DNA is made up of nucleotides. Each nucleotide consists of three parts:

* A sugar molecule called deoxyribose

* A phosphate group

* A nitrogenous base

There are four different nitrogenous bases in DNA:

* Adenine (A)

* Guanine (G)

* Cytosine (C)

* Thymine (T)

These nucleotides are linked together in a long chain, forming a double helix structure. The two strands of the helix are held together by hydrogen bonds between the nitrogenous bases. Adenine always pairs with thymine (A-T), and guanine always pairs with cytosine (G-C).