Ionizable Groups & pH Effects on Amino Acids — NEET Biology
✅ Asked in NEET 2026The chemical and physical properties of amino acids are essentially of the amino, carboxyl and the R functional groups. Based on number of amino and carboxyl groups, there are acidic (e.g., glutamic acid), basic (lysine) and neutral (valine) amino acids. Similarly, there are aromatic amino acids (tyrosine, phenylalanine, tryptophan). A particular property of amino acids is the ionizable nature of –NH₂ and –COOH groups. Hence in solutions of different pH, the structure of amino acids changes.
NTA tests how amino acids change structure at different pH values because their –NH₂ and –COOH groups are ionizable. Students often forget that at physiological pH, both groups exist in ionized forms, and the isoelectric point (pI) is where the net charge is zero. The common mistake is confusing the ionizable nature with the classification of amino acids—remembering that acidity/basicity depends on the R group, not just the terminal groups. To score correctly: know that at low pH the molecule gains protons (becomes positive), at high pH it loses protons (becomes negative), and at pI the charges balance. This concept appears repeatedly because it's fundamental to protein structure and function in NEET.
This paragraph was tested 3 times in NEET.
Which statements are correct regarding amino acids? A. They are substituted methanes. B. Serine is an aromatic amino acid. C. Valine is a neutral amino acid. D. Lysine is an acidic amino acid.
The following can be found as a zwitter ion:
Identify the basic amino acid from the following: (NEET 2020)
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