Give a detailed account of the general structure of an amino acid, its classification on the basis of the chemical nature of the R group, the distinction between essential and non-essential amino acids, and the formation of a peptide bond between two amino acids.

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Every one of the twenty standard amino acids shares a common general structure: a central alpha-carbon bonded to four groups -- an amino group (-NH2), a carboxyl group (-COOH), a single hydrogen atom, and a fourth, variable side chain called the R group. It is this R group alone that varies from one amino acid to the next, and its chemical nature determines how the finished protein behaves. Amino acids are classified by the polarity and charge of this R group into non-polar/hydrophobic (e.g. glycine, alanine, valine), polar but uncharged (e.g. serine, threonine), acidic, carrying a negatively charged side chain (e.g. aspartic acid, glutamic acid), and basic, carrying a positively charged side chain (e.g. lysine, arginine, histidine).

A separate, nutritionally significant classification distinguishes essential amino acids, which the human body cannot synthesise in adequate amounts and must therefore obtain from food (such as leucine, lysine, valine, threonine, methionine, phenylalanine, tryptophan and isoleucine), from non-essential amino acids, which the body can synthesise for itself from other metabolic intermediates (such as glycine, alanine, serine and glutamic acid).

Amino acids link together through a peptide bond, formed by a condensation (dehydration) reaction in which the carboxyl group of one amino acid reacts with the amino group of the next, releasing one molecule of water and forming a covalent C-N bond between them. Two amino acids joined this way form a dipeptide; repeated peptide-bond formation produces a long polypeptide chain, the linear backbone from which every protein is ultimately built.

[!ANSWER]
General structure: alpha-C + NH2 + COOH + H + variable R group. R-group classes: non-polar, polar, acidic, basic. Essential (diet-required, e.g. leucine, lysine) vs non-essential (body-synthesised, e.g. glycine, alanine). Peptide bond: condensation between -COOH of one amino acid and -NH2 of next, releasing H2O.

Q.Give a detailed account of the general structure of an amino acid, its classification on the basis of the chemical nature of the R group, the distinction between essential and non-essential amino acids, and the formation of a peptide bond between two amino acids.

Concept understanding — Amino Acids

Q.Give a detailed account of the general structure of an amino acid, its classification on the basis of the chemical nature of the R group, the distinction between essential and non-essential amino acids, and the formation of a peptide bond between two amino acids.

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