Alpha helix and beta pleated sheet is seen in
Secondary Structure: The peptide chain formed assumes a three-dimensional secondary structure by way of folding or coiling consisting of a helically-coiled, zigzag, linear or mixed form. It results from the steric relationship between amino acids located relatively near each other in the peptide chain. The linkages or bonds involved in the secondary structure formation are hydrogen bonds and disulfide bonds. Can be alpha helix or beta pleated structures.Ref: Textbook of medical biochemistry, MN Chatterji, 8th edition, page no: 89
Primary structure of protein
Secondary structure of protein
Teiary structure of protein
Quaternary structure of protein
Structure and function of protein