2.13: Nucleotides — libretexts.dev mirror

Nucleic acids are linear, unbranched polymers of nucleotides. Nucleotides consist of three parts.

Diagram showing molecular structures of deoxyribonucleotides and ribonucleotides, highlighting differences at the 2 carbon position: deoxyribose (H) vs ribose (OH), and linkage to bases.

A five-carbon sugar (hence a pentose). Two kinds are found:

deoxyribose, which has a hydrogen atom attached to its #2 carbon atom (designated 2'), and
ribose, which has a hydroxyl group there.

Deoxyribose-containing nucleotides, the deoxyribonucleotides, are the monomers of deoxyribonucleic acids (DNA). Ribose-containing nucleotides, the ribonucleotides, are the monomers of ribonucleic acids (RNA).

Chemical structures of adenine (A) and guanine (G) with labeled nitrogen atoms. Arrows point to NH groups, indicating the 1 attachment point for ribose sugars in nucleotide formation. Diagram showing three chemical reactions labeled A, B, and C, displaying molecular structures with red and black text for descriptions and blue labels on molecular parts.

The Purines The Pyrimidines

A nitrogen-containing ring structure called a nucleobase (or simply a base). The nucleobase is attached to the 1' carbon atom of the pentose. In DNA, four different nucleobases are found:

two purines, called adenine (A) and guanine (G)
two pyrimidines, called thymine (T) and cytosine (C)

RNA contains:

The same purines, adenine (A) and guanine (G).
RNA also uses the pyrimidine cytosine (C), but instead of thymine, it uses the pyrimidine uracil (U).

Nucleoside

The combination of a nucleobase and a pentose is called a nucleoside.

Diagram of RNA synthesis: a chain of nucleotide structures linked together, indicating the 3 and 5 ends. Labels show base, ribose, and phosphate groups with arrows indicating process direction.

One (as shown in the first figure), two, or three phosphate groups. These are attached to the 5' carbon atom of the pentose. The product in each case is called a nucleotide. Both DNA and RNA are assembled from nucleoside triphosphates.

For DNA, these are dATP, dGTP, dCTP, and dTTP.
For RNA, these are ATP, GTP, CTP, and UTP.

In both cases, as each nucleotide is attached, the second and third phosphates are removed.

Table 2.13.1: The nucleosides and their mono-, di-, and triphosphates
	Nucleobase	Nucleoside	Nucleotides
DNA	Adenine (A)	Deoxyadenosine	dAMP	dADP	dATP
	Guanine (G)	Deoxyguanosine	dGMP	dGDP	dGTP
	Cytosine (C)	Deoxycytidine	dCMP	dCDP	dCTP
	Thymine (T)	Deoxythymidine	dTMP	dTDP	dTTP
RNA	Adenine (A)	Adenosine	AMP	ADP	ATP
	Guanine (G)	Guanosine	GMP	GDP	GTP
	Cytosine (C)	Cytidine	CMP	CDP	CTP
	Uracil (U)	Uridine	UMP	UDP	UTP