2091158604

2091158604 - Examples of Selected Bond Energies...

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1 BSCI230-Lecture-6 Biomembranes and transport Chp. 4, 8 Examples of Selected Bond Energies Bond Energy = chemical energy required to break 1 mole (6x10 23 ) of bonds, expressed in calories or joules. Recall that: 1 calorie = the amount of energy required to raise 1 g of water 1 degree Centigrade (in atmosphere) • Covalent bond: 90 kcal/mole • Ionic bond: 3 " • Hydrogen bond: 1 " • van der Waals 0.1 " Approaches to Membrane Structure Studies 1. Relative impermeability to water and most large molecules 2. Separating different types of membranes 3. Chemical analysis 4. Freeze-fracture studies 5. Fluidity determinations 6. Membrane asymmetry 7. Selective permeability 8. Electrical resistance
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2 Fluidity Determination Fluorescence recovery after photobleaching Bleached area Recovery in bleached spot Example of membrane fluidity • Length of the fatty acid carbon chain • Degree of saturation, cis-bonds • Concentration of cholesterol • Reordering components within and between the lipid bilayers Factors affecting Membrane Fluidity Most Carbohydrates of Cell Membranes Exist as Glycoproteins - Face outward on plasma membrane - Covalent linkages - Common modifications of glycolipids by: N-acetylglucosamine N-acetylgalactosamine - Involvement in membrane sorting to different cellular compartments
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3 Major types of membrane lipids Glycolipids: e.g. cerebroside - amino alcohol, sugars, f. acid) Choline(+) PO 4 Glyc. Fatty Acid Phospholipids: e.g phosphatidyl choline Sterols: e.g cholesterol (polar head group) Hydrocarbon tail Polar (-) -Galactose- Cholesterol in membrane creates an intermediary fluidity by interdigitation between the phospholipids Cholesterol Phospholipid Temperature effect on lipid bilayer structure: More liquid at warmer (37C) and cooler temperature (20C) More gel-like (crystalline) at cooler temperature (20C) Cholesterol in membrane creates an intermediary fluidity Carbohydrate Modifications on Red Blood Cells - Determine Human Blood Types
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This note was uploaded on 10/22/2008 for the course BSCI 207 taught by Professor Higgins during the Spring '08 term at Maryland.

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2091158604 - Examples of Selected Bond Energies...

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