Proteins (in literally means, proteios means of the first rank, scientist Berzelius originally gave this in the year of 1838) are large sized heteropolymeric macromolecules having one or more polypeptides or chains of sequential amino acids. The Organisation of protein levels or levels of structure consists of four major structures in a protein macromolecule, primary structure, secondary structure, tertiary structure and quaternary structure in proteins. Since, you have asked, for the secondary structure, let me give an insight for the following:
: It is the development of new stearic relationships of amino acids which are primarily present in the linear structure inside the polypeptide structure. Some of them are new in the relationships which are of regular nature and give periodicity to the given structure. There are three main types of secondary structures-- alpha helix, beta pleated and collagen helix. The alpha and beta terms are simply designating the first and the second type of secondary structures which were discovered in proteins. In alpha helix the polypeptide chain are coiled together spirally, generally in right handed manner. At places the helix is usually less regular, forming certain random coils. The helix is then stabilized by the presence of hydrogen bonds between oxygen of carboxylic group or --CO group of one amino acid residue >NH group of next or fourth amino acid residue, respectively. Actually all the main chain ---CO and >NH groups are formed due to hydrogen bonding. Alpha helical coiled secondary structure is found in several proteins, such as, keratin in hair, myosin in muscles, tropomyosin in muscles, epidermin in skin, Fibrin in blood clots. Two or more of the group, polypeptides, can further coil around each other to for, cables. This gives the structure a helical strand.