The macromolecule that can copy itself and make proteins is DNA (deoxyribonucleic acid). DNA is a double helix structure composed of nucleotide bases: adenine (A), thymine (T), guanine (G), and cytosine (C). These bases form complementary base pairs, with A always pairing with T, and G always pairing with C. This base pairing is the basis for DNA replication, where the two strands of DNA separate, and each strand serves as a template for the synthesis of a new complementary strand. DNA also contains instructions for making proteins, which are essential for cellular structure and function. These instructions are encoded in genes, which are specific segments of DNA. The genetic code is read by cells to produce proteins through a process called protein synthesis.