Biology · Biomolecules · NEET
Lysine is BASIC, not acidic. This trips students because the word "acid" sounds negative and lysine has no acid in its name. NCERT states clearly: acidic = glutamic acid, basic = lysine, neutral = valine. Lysine has an extra amino (-NH2) group in its R group, and extra amino groups make an amino acid basic. NEET 2020 asked exactly this: "Identify the basic amino acid" — answer Lysine.
On the NUMBER of amino (-NH2) and carboxyl (-COOH) groups in the R group (side chain). Extra -COOH groups make it acidic (glutamic acid). Extra -NH2 groups make it basic (lysine). Equal or none extra makes it neutral (valine). All amino acids already have one -NH2 and one -COOH on the alpha-carbon; the classification depends only on the extra groups in the R side chain.
Tyrosine is AROMATIC. Aromatic amino acids are a separate group named by NCERT: tyrosine, phenylalanine and tryptophan. They carry a ring (aromatic) structure in their R group. NEET 2020 listed tyrosine as one option when asking for the basic amino acid — tyrosine was the trap. Remember the three aromatic ones with "Try to Find Tyrosine" (Tryptophan, Phenylalanine, Tyrosine).
No. Serine is NOT aromatic. Serine has a hydroxy-methyl (-CH2OH) R group, which is alcoholic, not a ring. NEET 2026 tested this exact wrong statement: "Serine is an aromatic amino acid" was marked FALSE. Only tyrosine, phenylalanine and tryptophan are aromatic.
NCERT names valine as the standard example of a NEUTRAL amino acid, so for NEET always write "neutral = valine". Glycine is the simplest amino acid (its R group is just a hydrogen), but NCERT does not use glycine as the neutral example — it uses valine. Stick to the NCERT example valine to be safe in the exam.
Because its R group carries an extra carboxyl (-COOH) group. A carboxyl group can donate a proton (H+), which is acidic behaviour. Glutamic acid and aspartic acid both have an extra -COOH, so both are acidic; NCERT gives glutamic acid as the example you must remember.
Identify the basic amino acid from the following:
Which of the following 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.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Acidic (glutamic acid), basic (lysine), neutral (valine), and aromatic (tyrosine, phenylalanine, tryptophan). NCERT classifies them by the number of amino and carboxyl groups, plus a separate aromatic group with ring side chains.
Acidic = glutamic acid, Basic = lysine, Neutral = valine, Aromatic = tyrosine (also phenylalanine and tryptophan). Learn these exact names — NEET asks them directly.
Look at the R group. Extra carboxyl (-COOH) groups make it acidic. Extra amino (-NH2) groups make it basic. If neither is extra, it is neutral. The alpha-carbon always has one -NH2 and one -COOH, so only the side chain decides the type.
NCERT treats aromatic amino acids (tyrosine, phenylalanine, tryptophan) as their own group defined by a ring in the R group. For NEET, remember them as "aromatic" and do not force them into acidic/basic/neutral labels.
It is a very high-frequency, easy one-mark question in the Biomolecules chapter. NEET 2020 and NEET 2026 both asked direct recall of these examples. Memorising four names guarantees the mark.
