1. Nucleotides: These are the building blocks of DNA. Each nucleotide consists of:

* A sugar molecule: This is deoxyribose in DNA.

* A phosphate group: This provides the backbone of the DNA strand.

* A nitrogenous base: There are four different nitrogenous bases in DNA:

* Adenine (A)

* Guanine (G)

* Cytosine (C)

* Thymine (T)

2. Double helix structure: Two strands of nucleotides wind around each other to form a double helix. This structure is held together by hydrogen bonds between the nitrogenous bases.

3. Base pairing: The nitrogenous bases on one strand pair up with specific bases on the other strand:

* Adenine (A) always pairs with Thymine (T)

* Guanine (G) always pairs with Cytosine (C)

In simpler terms: Imagine DNA like a twisted ladder. The sides of the ladder are made up of alternating sugar and phosphate molecules, while the rungs of the ladder are made up of pairs of nitrogenous bases. The order of these base pairs determines the genetic code that instructs the cell on how to function.