Category C - full version without watermark 720x576 (check terms and conditions at www.teledesign.de) The version with watermark is for free to embed - Description: All the many human, animal and plant proteins have one thing in common: they are built up from 21 amino acids. These amino acids like alanine, leucine, valine or glutamine are connected to long, mostly even very long chains. The different sequences of amino acids within these chain-like molecules -- the biochemist speaks of the "primary structure" -- are characteristic for the different proteins. These chains are commonly folded or twisted which results in the "secondary structure". Due to specific interactions within different parts of the molecule, often a three dimensional -- tertiary -- structure of the protein is defined.