How does DNA actually carry genetic information in cells?

DNA carries genetic information through the sequence of its four chemical bases: adenine, thymine, guanine, and cytosine. These bases are attached to a sugar-phosphate backbone and pair specifically across the double helix, with adenine pairing with thymine and guanine pairing with cytosine. The precise linear order of these bases along a strand encodes instructions, much like letters spelling words. Genes are specific segments of this sequence that cells read by transcribing the DNA into messenger RNA, which then gets translated by ribosomes into proteins. The three-base codon system maps each triplet of bases to a specific amino acid, so the DNA sequence ultimately determines protein structure and function, which drives virtually all cellular activity.