In the 1950s, Francis Crick and James Watson worked together to determine the structure of DNA at the University of Cambridge, England. The phosphate residue is attached to the hydroxyl group of the 5′ carbon of one sugar of one nucleotide and the hydroxyl group of the 3′ carbon of the sugar of the next nucleotide, thereby forming a 5′-3′ phosphodiester bond. The nucleotides combine with each other by covalent bonds known as phosphodiester bonds or linkages. The sugar is deoxyribose in DNA and ribose in RNA. Each nucleotide is made up of a sugar, a phosphate group, and a nitrogenous base. Uracil (U) is also a pyrimidine (as seen in Figure 2), but it only occurs in RNA, which we will talk more about later. The nitrogenous base can be a purine, such as adenine (A) and guanine (G), or a pyrimidine, such as cytosine (C) and thymine (T). Each nucleotide is named depending on its nitrogenous base.
The important components of each nucleotide are a nitrogenous base, deoxyribose (5-carbon sugar), and a phosphate group (see Figure 2).
The building blocks of DNA are nucleotides.
