Bio_Lecture_3 - Lecture 3: Biological membranes Plasma...

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Lecture 3: Biological membranes Plasma membrane Introduced phospholipids in the last section o More on phospholipids and membranes Keeps the distinction between inside and outside Membrane is both a barrier, and selective “door” to the cell Very complex regulator of cell contents “Semipermeable” barrier Questions to think about Some questions to keep in mind o What is the membrane permeable to? o What chemical properties regulate this? Size? Charge? Polarity? o What is the role of diffusion in determining cell contents? o Diffusion? When can we use it? o Can we move impermeable substances? o What is the role of H 2 O? Phospholipid Structure Phospholipids are amphipathic (hydrophilic/hydrophobic) Hydrophilic: phosphate o Orient towards water Hydrophobic: fatty acid chains o Orient away from water o Orient towards each other – hydrophobic interactions Membrane properties are dominated by the hydrophobic tails Figure 5.1b Membrane structure Physical nature of the membrane o Chemical analysis: phospholipids What is the structural arrangement? o Monolayer? (like a micelle) o Bilayer? Gorter and Grendel experiment Membrane structure experiment o Obtain a sample of RBCs from an animal Cell count o Determine the surface area of a RBC o Estimate total surface area of these cells o Isolate the phospholipids from all RBCs o Determine the surface area of a monolayer of lipids Lecture 3: Biological Membranes 1 Read pages  105-112, 143- 159, 119-137
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Compare to surface area of RBCs o Calculate the ratio Gorter and Grendel data (table) Animal #RBCs Surface area of 1 RBC Surface area of all RBCs Surface area of all lipids ratio Sheep 9,900 29.8 295,000 620,000 2.1 Rabbit 5,900 92.5 546,000 990,000 1.8 Goat 16,500 17.8 294,000 617,400 2.0 Dog 6,800 90 612,000 12,240,000 2.0 Man 4,700 99 465,000 883,500 1.9 Membrane is bilayered Allows measurement of area of monolayer Compare to estimate of RBC surface area: find = 2X RBC surface area o Have enough to cover area twice, therefore, membrane is bilayer Permeability of pure phospholipid bilayer Phospholipid bilayer should be permeable to? o
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This note was uploaded on 04/11/2011 for the course BIO 111 taught by Professor Dr. bos during the Winter '10 term at Purdue University-West Lafayette.

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Bio_Lecture_3 - Lecture 3: Biological membranes Plasma...

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