 In short, the double helix of DNA (an entity with an organization) unwinds (an activity) and new component parts (entities) bond (an activity) to both parts of the unwound DNA helix. DNA is a nucleic acid composed of several subparts: a sugar-phosphate backbone and nucleic acid bases. When DNA unwinds, the bases exhibit weak charges, properties that result from slight asymmetries in the molecules. These weak charges allow a DNA base and its complement to engage in the activity of forming hydrogen (weak polar) chemical bonds; the specificity of this activity is due to the topological arrangements of the weak polar charges in the subparts of the base. Ultimately, entities with polar charges enable the activity of hydrogen bond formation. After the complementary bases align, then the backbone forms via stronger covalent bonding. The mechanism proceeds with unwinding and bonding together (activities) new parts, to produce two helices (newly formed entities) that are (more or less faithfully) copies of the parent helix. (This process of “semi-conservative replication” and the Meselson-Stahl experiment that confirmed it are discussed in more detail in  Section 3.4.)