Amino Acids
அமினோ அமிலங்கள்
Stop memorizing structures and start looking at the alpha-carbon. If the R-group is a hydrogen, the molecule is achiral and optically inactive. NEET examiners love to trap you on Glycine's symmetry; don't fall for it.
The idea
Amino acids are organic compounds containing an amino group (-NH2) and a carboxyl group (-COOH) attached to the same alpha-carbon. They are substituted methanes where the four valency positions are occupied by hydrogen, carboxyl, amino, and a variable R-group. The nature of this R-group determines the chemical properties of the amino acid. Proteins are heteropolymers formed by the polymerization of these amino acids.
Why it matters
They serve as the fundamental monomers for protein synthesis, which are essential for structural and enzymatic functions in cells.
NEET lens
NEET focuses on the classification based on R-groups: acidic, basic, and neutral. Memorize the examples: Lysine (basic), Glutamic acid (acidic), and Valine (neutral). Expect questions on zwitterionic forms at varying pH levels. Do not confuse the alpha-carbon position with other isomers.
Clinical significance
Phenylketonuria (PKU) is a classic example of amino acid metabolism failure. A deficiency in the enzyme phenylalanine hydroxylase prevents the conversion of phenylalanine to tyrosine. This leads to toxic accumulation, causing severe intellectual disability if not managed early.
Introduction
Amino acids are the monomers of proteins. Each has a central carbon attached to: amino group (-NH₂), carboxyl group (-COOH), hydrogen (-H), and a variable R group (side chain).
Core concept
General structure: NH₂-CαH(R)-COOH. R group determines properties: nonpolar (hydrophobic, aggregate inside), polar uncharged, positively charged (at pH 7: Lys, Arg, His), negatively charged (at pH 7: Asp, Glu). 20 standard amino acids encoded by genetic code. Peptide bond: -CO-NH- formed between carboxyl of one and amino of another (condensation reaction).
Go deeper
Essential amino acids (must be obtained from diet, 8 in adults): Val, Leu, Ile, Phe, Trp, Met, Thr, Lys. Non-essential: synthesized in body. Remember: PVT TIM HALL (mnemonic) for essential AAs.
From Class 10
Proteins are made of amino acids. You know proteins are important for structure and function. Let's understand amino acid structure.