In this module:

Nucleotides

As mentioned on the previous page, DNA is a polymer of nucleotides. Nucleotides are assembled from the 5-carbon sugar ribose (see the Carbohydrates module for a review of sugars and other carbohydrates). If the carbons on ribose are numbered from 1' to 5', ribose is modified in three ways in nucleotides.

Click on the step numbers below to see how ribose is modified in nucleotides. Click on the mouse at left to clear the images and text.

1.

A phosphate group is attached to the hydroxyl group on the 5' carbon. Occasionally, one or two additional phosphate groups are attached to form nucleotide di- or triphosphates.

2.

One of four nitrogen-containing aromatic bases is attached to the 1' carbon by a glycosidic bond.

3.

Instead of a hydroxyl group and a hydrogen atom, the 2' carbon has two hydrogen atoms.

The four bases found in DNA are called adenine (A), thymine (T), guanine (G) and cytosine (C). The structures of these bases are shown below.

At right is a Chime structure of the nucleotide adenine. Click on the buttons below to see the ribose, the phosphate group, and the base. (If the image is too small to see at first, start by clicking the "Reset" button.)

Ribose

Phosphate

Base

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