Biochemistry

2.4 STRUCTURE AND STRUCTURAL ORGANIZATION OF THE PROTEIN MOLECULE The polypeptide structure of proteins For a long time, scientists involved in protein chemistry have paid special attention to the relationship of amino acids in a protein molecule. The founder of Russian biochemistry A.Ya.Danilevsky at the end of the 19th century expressed interesting ideas about the structure of the protein molecule. He first pointed out the polymer nature of proteins. At the beginning of the 20th century, German biochemist E.Fischer proposed a polypeptide theory of the structure of proteins. According to this theory, amino acids are attached to each other by a covalent amide bond, which occurs when the a-carboxyl group of one amino acid reacts with the a-amino group of another amino acid. In this case, water is released. The products of this reaction are called peptides, and the link between amino acids is called peptide. Amino acid Amino acid Peptide bond Ң о II о I II- — , г-1 I II H-N-CH-C-JOH + 1 Hi-N-Cp-C-OH Amino acid: j Peptide bond R. Amino acidi R, Peptide backbone Dipeptide Peptides have a free amino group at one end and a carboxyl group at the other. New amino acids can join these groups, due to which the peptide chain builds up. 50