pKa= 2.34 CH3CH НО. pKa 9.69) *NH3 protonated alanine a protonated amino acid %3D

Introduction to General, Organic and Biochemistry
11th Edition
ISBN:9781285869759
Author:Frederick A. Bettelheim, William H. Brown, Mary K. Campbell, Shawn O. Farrell, Omar Torres
Publisher:Frederick A. Bettelheim, William H. Brown, Mary K. Campbell, Shawn O. Farrell, Omar Torres
Chapter22: Proteins
Section: Chapter Questions
Problem 22.21P: 22-21 Explain why an amino acid cannot exist in an un-ionized form at any pH.
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A naturally occurring amino acid such as alanine has a group that is a carboxylic acid and a group that is a protonated amine. The pKa values of the two groups are shown.
(a). If the pKa value of a carboxylic acid such as acetic acid is about 5, then why is the pKa value of the carboxylic acid group of alanine so much lower? (b). Draw the structure of alanine in a solution at pH = 0.

(c). Draw the structure of alanine in a solution at physiological pH (pH 7.4).(d). Draw the structure of alanine in a solution at pH = 12.

(e). Is there a pH at which alanine is uncharged (that is, neither group has a charge)?

(f) At what pH does alanine have no net charge (that is, the amount of negative charge is the same as the amount of positive charge)?

pKa= 2.34
CH3CH
НО.
pKa 9.69)
*NH3
protonated alanine
a protonated amino acid
%3D
Transcribed Image Text:pKa= 2.34 CH3CH НО. pKa 9.69) *NH3 protonated alanine a protonated amino acid %3D
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