DNA serves as a genetic code by storing the instructions needed to create proteins and other essential molecules for an organism's growth and function. This information is encoded in sequences of nucleotides, which are the building blocks of DNA. These sequences are known as genes. Each gene corresponds to a specific protein or function, and the process of gene expression involves two main steps: transcription, where the DNA sequence is copied into messenger RNA (mRNA), and translation, where the mRNA is used to assemble amino acids into proteins. Thus, DNA is fundamental to heredity and the functioning of living organisms.