Membrane Functions Cell Membranes 1. boundaries 6. Cell-cell Today’s Topics 2. Localize adhesion • Finish Cell Structure and Movement specific – Cytoskeleton functions – Motor Proteins • Membrane Structure – Fluid Mosaic 5. Cell-cell – How appropriate fluidity is maintained communication • Diffusion and Osmosis http://library.thinkquest.org/C004535/media/cell_membrane.gif 3. Transport
Sept 19, 2011 4. Signal detection
Figure 7.5 Phospholipid bilayer Fibers of extra- cellular matrix (ECM)
Glyco- Carbohydrate protein Glycolipid Fig. 7-2 EXTRACELLULAR SIDE OF MEMBRANE WATER! Hydrophilic head! Cholesterol
Microfilaments Peripheral of cytoskeleton proteins Hydrophobic Integral protein tail! CYTOPLASMIC SIDE OF MEMBRANE WATER!
Membrane Structure: The Fluid Mosaic Model
1972 Singer & Nicholson • Proteins embedded and floating in a sea hydrophobic of phospholipids A
B Phospholipid bilayer
hydrophilic
Protein and Lipid raft Figure 7.3
1 • Membrane proteins and lipids are Figure 7.6 synthesized in the ER and Golgi The Fluidity of Membranes
apparatus 1
Transmembrane glycoproteins
ER Secretory protein ~25% of known genes code for membrane Glycolipid Golgi 2 proteins apparatus
Vesicle
Most drugs target Lateral movement occurs Flip-flopping across the membrane membrane proteins !107 times per second. is rare (! once per month). 3 Plasma membrane: Cytoplasmic face 4 Extracellular face Transmembrane glycoprotein Secreted protein
Membrane glycolipid Figure 7.10
Figure 7.7 Evidence for integral membrane proteins: Evidence for membrane fluidity? Freeze-Fracture Electron Microscopy
Extracellular layer
A cell is frozen and fractured with a knife. The fracture plane often follows the hydrophobic interior of a membrane, splitting the phospholipid bilayer into two separated layers. The membrane proteins go wholly with one of the layers. Mixed proteins Knife Proteins Mouse cell after 1 hour Human cell Hybrid cell Plasma membrane Cytoplasmic layer Illustrates: asymmetry of membrane components External Leaflet Cytoplasmic Leaflet
Figure 7.4 Extracellular layer Cytoplasmic layer
Fluid Viscous
Unsaturated hydrocarbon Saturated hydro- Cholesterol tails with kinks Carbon tails
Figure 7.5 (c) Cholesterol within the animal cell membrane (b) Membrane fluidity
Figure 7.5 B
2 Figure 7.13a 1. Lipid bilayers are selectively permeable Simple Diffusion: • small,nonpolar
• small uncharged, polar
• larger uncharged, polar molecules
• ions Net diffusion Net diffusion Equilibrium (a) Diffusion of one solute Decreasing Size – polarity - ions permeability
Osmosis
Low High [Solute]! [Solute]!
H2O!
Semi- permeable membrane More Less free free water water
Osmosis!
3