Here's why:

* DNA Structure: DNA is a double helix made up of two strands of nucleotides. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and one of four nitrogenous bases: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C).

* Base Pairing: The two strands of DNA are held together by hydrogen bonds between the bases. A always pairs with T, and G always pairs with C. This specific base pairing is crucial for storing and transmitting genetic information.

* Genetic Code: The sequence of these bases along the DNA molecule forms the genetic code. This code acts like a set of instructions that tell the cell how to build proteins, which carry out various functions within the body.

* Information Transfer: When a gene needs to be expressed, its DNA sequence is copied into RNA, a similar molecule. This RNA sequence then directs the synthesis of a specific protein.

In essence, the order of the four bases (A, T, G, C) in DNA determines the genetic information that is passed down from one generation to the next.