What is meant by secondary structure of proteins ?

Explanation

The secondary structure gives the manner in which polypeptide chains are folded or bent. This arises from the plane geometry of the peptide bond and hydrogen bond between one region of the backbone to another.
Pauling and Corey investigated the structures of many proteins with the help of X-rays patterns. It observed that in many proteins, polypeptide chains are coiled up in the form of a spiral staircase called helix or `alpha`- helix. The helical shape results from the formation of hydrogen bonds between amino acids in the peptid structure can be imagined as if one can coil a polypeptide chain around an invisible cylinder.
In addition, the another type of secondary structures are also known such as `beta`-pleated sheet and triple helix.