80mL of a 0.3M solution of hexapeptide Leu-His-Cys-Glu-Asn-Arg is adjustedto pH=pl. The solution is then titrated with 0.2M HCI to a final pH of 2.1.Sketch the titration curve, labelling the pH and volume axes. Indicate thevolume of HCl needed to reach each relevant pKa value and equivalencepoint(s). Relevant pka values are: 2.1, 4.3, 6.0, 8.3, 9.8, and 12.5.

Answered: 80mL of a 0.3M solution of hexapeptide…

Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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Question

80mL of a 0.3M solution of hexapeptide Leu-His-Cys-Glu-Asn-Arg is adjusted
to pH=pl. The solution is then titrated with 0.2M HCI to a final pH of 2.1.
Sketch the titration curve, labelling the pH and volume axes. Indicate the
volume of HCl needed to reach each relevant pKa value and equivalence
point(s). Relevant pka values are: 2.1, 4.3, 6.0, 8.3, 9.8, and 12.5.

Expert Solution

Step 1

Proteins are unbranched polymers constructed from 20 standard α-amino acids. They have four levels of structural organization. Primary structure or polypeptide is the amino acid sequence (1˚ structure), which is connected by peptide bonds. Peptide bonds are amide linkages formed between α-amino group of one amino acid and the α-carboxyl group of another amino acid. Some amino acids have side chains or R groups, which may be polar or non polar, which interact with other molecules by covalent bonding or hydrogen bonding, etc.

Here, we are titrating a hexapeptide Leu-His-Cys-Glu-Asn-Arg against HCl.