Question

Answer the following questions (a through f) based upon a peptide sequence with the following amino acids (one-letter symbols are given): EHSGLR

(a) What are the full names and three-letter abbreviations of the amino acids?

(b) At physiological pH, what is the best description of the chemical properties of the side chains(R groups)? (Hint: Select between nonpolar, polar uncharged, positively charged, negatively charged)

(c) Draw the structure of this peptide at pH 7.0.

(d) What is the net charge of the molecule at pH 3, 8, and 11? (Use pKa values for side chains and terminal amino and carboxyl groups as given in Table 3–1.)

(e) Estimate the pI for this peptide.

(f) What type of intermolecular force could the side chains form with water? (Note that these are interactions are with water, not with other amino acids.)

Answer 1

a) Full names of the amino acids are according to the sequence

glutamic acid- histidine- serine- glycine- leucine- arginine

Three letters abbreviations of the amino acids are according to the sequence

Glu-His-Ser-Gly-Leu-Arg

b) At physiological pH, the best description of the chemical properties of the side chain is nonpolar because in this amino acid sequence have aliphatic and aromatic side chain in histidine, glycine, leucine which is nonpolar. The acidic character of glutamic acid is neutralized by the basic chain of arginine.

c) find the attached image file

d) Net charge of the molecule at pH 3 is positive,

at pH 8 is positive

at pH 11 is negative

e) PI of the respective amino acids are in bracket and average PI of peptide is

(5.65+ 7.59+ 5.68+ 5.97+ 5.98+ 10.76) / 6 = 6.938

f) With glutamic acid water will form ionic bond

histidine- water will form ionic bond

serine- water will form hydrogen bond

glycine- water will form hydrophobic bond

leucine- water will form hydrophobic bond

arginine water will form an ionic bond.