1. Membranes Structure and Function
Chapter 5
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3. Plasma Membrane Consists of:
* nonpolar lipid bilayer impedes the passage of water soluble substances
* degree of fluidity is determined by degree of alignment of phospholipids.
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4. Plasma Membrane Consists of:
1. Lipid bilayer
Phospholipids have a glycerol backbone with two attached fatty acid chains.
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5. Examples: small non-charged molecules, CO2, O2, glycerol, and alcohol.
Plasma Membrane is:
Selectively Permeable – meaning that it allows substances to cross the cell membrane passively
Examples: small non-charged molecules, CO2, O2, glycerol, and alcohol.
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6. * allows for passage of substances
2. Proteins
* allows for passage of substances
Mosaic of proteins float in fluid lipid bilayer.
Transmembrane Proteins
Network of Interior Proteins
Cell Surface markers
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8. Cell Membrane Proteins
Six kinds of Membrane Proteins
Transporters – channels or carriers
Enzymes – rxns. occur in interior of cell
Cell Surface Receptors – detect chem. messengers
Cell Surface Identity Markers – id cell types
Cell Adhesion Proteins – connect cells
Cytoskeleton Attachments
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9. Raven - Johnson - Biology: 6th Ed
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10. How are proteins anchored on the cell membrane?
Proteins contain polar and nonpolar regions that allow them to be anchored.
Anchoring Proteins - Attached to membrane surface.
Transmembrane Proteins
Anchor proteins
Channels and Carriers
Pores
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11. Passive Transport: Diffusion Facilitated Diffusion Osmosis
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12. Continues until equilibrium reached.
Diffusion
Random movement of substances from regions of high concentration to regions of lower concentration.(with the [gradient])
Continues until equilibrium reached.
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13. Facilitated Diffusion
Each polar molecule transported across the plasma membrane has its own type of channel protein.
Selective permeability
Ions move across membrane in ion channels.
Direction of movement determined by relative concentrations and voltage across membrane.
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14. Facilitated Diffusion
Carrier proteins facilitate movement of solutes across membrane by physically binding to them on one side of the membrane and releasing them on the other.
Driven by concentration gradients.
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15. Facilitated Diffusion
Three Essential Characteristics:
Specific
Passive
Saturates
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16. Most solutes are not lipid soluble and thus cannot cross membrane.
Osmosis
In an aqueous solution, both water and solutes diffuse down a concentration gradient.
Most solutes are not lipid soluble and thus cannot cross membrane.
Water flows through aquaporins in membrane.
Net movement of water across a membrane is termed osmosis.
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17. Osmotic Concentration - Concentration of all solutes in a solution.
Osmosis
Osmotic Concentration - Concentration of all solutes in a solution.
Hyperosmotic (Hypertonic)- Solution with higher concentration of solutes.
Hypoosmotic (Hypotonic)- Solution with lower concentration of solutes.
Isosmotic (Isotonic)- Osmotic concentrations of both solutions are the same.
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18. Osmosis
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19. Fig. 6.15
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20. Mechanisms For Maintaining Osmotic Balance Extrusion
Osmotic Pressure
Hydrostatic Pressure is caused by cytoplasm pushing out against cell membrane.
Osmotic Pressure is the pressure necessary to stop osmotic movement of water across a membrane.
Mechanisms For Maintaining Osmotic Balance
Extrusion
Isomotic Solutions
Turgor
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21. Fig. 6.16
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22. Phagocytosis - “Cell eating” Particulate form – discrete particles.
Bulk Transport:
1. Endocytosis - Plasma membrane extends outward and envelops food particles.
Phagocytosis - “Cell eating” Particulate form – discrete particles.
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23. Pinocytosis - “Cell drinking” Liquid form.
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24. Receptor-Mediated Endocytosis - Molecules first bind to specific receptors on plasma membrane before being engulfed
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25. 2 Exocytosis - Discharge of material from vesicles at cell surface; mechanism for secreting many hormones, digestive enzymes, etc.
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26. Requires input of energy.
Active Transport:
Movement of substances across a membrane against their concentration gradients.
Requires input of energy.
Enables cell to take up additional molecules of a substance already present in its cytoplasm in concentrations higher than in extracellular fluid.
Example: Sodium-Potassium Pump
moves 3 Na+ out and 2 K+ in
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29. Coupled Transport
Active transport that moves molecules coupled with sodium ions or protons down their concentration gradients (Cotransport).
Establish the down gradient.
Sodium-potassium or proton pump.
Trasverse the upgradient.
Cotransport
Symport – ex. Na+ and sugar/a.a.
Countertransport
Antiport – ex. Na+ inward and Ca++ outward
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32. Intercellular Adhesion
Cell clusters form long-lasting or permanent connections with each other (cell junctions).
The nature of the connections determines what the tissue is like.
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34. Tight junctions connect plasma membranes of adjacent cells in a sheet.
Prevent small molecules from leaking between cells and through the sheet.
Effectively segregate proteins on opposite sides of the sheet.
Fuse like a zipper
Ex. Prevent digestive enzymes from seeping into blood
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36. Hemidesmosomes - Anchor epithelial cells to basement membrane.
Anchoring Junctions
Anchoring junctions mechanically attach cytoskeleton of one cell to cytoskeleton of other cells, or to the extracellular matrix.
Desmosomes - Connect cytoskeletons of adjacent cells; prevent cells subjected to mechanical stress from pulling apart; they are buttonlike thickenings of plasma membrane
Hemidesmosomes - Anchor epithelial cells to basement membrane.
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37. Desmosomes
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38. Anchoring Junctions
Cadherins - Connect actin frameworks of cells in cadherin-mediated junctions.
Adherens - Connect actin filaments of one cell with those of neighboring cells or with extracellular matrix.
Integrin proteins
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39. Communicating Junctions
Communication junctions pass chemical signals directly from one cell to adjacent cells.
Establish direct physical connections.
Animals
Gap Junctions
Connexons.
Plants
Plasmodesmata
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41. The End
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