Video narration
How can a twisted ladder carry the instructions for inheritance-and how did scientists know it was DNA, not protein? Think of DNA as a recipe written in chemistry. Its double helix has two strands held together by matching base pairs. The order of those bases stores information, and pairing lets each strand guide a copy. But shape alone was not proof. First, bacteria gained a heritable trait when material from other bacteria entered them. That showed an inherited instruction could move between cells. Later, scientists isolated DNA: destroying it stopped the change, while destroying protein did not. Then bacteriophage experiments tracked what entered infected bacteria. DNA went in and directed production of new viruses. The clues became convincing. DNA is the genetic material because changing or delivering it changed inherited traits, while protein did not. Its structure stores instructions, and experiments showed it entering cells.