Concept 1 Review

A Closer Look: Chemical Structure of a Nucleotide

The three parts of the nucleotide building block of DNA are the sugar, the base and the phosphate. The complex of the sugar with the base is called a nucleoside.

Sugar

The sugar is the 5-carbon sugar deoxyribose. By convention the carbons on this sugar are labeled 1' through 5'.

Phosphate

The phosphate is attached to the 5' carbon of the deoxyribose sugar.

Base

The base is attached to the 1' carbon of the deoxyribose sugar. There are four different bases found in DNA. Because each base contains at least two nitrogen atoms, they are called nitrogenous bases. There are two classes of bases, the pyrimidines (cytosine (C) and thymine (T)), and the purines (adenine (A) and guanine (G)).