Group I amino acids are alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, and tryptophan. The R groups of these amino acids have either aliphatic or aromatic groups. This makes them hydrophobic (“water fearing”). In aqueous solutions, globular proteins will fold into a three-dimensional shape to bury these hydrophobic side chains in the protein interior.
Isoleucine is an isomer of leucine, and it contains two chiral carbon atoms. Proline is unique among the standard amino acids in that it does not have both free α-amino and free α-carboxyl groups. Instead, its side chain forms a cyclic structure as the nitrogen atom of proline is linked to two carbon atoms. (Strictly speaking, this means that proline is not an amino acid but rather an α-imino acid.) Phenylalanine, as the name implies, consists of a phenyl group attached to alanine. Methionine is one of the two amino acids that possess a sulfur atom. Methionine plays a central role in protein biosynthesis (translation) as it is almost always the initiating amino acid. Methionine also provides methyl groups for metabolism. Tryptophan contains an indole ring attached to the alanyl side chain.
The-linking-of-atoms-in-a-peptide-bondThe linking of atoms in a peptide bond.[Credits : Encyclopædia Britannica, Inc.]
Portion-of-polynucleotide-chain-of-deoxyribonucleic-acid-The-inset-showsPortion of polynucleotide chain of deoxyribonucleic acid (DNA). The inset shows the corresponding …[Credits : Encyclopædia Britannica, Inc.]
Red-blood-cells-trapped-in-a-mesh-of-fibrin-threadsRed blood cells (erythrocytes) trapped in a mesh of fibrin threads. The glycoprotein prothrombin, …[Credits : Eye of Science / Photo Researchers, Inc.]
Family-relationships-in-amino-acid-biosynthesesFigure 10: Family relationships in amino-acid biosyntheses. Components of proteins are underlined. …
General-scheme-of-protein-and-amino-acid-metabolismGeneral scheme of protein and amino acid metabolism.[Credits : Encyclopædia Britannica, Inc.]
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