Biology – 4.1 Biological molecules | e-Consult

Proteins are primarily composed of the elements carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). Sulfur (S) is also commonly found in proteins, particularly in the amino acids cysteine and methionine. The arrangement of these elements is incredibly diverse, stemming from the sequence of amino acids linked together by peptide bonds. This sequence determines the protein's primary structure. The folding of the polypeptide chain into secondary (alpha-helices and beta-sheets), tertiary (3D structure), and quaternary (multiple polypeptide chains) structures is dictated by various interactions between the atoms (e.g., hydrogen bonds, ionic bonds, disulfide bridges). This complex arrangement of atoms is what gives proteins their diverse three-dimensional shapes, which in turn determines their specific functions – such as enzymes catalyzing reactions, antibodies recognizing antigens, and structural proteins providing support.