Suppose that you conduct some experiments with porcine (pig) red


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Suppose that you conduct some experiments with porcine (pig) red blood cells. You suspend samples of the cells in test media of various solutes and various solute concentrations. After several experiments, you realize that an error has been made in labeling at least one of the test media. Which of the following pairs of observations convinces you that something is wrong with the media? A. The cells lysed in 0.3 M glucose and crenated (shrunk) in 0.3 M NaCl. B. The cells lysed in 0.15 M NaCl and crenated (shrunk) in 0.6 M ribose. C. The cells lysed in 0.15 M KCl and crenated (shrunk) in 0.6 M glucose. D. The cells lysed in 0.3 M glucose and crenated (shrunk) in 0.6 M ribose. E. The cells lysed in 0.25 M CaCl2 and crenated (shrunk) in 0.3 M KCl. ATTACHMENT PREVIEW Download attachment Homework_6_01-20-16.doc Biology 5A Homework 6 January 20-22, 2016 1. We know from lecture that hydrophobic interaction is the clustering of nonpolar molecules or groups together in water to minimize disruption of H-bonding between water molecules. This homework problem will help you understand how clustering reduces the disruption of water H-bonding. Water molecules are in a lower energy configuration, and thus a more thermodynamically favorable situation, when they can form a maximum number of hydrogen bonds. When methyl groups are placed in water, the adjacent water molecules are restricted in the number of hydrogen bonds they can form, because methyl groups cannot form hydrogen bonds. This restriction means that there are fewer configurations of these adjacent waters that permit hydrogen bonding. In particular, these adjacent waters must be configured so they make hydrogen bonds only towards the surrounding water, away from the methyl groups. This restricted configuration of the adjacent water molecules means that they are more ordered than they would be if the methyl group was not there. Water molecules at the interface with the methyl group thus represent a thermodynamic dilemma: These interfacial water molecules would be in a lower energy configuration if they made more hydrogen bonds, but to make the most hydrogen bonds they must assume restricted configurations that are more ordered, which is not thermodynamically favorable. The larger the area of the interface between waters and methyl groups, the larger the amount of water that is limited in its hydrogen bonding, and the more unfavorable the situation. If something can happen to reduce the amount of interface, it will be spontaneous to do so. How much interface is there along which the hydrogen bonding of water to itself is limited? Consider a simplified two-dimensional model of what happens when four methyl groups are placed in water (See accompanying figure). Let us say that the methyl groups are squares of length L along each side. The perimeter, or total length of the water-methyl interface, around each methyl group is then L x 4. When the four methyl groups are spread out and separate in the water, as in the four corners of the figure, then the total length of the interface around the four methyl groups adds up to be (L 4) 4 = 16L. If the four methyl groups cluster together as shown in the center of the figure, however, then the cluster they form has a side of length 2L, and the perimeter, or total length of the water-methyl group interface around the cluster is 2L x 4 = 8L. Thus, the clustering of the four methyl groups in this simplified two-dimensional model reduces the water-methyl group interface from 16L to 8L, and this correspondingly reduces the amount of disruption of hydrogen bonding of water to itself. Problem: Extend this two-dimension model to three dimensions. Consider a cube of methyl groups that has a length L along each edge of the cube. The area of one face of the cube is then L2, and the total area of the six faces of the cube is 6 x L 2 = 6L2. Consider now eight such cubes, first spread out and separate, and then clustered together to make one large cube. How much

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