Bio Lecture Oct 6.docx

Double bonds in fatty acid chains cause a bend in the

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These differences affect membrane fluidity, ie. Double bonds in fatty acid chains cause a bend in the tail, which causes the membrane to pack loosely, making the membrane more fluid Liquid Composition of Cell Membrane o Phospholipids o Cholesterol and others Cholesterol o Composed of 4 hydrocarbon rings with a hydrophilic head composed of a hydroxyl group Sterols o Class of molecules with 4 hydrocarbon rings with different heads and tails attached to the rings Sterol in membranes of plant cells and other eukaryotic cells o Ergosterols: found in fungi and some protozoa o Phytosterols: plants o Sterols are generally absent in prokaryotes Membrane Proteins o Integral, peripheral, and glycol- proteins
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o Proportion of protein and lipid varies depending on membrane function Ie. Mitochondria it 74% protein, 24% lipids o Integral membrane proteins Proteins embedded in lipid bilayer Contains a sequence of polar and charged amino acids that are hydrophilic, with non-polar amino acids that are hydrophobic o Peripheral membrane proteins Attach on surface of membrane and do not interact with the hydrophobic core, they interact with lipid of protein by noncovalent bonds How do we know membranes are fluid? o Frye Edidin Experiment Dyed two different animal cells different colours and fused the two. The membranes started out segregated, however, over time the two membranes fused, suggesting fluid-like behavior Membrane Fluidity o Membrane bilayer is fluid o Caused by motions of lipid molecules o Fluidity affects cellular function (endocytosis, exocytosis, membrane signaling, transport) o
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  • Winter '12
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