Amino Acid Zwitterion
At physiological pH (~7.4) glycine exists predominantly as:
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About This Question
- Subject
- chemistry
- Chapter
- biomolecules
- Topic
- amino acid zwitterion
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
Zwitterion +H3N-CH2-COO−
- Zwitterion Structure: An amino acid contains both an acidic carboxyl group (−COOH) and a basic amino group (−NH2).
- Internal Acid-Base Reaction: The carboxyl group donates a proton to the amino group, creating a dipolar ion carrying both positive and negative charges.
- pKa Values for Glycine:
- pKa1 (Carboxyl) ≈2.3
- pKa2 (Amino) ≈9.6
- 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 (−NH3+).
- State: This balanced state is the Zwitterion (+H3N−CH2−COO−). Overall charge is zero.
This easy difficulty chemistry question is from the chapter biomolecules, covering the topic of amino acid zwitterion. It appeared in the 2025 exam.
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