Question

Amino acids are said to be amphoteric in nature because:

• A. They act as both acids as well as bases
• B. They have both primary and secondary structure
• C. They are both aliphatic and aromatic
• D. They can be essential or non-essential

Answer 1

The correct option is A They act as both acids as well as bases

Amino acids are said to be amphoteric in nature because they act as both acids as well as bases as they contain acidic COOH group and basic $N{H}_2$ group. When an amino acid is dissolved in water, at a particular pH, it exists in solution as dipolar ion or zwitterion. They can react with both acids and bases to give salts. The ionisable nature of $N{H}_2$ and COOH groups can cause them to form $N{H}_3^{+}$ and $CO{O}^{-}$ respectively.
At low pH, the carboxylic group in a zwitterion accepts a proton and becomes uncharged, so that the overall charge on the molecule is positive (cation). At high pH, a proton is released from $N{H}_3^{+}$ group of the zwitterion and becomes uncharged, so that the overall charge on the molecule is negative (anion).