What is DNA and how does it encode life?

DNA (deoxyribonucleic acid) is the hereditary molecule carrying biological instructions in all living cells. It's a double-helix polymer made of nucleotides, each containing one of four bases (A, T, C, G). The linear sequence of these bases forms genes – recipes for proteins – and regulatory elements. In short, DNA encodes life by specifying proteins and RNAs that perform cellular functions. For example, a gene's base sequence can determine an organism's traits (e.g. "ATCGTT…" might encode for blue eyes). DNA is replicated and passed to offspring, so life's information is preserved and "read" by cellular machinery to build and maintain organisms.