Identify the elemental makeup of proteins.
carbon, hydrogen, and oxygen
carbon, hydrogen, and oxygen in a 1: 2: 1 ratio
carbon, hydrogen, oxygen, and nitrogen
carbon, hydrogen, oxygen, nitrogen, and phosphorus

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.