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COM 1000
Karisa Workman

Chapter 7 Membrane • Structure o Phospholipids of membranes form bilayers  They have hydrophilic/polar heads and hydrophobic/nonpolar tails (amphipathic)  Form a stable bilayer w/ head out and tail in  Hydrophobic inside prevents large or charged molecules from getting through  Phospholipids move laterally more often than vertically o Membrane is a fluid mosaic – lipids & proteins embedded in bilayer o Cholesterol (a lipid) helps stabilize animal cell membranes at different temperatures o Two major proteins in membrane  Integral/transmembrane – go all the way through the membrane; usually channels for transport  Peripheral – on surface/edge; stick up on outside of membrane o Membrane shows “sidedness”  Interior – attachment to cytoskeleton  Exterior – carbs, extracellular matrix o Glycoproteins – proteins with carbs attached; critical in cell recognition, basically ID your cells so your body knows they’re yours • Function o Organizes chemical activities of cell  Separates cell from environment  Controls what goes in/out of cell (semi-permeable)  Partitions organelle function in eukaryotes  Provides reaction surfaces and organizes enzymes and their substrates o Membrane proteins do a lot of things  Transport – act as channels/shuttles  Enzymatic activity – protein may also double as an enzyme  Signal transduction – act as receptors, which trigger cell activity when a molecular messenger binds to it  Cell recognition – glycoproteins’job  Intercellular joining – cell junctions o Diffusion across a membrane (diffusion = tendency of molecules to move from high  low concentration)  Passive – molecules diffuse down the concentration gradient; no energy required • Movement stops at equilibrium  Osmosis – passive diffusion of water • Water diffuses across membrane, not solute • More H2O than solute particles = hypotonic • Less H2O than solute particles = hypertonic • Equal distribution = isotonic • Gradient = concentration difference • Look at how cells are affecte
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