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Membranes

Membranes. Chapter 6. Outline. Phospholipid Bilayer Fluid Mosaic Model Membrane Proteins Diffusion Facilitated Diffusion Osmosis Osmotic Balance Bulk Transport Active Transport. Phospholipid Bilayer. Phospholipid has two fatty-acid chains attached to its backbone.

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Membranes

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  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

  18. 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

  19. Summary • Phospholipid Bilayer • Fluid Mosaic Model • Membrane Proteins • Diffusion • Facilitated Diffusion • Osmosis • Osmotic Balance • Bulk Transport • Active Transport

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