The four types of nucleotides share a common structure composed of three main parts:

• Nitrogenous base : This is the distinguishing part of each nucleotide. The four bases are adenine (A), cytosine (C), guanine (G), and thymine (T) in DNA; in RNA, uracil (U) replaces thymine. These bases are either purines (adenine and guanine) or pyrimidines (cytosine, thymine, uracil)

• Pentose sugar : A five-carbon sugar that differs between DNA and RNA. DNA nucleotides contain deoxyribose (which lacks an oxygen atom at the 2' carbon), while RNA nucleotides contain ribose (which has a hydroxyl group at the 2' carbon). This sugar forms part of the backbone of nucleic acids

• Phosphate group : One or more phosphate groups attached to the 5' carbon of the sugar. The phosphate groups link adjacent nucleotides through phosphodiester bonds, creating the sugar-phosphate backbone of DNA and RNA

Thus, all four nucleotide types share these three parts—nitrogenous base, pentose sugar, and phosphate group—with the nitrogenous base defining the specific nucleotide type. In summary, the parts similar to the four types of nucleotides are:

• Nitrogenous base (A, T, C, G in DNA; A, U, C, G in RNA)
• Pentose sugar (deoxyribose in DNA, ribose in RNA)
• Phosphate group

These components together form each nucleotide, the building blocks of nucleic acids