section2_ak

section2_ak - MIT Department of Biology 7.014 Introductory...

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MIT Department of Biology 7.014 Introductory Biology, Spring 2005 Recitation Section 2 Answer Key February 7-8, 2005 Biochemistry—Molecules and Shapes Shape Game Each group has three buckets. Bucket I containes pieces of type I, bucket II—of type II, and bucket III—of type III. The goal of this game is to see how many different kinds of structures you can build from the pieces in your buckets. Each structure has to contain a piece of each type . Please remember that as you put the structures together, the color spots have to match up in the following way: Blue Red Black Silver Blue Red Black Silver 1. How many structures were you able to put together? There were 3 complete structures and a piece of type III that did not go with any of them. Three other structures can be put together, but they do not stay together as well. 2. Are all your structures identical? If not, what are the differences? Two of the structures have identical final complex shape, while the third does not. In each complex pieces of types I and II are different than in any other complex. 3. The pieces in your buckets represent three different molecules, that together work as a complex in a cell. a). What dictates whether the pieces of type I, II, and III can form a complex? The complex is put together via three-dimensional shape fitting and interactions of the chemical groups on the surface of the molecules. Interactions of the chemical groups are encoded in the colors: Blue and red—charged groups. Blue-red interactions represent ionic bonds. Black—polar groups. Black-black, black-blue, and black-red interactions represent hydrogen bonds. Silver—hydrophobic groups. Silver-silver interactions represent hydrophobic effect. The only thing you knew about each piece was its shape and coloring scheme (chemical properties). You put together complexes because they fit . In a similar sense, within a cell, two molecules interact because they can . And if they can, they do. We will return to discussing this point and its implications for the rest of this course at the end of the section.
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b). Can all pieces of type I work with all pieces of type II? If not, what are the restrictions
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section2_ak - MIT Department of Biology 7.014 Introductory...

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