Animation showing the freedom of rotation around the central carbon atom (yellow) between two planar amide groups (grey). The amide, or peptide, group (C(=O)NH) is the linkage between two amino acids in the backbone of a protein. It is a flat plane due to delocalisation of the electrons in the N-C=O group. Within each amino acid, though, the bonds are free to rotate, which makes the chain very flexible. In practice, the side chain of the amino acid (represented by the pink R) obstructs this rotation to some degree, dependent on the shape and composition of the side group. This effect is very important in determining the shape of proteins from their amino acid sequence.