Question

C,D, and E i need help with.

17. The following peptide forms part of Human Hemoglobin subunit gammaa Asp-Leu-Lys-Gly-Thr-Phe-Ala A) Which amino acids are likely to be on the side of peptid acids are likely to be on the side of peptide that faces the interior of the protein? Insert your answer leu, Gto.Pne, Ala B) Which are likely to be facing the aqueous environment? Insert your answer Asp, lys, Thr Draw the structure of the sequence at pH7.4. Using the pka values in Table 3.1 of your textbook, make sure all lonizable groups are in their proper protonation state. Take a picture of your drawing and insert it below. Take a picture of your drawing and insert it. D) Estimate the net charge of this peptide at pH7.4. Insert your answer E) Estimate the net charge of this peptide at pH14. Insert your answer

Answer 1

Protonated and deprotonated form of amino acid depend on the pH and pKa value. If pH value is greater than the pKa the ionizable group loses its proton and remains in deprotonated form. In this peptide there are four ionizable groups two of the peptide chain, amino and carboxy terminal which are not involved in peptide bond formation and other two are side chain of the amino acid, aspartic acid and lysine.

Ans d- at pH 7.4 the charge can be calculated as

the COO- group of the C terminal (pKa= 2.34) and aspartic acid (pKa= 3.86)present in deprotonated form and contains -2 charge

the NH3+ group of N terminal and side chain of lysine is present in protonated form and contain charge +2 (+1 of amino terminal and +1 for side chain)

Total charge on peptide =-1-1+1+1 = 0

Ans e- Charge on peptide at pH =14

COO- is present in its deprotonated form as explain previously pH is greater than the pKa. Charge due to both COO- group = -1-1 =-2

NH3 group of N terminal of peptide chain also present in ionized form as pKa for NH3+ is 9.83 which is lower than the pH

Side chain of lysine is also loose its proton as pH>pKa (10.53)

So charge due to amino group is zero, total charge on protein = -2

© ph = 7.4 con 6 си иди и оии о ли и лои и cu CM UNT-c-c-N-C- C-N-C-C-N-C-C-N-C-C-EN-C-(-80-c-wo- M Tosal charge Peptide chain N Terminal +1 Peptide chain c Terminal - 1 side chain of greater aspartic and = -1 Side chain of lysine = + 1 Toralo

Charge at pu = 14 oo Nuzt wNt - Asp - Leu - Lys - Ely-The-theo-Ala-coo- at pn 14 - cool pka = 2.34 tub as coor pką of coo- of asp = 3.86 7 tnt as cool pka of Nut of peptide chain = 9.82 - present it as NH2 No charge> present as N4 pka of NH3t of Lysis = 10.53 = No charge) So the total charge on peptide =( 40 -1 +0-1) = -2 1 1 1 NH, cuo- Nu of -peptide Asp of of Lysine peptide-