Question

Calculate the average charge of Gly-His at pH 7.40 (pK_a = 3.5, 6.0, 9.3). (Hint: remember that the answer must be ± 0.5 of the dominant charge.)

Answer 1

Calculate the average charge of Gly-His at pH 7.40 (pKa = 3.5, 6.0, 9.3).

Answer:
                                           pKa           Charge at (pH = 7.40)
                                          
Glycein -COOH (carboxy -terminus)            `2.0                -1
Histidine   Amino-terminus (NH3+)                9.3                +1
Histidine   e-amino group                              6.00               0
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                                          Total charge = +0 (zero, no net charge)
                                          
Therefore, the net charge on the Gly-His at pH 7.40 is = 0 (zero, no net chathe)