Each ionizable group of an amino acid can exist in one of two states, charged or neutral. The electric charge on the functional group is determined by the relationship between its pKą and the pH of the solution. This relationship is described by the Henderson-Hasselbalch equation. Histidine has three ionizable functional groups. Complete the equilibrium equations by assigning the proper pKą for each ionization and the net charge on the histidine molecule in each ionization state. H || H,N*-C-C-OH H|| H,N*-C-C-o- H|| H,N*-C-C-o- H|| H,N-C-C-o- CH, CH, CH, CH, HN HN N -NH -NH -NH -NH Answer Bank pKa = 6.0 -1 pK = 9.17 +2 -2 +1 pk = 7.59 pk = 1.8 %3D 1 1

Each ionizable group of an amino acid can exist in one of two states, charged or neutral. The electric charge on the functional group is determined by the relationship between its pKą and the pH of the solution. This relationship is described by the Henderson-Hasselbalch equation. Histidine has three ionizable functional groups. Complete the equilibrium equations by assigning the proper pKą for each ionization and the net charge on the histidine molecule in each ionization state. H || H,N-C-C-OH H|| H,N-C-C-o- H|| H,N*-C-C-o- H|| H,N-C-C-o- CH, CH, CH, CH, HN HN N -NH -NH -NH -NH Answer Bank pKa = 6.0 -1 pK = 9.17 +2 -2 +1 pk = 7.59 pk = 1.8 %3D 1 1

Chemistry: Principles and Reactions

8th Edition

ISBN:9781305079373

Author:William L. Masterton, Cecile N. Hurley

Publisher:William L. Masterton, Cecile N. Hurley

Chapter23: Organic Polymers, Natural And Synthetic

Section: Chapter Questions

Problem 31QAP: On complete hydrolysis, a polypeptide gives two alanine, one leucine, one methionine, one...

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On complete hydrolysis, a polypeptide gives two alanine, one leucine, one methionine, one phenylalanine, and one valine residue. Partial hydrolysis gives the following fragments: Ala-Phe, Leu-Met, Val-Ala, Phe-Leu. It is known that the first amino acid in the sequence is valine and the last one is methionine. What is the complete sequence of amino acids?
Consider the tripeptide tyrosylleucylisoleucine. a. Specify its structure using three-letter symbols for the amino acids. b. How many peptide bonds are present within the peptide? c. Which of the amino acid residues has the largest R group? d. Which of the amino acid residues, if any, has an acidic side chain?
What special role does the amino acid cysteine have in the peptides vasopressin and oxytocin?
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For the tripeptide SerArgIle which amino acid residues a. are hydrophilic b. are hydrophobic c. possess polar neutral R groups d. participate in two amide linkages
22-21 Explain why an amino acid cannot exist in an un-ionized form at any pH.
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