Question

) You have a mixture of serine, aspartic acid, and histidine. A) Find a pH value that would separateApply the sample here. the three amino acids from each other B) Draw the structure of serine, aspartic acid, and histidine at the pH chosen in part A. C) Draw how they would move in an electric field at the pH you have chosern. Apply the sample mixture here

Answer 1

ANS A. Isoelectric points of Serine,Aspartic Acid and Histidine are 5.68,2.98 and 7.60 respectively. Isoelectric point indicate that at pH equal to pI the molecule will not move under electric field because it will stay neutral. At pH above pI, the molecule will get deprtonated and acquire a -ve charge and so will move towards +ve electrode. When pH will be below pI the molecule will get protonated at N site and acquire a +ve charge and so will move towards -ve electrode.

So the ideal pH to separate all three amino acid will be 5.68 . At this pH , serine will not move, histidine will get protonated and move towards -ve electrode, and aspartic acid will get deprotonated and move towards +ve electrode.

ANS B. At pH = 5.68,

Serine HO-CH₂-CH(NH₂)-COOH Neutral

Aspartic Acid COO^--CH_2-CH(NH₂)-COO^-

Histidine

ANS C . I have already answer this at the beginning.You can draw the same and show it properly in your text.