1. Hydration

1.1 A reminder of proteins

Proteins are substances containing at least four elements (C, H, O, N); they include :

• Amino acids, basic, non-hydrolysable molecules;

• peptides, which are hydrolyzable proteins associated by peptide bonding of a small number of amino acids (less than 10 for oligopeptides and up to 50 or even 100 for polypeptides);

• proteins, which are also hydrolyzable protides. They are macromolecules of more than 100 amino acids. A distinction is made between holoproteins, which hydrolyze only amino acids, and heteroproteins, which hydrolyze amino acids plus a different fraction called the prosthetic group.

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