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Cell Organelles

Cell Organelles. Cell Membrane. Controls chemical traffic in and out of the cell Selectively Permeable 8 nm thick. What is Selective Permeability?. Allows some substances to cross more easily than others Why must it be selective?.

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Cell Organelles

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  1. Cell Organelles

  2. Cell Membrane • Controls chemical traffic in and out of the cell • Selectively Permeable • 8 nm thick

  3. What is Selective Permeability? • Allows some substances to cross more easily than others • Why must it be selective?

  4. Why Must Cells Allow Some Substances to Pass Across the Membrane? • To maintain HOMEOSTASIS = • the tendency to maintain stability in an organism amid environmental change • (ability to adjust to changes) • --------------------------------------------------------- • *cells must be able to receive info, move water molecules, food particles, & ions across the membrane

  5. Membrane Structure • Synthesized in ER • sugars added in ER & Golgi

  6. Cell Membrane Synthesis • AP Bio Book Reference

  7. Membrane Structure (Con’d) • Lipid Bilayer (2 layers of phospholipids) layer #1 layer #2

  8. The Phospholipid • hydrophilic (water loving) polar heads • hydrophobic (water fearing) nonpolar tail

  9. Phospholipid Bilayer • Polar head - attracted to H2O (hydrophilic) • Nonpolar tails - push away or repel H2O (hydrophobic) • ----------------------------------------------------- • In order to best interact w/ H2O inside & outside of cell, membrane forms 2 layers of phospholipids • hydrophobic interactions hold membrane together

  10. What is allowed to easily pass through? • 1) Nonpolar (hydrophobic) molecules dissolve easily in membrane -hydrocarbons (molecules with C & H) -oxygen -(smaller molecules move faster)

  11. What can easily pass through? • 2) Polar (hydrophilic) unchargedmolecules - water, carbon dioxide

  12. What can easily pass through? • 3) Small, polar molecules - pass easilly between membrane lipids

  13. What cannot pass through easily? • Ions & large polar molecules -do not easily pass thru membrane hydrophobic area

  14. Fluid Mosaic Model • 1) Lipid Bilayer -tough but flexible • 2) Transport (channel or carrier) Proteins • 3) Receptor Proteins • 4) Marker Proteins • http://www.virtualcell.com/

  15. Lipid Bilayer (con’d) • 1) Stops large polar molecules -cannot pass thru NONPOLAR tails -thus, membrane serves as protective BARRIER

  16. Lipid Bilayer (con’d) • 2) is FLUID -not rigid -phospholipid & proteins can move laterally (rarely flip)

  17. Membrane Fluidity • Dependent on composition -unsaturated vs. saturated fatty acid tails -cholesterol

  18. Transport Proteins • Look like doughnuts in membrane surface • allow many impt. molecules & ions to cross • specific for substances they transport or translocate • like locked doors - will only let some thru

  19. Transport (Carrier) Proteins Can be carrier proteinswhich do not extend all the way thru the membrane

  20. How Carrier Proteins Work Carrier Proteins bond and drag molecule thru bilayer and release on other side

  21. Transport (Channel) Proteins Can be channel proteins that span the length of the membrane

  22. How Channel Proteins Work Molecules randomly move through by a process called diffusion

  23. Physical Structure of Transport Proteins -unilateral: embedded partway thru membrane -transmembrane: completely span membrane

  24. Types of Transport Proteins • 1) uniport: carries single solute • 2) symport: -translocates 2 different solutes -move simultaneously in same direction • 3) antiport: • exchanges 2 solutes • transports molecules in opposite directions • ex: (Na/K pump)

  25. Receptor Proteins • Shaped like boulders in membrane • convey info to inside of cell (communication) -hormones • special shape holds only certain type of molecule

  26. How Receptor Proteins Work * when molecule of right shape fits receptor protein, it causes a change at other end of receptor, triggering response in cell

  27. Receptor Proteins

  28. Marker Proteins • Look like trees sticking out of membrane • Have carbohydrates on surface • “Name Tags” of cells • Different for every individual

  29. Marker Proteins

  30. Cell-Cell Recognition • Based on recognition of cell surface macromolecules • oligosaccharides are probably important cell recognition markers - vary! • glycolipids -sugars covalently linked to lipids • glycoproteins -sugars covalently linked to proteins N-linked = asparagine O-linked = serine, threonine

  31. How can proteins which can be polar fit into nonpolar region of membrane? • Proteins made of amino acids • Of 20 aa, some polar & some nonpolar • Some aa can attract neighboring aa folding, twisting unique function

  32. Protein Variation • Allows for channel proteins - embed themselves in membrane • receptor proteins • marker proteins

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