Homework1Solutions - BMB 461 Fall Semester 2008 Homework...

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BMB 461 Fall Semester 2008 Homework Assignment #1 Due (key posted) Thursday, September 4th Note : most of the K a and p K a values needed to solve these problems can be found in your notes or in the text. 1.) Sketch the hydrogen-bonded structures that may be formed between water and a) methanol, CH 3 OH; b) acetone; c) backbone groups on a peptide chain. O H H H O CH 3 O H H H O CH 3 O H H O C CH 3 CH 3 CH R 1 C O N H CH R 2 O H H O H H a) b) c)
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2.) Explain the forces that drive certain lipids to form micelles when mixed with water. Solution: Micelle-forming lipids are composed of a polar “head group” and long nonpolar “side chains”, that is, they are amphipathic . Water is a good solvent for the head group. The solvation of the side chain, however, is unfavorable because water molecules will maximize their hydrogen bonding by forming a partially ordered layer around the nonpolar group, decreasing the entropy of the system. If the side chains of multiple lipid molecules associate with each other, the amount of nonpolar surface exposed to water will decrease, and a smaller number of water molecules will take part in partially ordered layers, leading to a favorable increase in entropy. A micelle is one way (a bilayer is another) in which as much nonpolar surface as possible can be removed from contact with water, while the polar head groups form a hydrated “shell” around the nonpolar interior of the micelle. 3.) Calculate the concentrations of all molecular and ionic species and the pH in aqueous solutions that have the following formal compositions: a) 0.01 M acetic acid; b) 0.25 M ammonium chloride; c) 0.05 M acetic acid + 0.1 M sodium acetate; d) 0.2 M boric acid + 0.05 M sodium borate (p K a of boric acid = 9.24);
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This note was uploaded on 09/15/2008 for the course BMB 461 taught by Professor Stoltzfus during the Spring '07 term at Michigan State University.

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Homework1Solutions - BMB 461 Fall Semester 2008 Homework...

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