What are the forces on side chains (or residues) of amino acids when they are in water?
When amino acids are joined together in proteins, only their side chains (also called radicals or residues) are left free to interact with each other and molecules of their surrounding medium (water or lipids). These side chains, therefore, have a strong influence on how the protein behaves in water. There are three forces at play between amino acids when they are not in water: 1. Van der Waals forces: the natural stickiness of each individual atom, caused by the movement of its electron cloud. While small, this effect can be substantial when two molecules can line up close to one another. 2 Electrostatic charge: the ions of a side chain that have either plus or minus charge. In a charged side chain, an atom has either lost an electron and become a positive ion or gained an electron, and becomes a negative ion. 3. S-S bonds: Several sulfur (S) – containing amino acids, such as cystein, located in the different parts of the protein chain, interact with each other, making covalent bonds
