Amino Acid Zwitterion

Question

At physiological pH (~7.4) glycine exists predominantly as:

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1. **Zwitterion Structure**: An amino acid contains both an acidic carboxyl group ($-COOH$) and a basic amino group ($-NH_2$).
2. **Internal Acid-Base Reaction**: The carboxyl group donates a proton to the amino group, creating a dipolar ion carrying both positive and negative charges.
3. **pKa Values for Glycine**:
   - $pKa_1$ (Carboxyl) $\approx 2.3$
   - $pKa_2$ (Amino) $\approx 9.6$
4. **pH Influence**: At physiological pH ($7.4$), the environment is basic enough to keep the carboxyl group deprotonated ($-COO^-$) but acidic enough to keep the amino group protonated ($-NH_3^+$).
5. **State**: This balanced state is the **Zwitterion** ($^+H_3N-CH_2-COO^-$). Overall charge is zero.

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Amino Acid Zwitterion

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