Lecture 19 : Proteins , Primary Struture

Proteins are polypeptide chains obtained by translation from strands of messenger RNA. The functional properties of proteins depend on their three-dimensional structures. The three-dimensional structure arises because particular sequences of amino acids in polypeptide chains fold to generate, from linear chains, compact domains with specific three-dimensional structures(Figure 19.1). Totally there are 20 different amino acids. The amino acid sequence of a protein’s polypeptide is called its primary structure. Different regions of the sequence form local regular secondary structures, such as alpha (α) helices or beta (β)strands. The tertiary structure is formed by packing such structural elements into one or several compact globular units called domains. The final protein may contain several polypeptide chains arranged in a quaternary struture. By formation of such tertiary and quaternary structure amino acids far apart in the sequence are brought close together in three dimensions to form a functional region.