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# An Introduction To Mechanics

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AEP 252 Problem Set #1 Due in class, Tuesday, September 9, 2008 Reading: Course packet, pages 41-60 1. Why do fatty acids commonly form bilayers? 2. Why are polar covalent bonds and the resulting permanent dipoles so important in biology? 3. Cellulose and starch are two polysaccharides with very different biological roles, yet they are constructed from identical building blocks: rings of glucose. Cellulose molecules impart stiffness and strength to plant cell walls, while starch is an important food. Which do you think is soluble, which is insoluble? Justify your answers based on the biological roles of each polysaccharide. How can polymers, built from identical building blocks, be so different? 4. Typical Bond Energies a. Using Table 3-2 on page 91 of Alberts, compute the typical bond energies of the following (in eV) i. Covalent bond ii. Ionic Bond 1. In vacuum 2. In Aqueous Environment iii. Hydrogen Bond iv. Van der Waals interaction

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Unformatted text preview: b. For comparison, compute k B T as an order-of-magnitude estimate of the thermal energy available at room temperature (25 °C). Give the answer in eV. B (Boltzmann’s constant k B = 1.38 x 10 J/K) B-23 5. a. Given below, the Henderson- Hasselbalch equation describes the relative amounts of protonated and unprotonated species that will exist in a solution at a certain pH. pH = pK +log([A-]/[HA]) Protonation and deprotonation of amino acid side chains is important for the function of many proteins. Using the values in the chart below (Biochemistry by Stryer, 2002), calculate the percentage of terminal carboxylic acid groups that would be unprotonated at pH 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. Do the same for terminal amino groups and plot that percentage as a function of pH. (This is much less tedious if you use Excel or another spreadsheet program.) b. Draw the form of a lysine amino acid that would predominate at cytosolic pH = 7....
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