English: Caption:(a) The primary structure is the sequence of amino acids that make up the

polypeptide chain. (b) The secondary structure, which can take the form of an alpha-helix or a beta-pleated sheet, is maintained by hydrogen bonds between amino acids in different regions of the original polypeptide strand. (c) The tertiary structure occurs as a result of further folding and bonding of the secondary structure. (d) The quaternary structure occurs as a result of interactions between two or more tertiary subunits. The example shown here is hemoglobin, a protein in red blood cells which transports oxygen to body tissues.

URL:https://cnx.org/contents/FPtK1zmh@8.108:Z3NTbD77@8/Organic-Compounds-Essential-to