Genetic code (ATCG)

The instructions in a gene that tell the cell how to make a specific protein, A, T, C and G are the “letters” of the DNA code. They stand for the chemicals: adenine, thymine, cytosine, and guanine, respectively, that make up the nucleotide bases of DNA. Each gene’s code combines the four chemicals in various ways to spell out 3-letter “words” that specify which amino acid is needed at every step in making a protein.