Open Question
Fill in the appropriate groups for Asp at pH 4.3.
3. Amino Acids
Zwitterion
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Which of the following molecules exists as a zwitterion at physiological pH (approximately 7.4)?
A
Methane (CH$_4$)
B
Glucose (C$_6$H$_{12}$O$_6$)
C
Sodium chloride (NaCl)
D
Glycine (NH$_2$CH$_2$COOH)
Verified step by step guidance1
Understand the concept of a zwitterion: A zwitterion is a molecule that contains both a positive and a negative charge, but is overall electrically neutral. This typically occurs in amino acids at physiological pH (around 7.4).
Analyze the structure of glycine (NH₂CH₂COOH): Glycine is an amino acid with an amino group (-NH₂) and a carboxylic acid group (-COOH). At physiological pH, the amino group is protonated to form -NH₃⁺, and the carboxylic acid group is deprotonated to form -COO⁻, resulting in a zwitterion.
Evaluate methane (CH₄): Methane is a simple hydrocarbon with no functional groups that can ionize. It cannot form a zwitterion at any pH.
Evaluate glucose (C₆H₁₂O₆): Glucose is a carbohydrate with hydroxyl (-OH) groups and an aldehyde group. It does not have functional groups that can form both positive and negative charges simultaneously, so it cannot exist as a zwitterion.
Evaluate sodium chloride (NaCl): Sodium chloride is an ionic compound that dissociates into Na⁺ and Cl⁻ in solution. It does not form a zwitterion because it is not a single molecule with both positive and negative charges within the same structure.
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