Key for Practice exam #1

Key for Practice exam #1 - Practice problems for Midterm 1...

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Practice problems for Midterm 1 BIOL202S2012 1. (A) One of your classmates forgot to study their amino acid structures. Fix the errors in the structures shown below by redrawing them correctly. (B) After correcting the structure, indicate which amino acid it is, using the single letter amino acid code. (C) Classify the amino acid as either polar (uncharged), polar (charged), or nonpolar. + H 3 N C O - O C H 2 C H H 2 C CH 2 + H 3 N C O - O C CH 2 H +HN + H 3 N C O - O C CH 2 H CH CH 2 CH 3 H 3 C + H 3 N C O - O C CH 2 CH H + H 3 N C O - O C CH 2 CH 2 H A) SH CH 3 B) C) OH D) NH 2 E) + H 3 N C O - O C CH 2 C H O NH 2 N, polar uncharged + H 3 N C O - O C CH 2 H F, nonpolar + H 3 N C O - O C CH 2 H CH CH 3 H 3 C L, nonpolar (also, I, nonpolar) + H 3 N C O - O C CH 2 CH 2 H S CH 3 M, nonpolar +H 2 N CH O - O C CH 2 H H 2 C H 2 C P, nonpolar
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2. (20 pts) The structure of a zinc finger domain contains a beta-strand and an alpha- helix and looks like this: The structure is stabilized, in part, by a zinc atom which is coordinated by two cysteines contained in a loop connecting the units of secondary structure and by two histidines, one residing in the beta-strand and the other within the alpha-helix. In addition, the units of secondary structure are stabilized by noncovalent interactions. The sequence that forms this motif is: R-L-E-V-D-H-K-C-P-G-C-S-Q-H-E-T-I-A-K-N-L Loop: CPGC Strand: RLEVDHK Helix: SQHETIAKNL Identify the amino acids in the sequence that are contained in the loop, the beta- strand, and the alpha-helix. Identify the amino acids which are likely involved in the association of these two units of secondary structure (other than those involving the zinc atom). Also, identify any other amino acids that might be involved in stabilizing the individual units of secondary structure. Describe the noncovalent forces responsible for these interactions. Note that the strand and helix are amphipathic. This means that one face of the helix
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Key for Practice exam #1 - Practice problems for Midterm 1...

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