What is the function of DNA in a cell?

DNA (Deoxyribonucleic Acid) is the molecule that contains the GENETIC INSTRUCTIONS for every living organism. Located primarily in the NUCLEUS of cells. STRUCTURE: Double helix — two strands wound around each other; each strand made of nucleotides with four bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C). BASE PAIRING: A pairs with T; G pairs with C. FUNCTION: Stores instructions for making proteins (via transcription → RNA → translation → protein); copied during cell division so each daughter cell receives a complete copy; mutations in DNA can cause cancer or heritable diseases. GENOME: Complete DNA sequence of an organism — human genome has ~3 billion base pairs.