Question

Name, Three-letter Symbol, and One-letter Symbol Structural Formula Residue Mass (D)6 Average Occurrence in Proteins (%) рк, C-COOH рк, Q-NH3+d Valine ÇOOCH3 99.1 6.9 2.29 9.74 Val H-C-CH. NH; CH3 a. Sketch the curve for the titration of valine with NaOH. You should begin with the fully protonated form of valine. Clearly label axes and the locations of pKas on the figure. (8 pts) b. Draw the predominate form of valine at pH 12.5. (2 pts) c. Over what pH range(s) could valine be used as an effective buffer? Explain your answer, supporting it with what we have discussed about buffers and amino acids. (4 pts)

Answer 1

The stages of deprofonation of valine orre: cool eriz (Х gooo he pe 3 CH3 р 2.29 H-C — — WH₂ pke > 2.29 WHA 9.74 Fully protonated H-&- crrez With Fully deprotonated a) Titation plot? Half equivalens (praz=9.74) o- Nwe gato e o = PH * L-cooh Half equivalence (pke; 22.29) 6) Vorm of NaOH Predominate form at 12.5 pH is: H-C-CHICH e) The buffes range of this reline is from 1 to 3 pH. The reason is that the fully protonated from is stable between this pH range.