Leu-val-trp-asp-thr-val-arg-his-cys What is the net charge at pH 1, 5, 10, and 1
ID: 675927 • Letter: L
Question
Leu-val-trp-asp-thr-val-arg-his-cys What is the net charge at pH 1, 5, 10, and 14? Assume the following pka: carboxyl: 2.0 amino 9.0 R-SH 8.0 The answers are: for pH 1: +3 pH 5: +1 pH 10: -2 pH 14: -3 I do not know why! Any input would be greatlyappreciated. I am very confused. :( Leu-val-trp-asp-thr-val-arg-his-cys What is the net charge at pH 1, 5, 10, and 14? Assume the following pka: carboxyl: 2.0 amino 9.0 R-SH 8.0 The answers are: for pH 1: +3 pH 5: +1 pH 10: -2 pH 14: -3 I do not know why! Any input would be greatlyappreciated. I am very confused. :(Explanation / Answer
For this question, you need to list out all the pKa involved: Leu - Val - Trp - Asp - Thr - Val - Arg - His - Cys Leu: alpha -NH3+ group ( Amino pKa = 9.0,below pH 9 it will be in NH3+ state; above pH9, it will be in NH2 state) Asp: COOH group (Side chain pKa = 3.9, below pH 3.9, it will be inCOOH state; above pH 3.9, it will be in COO- state) Arg: -NH2+ group (Side chain pKa = 12.5,similar to above case) His: Side chain pKa = 6.0 Cys: alpha carboxyl pKa = 2.0, side chain pKa = 8 (as mentioned inyour question) For the following explanation, if I did not mention any residue,meaning that at that particular pH, there is no charge contributionto the structure. So, when pH = 1 Leucine residue will have +1 charge, Arginine residue will have +1charge and histidine residue will also have + 1charge. Thiscontributes total +3 charge to the overall structure. When pH = 5 Leucine residue will have +1 charge, Asp residue will have -1charge, Arginine residue will have +1 charge, histidine residuewill also have + 1charge, and Cys residue will have -1 charge. Thiscontributes a total of +1 charge to the oerall structure. When pH = 10 Asp residue will have -1 charge, Arginine residue will have +1charge, Cys residue will have -2 charge (one from COOH, one fromside chain). This contributes a total of -2 charge to the overallstructure When pH = 14, Asp residue will have -1 charge, Cys residue will have -2 charge(one from COOH, one from side chain). This contributes a total of-3 charge to the overall structure Hope this helps!
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