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

1. A sugar molecule: This is deoxyribose in DNA.

2. A phosphate group: This is a molecule containing phosphorus and oxygen.

3. A nitrogenous base: There are four different nitrogenous bases in DNA:

* Adenine (A)

* Thymine (T)

* Guanine (G)

* Cytosine (C)

These nucleotides are linked together to form long chains, and two of these chains twist around each other to form the double helix structure of DNA.

The order of the nitrogenous bases along the DNA chain is what determines the genetic code and ultimately the characteristics of an organism.