Nucleic acids are made up of three components: a phosphate, a sugar and a nitrogenous base. The specific building blocks of DNA and RNA are slightly different, but they fall into the same three categories.
The framework of a nucleic acid is the sugar-phosphate backbone. As the name suggests, this structure is a string of linked sugar and phosphate molecules that give the nucleic acid a "skeleton." Each individual unit of nucleic acid, called a nucleotide, contains one sugar molecule and one phosphate molecule that link to the sugars and phosphates in other nucleotides to create a chain in which sugars and phosphates alternate. Ribose is the sugar present in RNA, and deoxyribose is the sugar present in DNA.
The other part of each nucleotide is one nitrogenous base attached to the sugar molecule. The nitrogenous bases serve as the units of information in nucleic acids. There are five different nitrogenous bases, and their arrangement in a chain of DNA or RNA stores information just as an arrangement of letters makes a word. The nitrogenous bases used in DNA are adenine, thymine, cytosine and guanine. Strands of RNA contain uracil instead of thymine, but the other three bases are the same.