structure of proteins

Natural proteins always have a secondary and a tertiary structure, and only use natural amino acids.
  1. The primary structure of a protein is the sequence in which all those amino acids are connected within a molecule.
  2. The secondary structure of a protein is the 'helix' (see image); a spiral form of the primary structure.
  3. The tertiary structure of a protein is the way how that tertiary structure is threedimensionally folded.
  4. Sometimes there is an quaternary structure, of various packets of tertiary structure work toghether.

In the following structures you can see the primary, secundary and tertiary structure; and also the position of the 'co-enzym'.