Nucleotides

Nucleic acids are linear, unbranched polymers of nucleotides.

Nucleotides consist of three parts:

1.

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')
Ribose, which has a hydroxyl group atom there

Deoxyribose-containing nucleotides, the deoxyribonucleotides, are the monomers of DNA.

Ribose-containing nucleotides, the ribonucleotides, are the monomers of RNA.

2.

A nitrogen-containing ring structure called a base. The base is attached to the 1' carbon atom of the pentose. In DNA, four different bases 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).

The Pyrimidines

The Purines

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

3.

One (as shown in the first figure), two, or three phosphate groups. These are attached to the 5' carbon atom of the pentose.

Both DNA and RNA are assembled from nucleoside triphosphates.

For DNA, these are dATP, dCTP, dGTP, and dTTP.

For RNA, these are ATP, CTP, GTP, and UTP.

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

The nucleosides and their mono-, di-, and triphosphates
	Base	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

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2 September 2002