Peptide, amino acid sequence intramolecular backbone bonds

The primary structure of a protein is the sequence of the amino acid units in the protein. The secondary structure is the shape that the backbone of the molecule (the chain containing peptide bonds) assumes. The two most common secondary structures are the a-helix and the /3-pleated sheet. An a-helix is held together by the intramolecular hydrogen bonds that form between the N-H group of one amino acid and the oxygen atom in the third amino acid down the chain from it. 

---