Which amino acid substitution would result in the greatest change in the net charge of a polypeptide at pH 7?A.Glu to LysB.Asp to AlaC.Lys to ArgD.Arg to Ser

The net charge of a polypeptide at pH 7 is determined by the ionizable side chains of the amino acids that make up the polypeptide.

Amino acids can be classified into different groups based on the properties of their side chains. Some amino acids have side chains that can carry a positive or negative charge, depending on the pH of the solution.

At pH 7:

• Glutamic acid (Glu) carries a negative charge.
• Lysine (Lys) carries a positive charge.
• Aspartic acid (Asp) carries a negative charge.
• Alanine (Ala) is neutral.
• Arginine (Arg) carries a positive charge.
• Serine (Ser) is neutral.

Now, let's analyze the substitutions:

A. Glu to Lys: This substitution changes a negatively charged amino acid to a positively charged one. This would result in a change of 2 units in the net charge (+1 from removing the negative charge of Glu and +1 from adding the positive charge of Lys).

B. Asp to Ala: This substitution changes a negatively charged amino acid to a neutral one. This would result in a change of 1 unit in the net charge (+1 from removing the negative charge of Asp).

C. Lys to Arg: Both of these amino acids carry a positive charge, so this substitution would not change the net charge.

D. Arg to Ser: This substitution changes a positively charged amino acid to a neutral one. This would result in a change of 1 unit in the net charge (-1 from removing the positive charge of Arg).

Therefore, the substitution that would result in the greatest change in the net charge of a polypeptide at pH 7 is A. Glu to Lys.