Please help me ! A detailed answer please! You have an unmodified peptide that h

Question

Please help me ! A detailed answer please!

You have an unmodified peptide that has an overall charge o +3 at pH 7.0 You then modified this peptide such that a lysine side chain in this peptide becomes acetylated and one amino acid side chain becomes carboxylated (this is the addition of a COOH group), what would oddi you expect the overall charge of this new, modified peptide to be at pH Briefly, explain in 2 ad sentences of less your reasoning for the overall charge of this new, modified peptide. Gue

Explanation / Answer

At a neutral pH, if the peptide has a lysine residue, the amine group on the side-chain will result in a increase in postive charge as it can be protonated at pH of 7. If the amine group is acetylated, the addition of an acetyl group increases its pKa value from the amide formation and makes it unionizable at the biological pH range thus decreasing the net positive charge which here can be estimated to go down from +3 to +2.

Next, the carobxylation of a side-chain results in the introduction of a deprotonizable carboxylate group which exists as an anion after ionization. This will result in the increase in negative charge of the peptide, Therefore the net positive charge is further decreased by the introduction of a negative charge inducing group giivng the total charge to be +1 after the aforementioned transformations to the peptide.

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