Most polypeptide contain 100 – 1000 amino acids. How can one calculate the net charge of a protein at a given pH?
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Step 1: To calculate the net charge of a protein at a given pH, we need to consider the pKa values of the ionizable groups in the protein. Show more…
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2. From Amino Acids to Peptides Consider a polypeptide with the following sequence: KPYEVPAMIPES Assume the pKas of the N- and C-termini are 7.9 and 3.8, respectively, and use the pKa values on Table 1 (Table 1) for R-groups. Estimate the net charge on this molecule at pH 7 and pH 12. A. 0 (pH 7), -3 (pH 12) B. 0 (pH 7), -4 (pH 12) C. -1 (pH 7), 0 (pH 12) D. -1 (pH 7), -4 (pH 12) E. -4 (pH 7), -1 (pH 12) Table 1. Amino acid pKa values Amino Acid α-carboxylic acid α-amino Side chain Alanine 2.35 9.87 Arginine 2.01 9.04 12.48 Asparagine 2.02 8.80 Aspartic Acid 2.10 9.82 3.86 Cysteine 2.05 10.25 8.00 Glutamic Acid 2.10 9.47 4.07 Glutamine 2.17 9.13 Glycine 2.35 9.78 Histidine 1.77 9.18 6.10 Isoleucine 2.32 9.76 Leucine 2.33 9.74 Lysine 2.18 8.95 10.53 Methionine 2.28 9.21 Phenylalanine 2.58 9.24 Proline 2.00 10.60 Serine 2.21 9.15 Threonine 2.09 9.10 Tryptophan 2.38 9.39 Tyrosine 2.20 9.11 10.07 Valine 2.29 9.72
Adi S.
Calculate the net charges on the following peptides at pH=7.0. Show steps. Show individual charges on amino acids to explain how you arrived at the net charge for each of the peptides. Ala-Glu-Gly-Phe-Asp
Madhur L.
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