What Is the Net Charge on the Tripeptide Gly-Arg-Lys at PH

question 58

Multiple Choice

What is the net charge on the tripeptide Gly-Arg-Lys at pH 7? The table below gives the pK_a?s of the ionizable groups on the free amino acids. $\begin{array}{|l|c|c|c|}\hline \text { Free amino acid } & \begin{array}{c}\mathrm{pKa} \text { of } \\\alpha \text {-Carboxyl group }\end{array} & \begin{array}{c}p \mathrm{k} \text { of } \\\alpha \text {-amino group }\end{array} & \begin{array}{c}\mathrm{pK} \mathrm{a} \text { of side } \\\text { chain }\end{array} \\\hline \text { Glycine } & 2.4 & 9.8 & \cdots \\\hline \text { Arginine } & 1.8 & 9.0 & 12.5 \\\hline \text { Lysine } & 2.2 & 9.1 & 10.5 \\\hline\end{array}$

• A) -1
• B) 0
• C) +1
• D) +2

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