Animation representing the replication of DNA, the molecule that carries an organism's genome. DNA (deoxyribonucleic acid) exists as two strands of sugar-phosphate groups (grey) linked like a ladder by pairs of bases attached to the strands. There are four bases (adenine, thymine, cytosine and guanine), and each can only bind to its complementary paired base, adenine to thymine and cytosine to guanine. Due to this, one strand of DNA can be used to recreate its complementary strand. The enzyme DNA polymerase is responsible for adding complementary nucleotides (a base-sugar-phosphate group) to the growing strand, using the parent strand as a template. This is the basis for all biological heredity.