By Harold McGee
The other influence on protein structure is the side groups of its amino acids. Because the protein chain is so long, it can bend back on itself and bring together amino acids that are some distance along the chain from each other. Amino acids with similar side groups can then bond to each other in various ways, including via hydrogen bonds, van der Waals bonds, ionic bonds, and strong covalent bonds (especially between sulfur atoms). This bonding is what gives a particular protein molecule the characteristic shape that allows it to carry out its particular job. The weak, temporary nature of the hydrogen and hydrophobic bonds allows it to change its shape as it works. The overall shape of a protein can range from a long, extended, mostly helical molecule with a few kinks or loops, to compact, elaborately folded molecules that are called “globular” proteins. Collagen is an example of a helical protein, and the various proteins in eggs are mainly globular.