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© Wikimedia Commons, Creative Commons Attribution-Share Alike 3.0 license. Author: Sponk, 23 March 2010.

These two molecules, RNA on the left and DNA on the right, form the basis of life as we know it. They have a remarkably simple structure, each being made of a set of four base molecules called nitrogenous bases. The bases of DNA form pairs, which attach to one another and twist into a double helix, while RNA forms a single helix. Biologists can study how DNA replicates and how the instructions contained within its molecular structure are carried out through chemical reactions in a living organism. Predicting the emergent phenomenon of life and how each organism with its own unique features arises from the structure of these molecules is far more difficult. (Unit: 9)