What Is the Net Charge on the Dipeptide Arg-Pro at PH

question 79

Multiple Choice

What is the net charge on the dipeptide Arg-Pro at pH 9.0? The table below gives the pKa?s of the ionizable groups on the free amino acids. $\begin{array}{|l|c|c|c|}\hline \text { Free amino acid } & \begin{array}{c}\text { pKa of } \\\alpha \text {-Carboxyl group }\end{array} & \begin{array}{c}\text { pKa of } \\\alpha \text {-amino group }\end{array} & \begin{array}{c}p \text { Ka of side } \\\text { chain }\end{array} \\\hline \text { Arginine } & 1.8 & 9.0 & 12.5 \\\hline \text { Proline } & 2.0 & 10.6 & \cdots \\\hline\end{array}$

• A) -1
• B) -0.5
• C) 0
• D) +0.5
• E) +1

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