Proteins are macromolecules made up of amino acids that fold into unique three-dimensional structures which determine their function. The 20 amino acids combine via peptide bonds into polypeptide chains which then fold into primary, secondary, tertiary, and sometimes quarternary structures. Secondary structures like alpha helices and beta sheets form due to hydrogen bonds between amino acids in the chain. Tertiary structure describes how secondary structure elements fold into a protein's final three-dimensional shape, which is critical for its specific biological role. Misfolded proteins can lead to diseases.