Secondary Structure of Proteins

Alpha helicies are held together by hydrogen bonds between the hydrogen attached to the nitrogen in the peptide bond and the oxygen attached to the carbon in a peptide bond four amino acids away on the primary amino acid chain (Fig. 1).
 

Beta sheets are held together by hydrogen bonds between the hydrogen attached to the nitrogen in the peptide bond on one strand and the oxygen attached to the carbon in a peptide bond on another sheet strand (Fig. 2).