week 4 handout answers

week 4 handout answers - Bio41 Week 4 Biochemistry Lectures...

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Bio41 Week 4 — Biochemistry Lectures 1-3 Ryan Gutierrez 1 Announcements Biochemistry Problem Set 1 due Friday, Oct. 23 at 11:59 pm. Amino acids Conjugate acids and bases
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Bio41 Week 4 — Biochemistry Lectures 1-3 Ryan Gutierrez 2 Carboxyl and amino groups in solution Below are solutions containing a carboxylic acid or amine at different pH values. For each solution, what do four representative molecules look like? Fill in the boxes. Both carboxyl and amino groups can act as buffers. Buffering is most effective when the pH is near the p K a of the group. Why? At pH = p K a , half the molecules are protonated (acids) and half are deprotonated (bases). If protons are removed from the solution, the acids will donate their protons to compensate for the loss. If protons are added to the solution, the bases will accept the extra protons. Thus pH is maintained.
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Bio41 Week 4 — Biochemistry Lectures 1-3 Ryan Gutierrez 3 Anatomy of a titration curve
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Bio41 Week 4 — Biochemistry Lectures 1-3 Ryan Gutierrez 4 Dibasic amino acids Position pH Major form(s) of alanine present Average charge on ! -carboxyl group (p K a = 2.3) Average charge on ! -amino group (p K a = 9.9) Net charge 1 <1 B 0 +1 +1 2 2.3 50% B, 50% D -0.5 +1 +0.5 3 6.1 D -1 +1 0 4 9.9 50% D, 50% C -1 +0.5 -0.5 5 ~12 C -1 0 -1 Which form of alanine is never abundant at any pH? A
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week 4 handout answers - Bio41 Week 4 Biochemistry Lectures...

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