmotic concentration - concentration of all solutes in solution – Hyperosmotic - solution with the higher solute concentration – Hypoosmotic - solution with the lower solute concentration – Isosmotic - solute concentrations are equal

15 Osmotic Pressure Hydrostatic pressure - pressure of the cytoplasm pushing out against the cell membrane Osmotic pressure - pressure that must be applied to stop the osmotic movement of water across a membrane

16 Maintaining Osmotic Balance Solutions to being hypoosmotic to the environment – extrusion – isosmotic solutions – turgor

17 Bulk Transport Endocytosis - enveloping food – phagocytosis - material taken in is in particulate form – pinocytosis - material taken in is in liquid form – receptor-mediated - transport of specific molecules Exocytosis - discharge of material from vesicles at the cell surface

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19 Active Transport Active transport involves the expenditure of energy to move substance against their concentration gradient. – involves highly selective protein carriers within the membrane  sodium-potassium pump  coupled transport - using energy stored in a gradient of a different molecule

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21 Summary Phospholipid Bilayer Fluid Mosaic Model Membrane Proteins Diffusion Facilitated Diffusion Osmosis – Osmotic Balance Bulk Transport Active Transport

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