What are the protein building structures?

The protein building structures are primarily amino acids, which are the basic units that link together to form proteins. These amino acids are connected by peptide bonds, creating polypeptide chains that fold into specific three-dimensional shapes. The sequence and arrangement of amino acids determine a protein's structure and function, which can range from enzymes to structural components in cells. Additionally, proteins can have multiple levels of structure: primary (amino acid sequence), secondary (alpha-helices and beta-sheets), tertiary (overall 3D shape), and quaternary (assembly of multiple polypeptide chains).