Four nucleotides just aren't enough these days.

DNA, the molecule underlying every form of life on this planet, is in essence a very long chain of sugar and phosphate molecules connected end to end ('long' being a relative term, of course - a molecule 5 centimeters long is gargantuan when you take into account the fact that it's only about 2.4 billionths of a meter in diameter). Each link in the chain is called a nucleotide, and is comprised of one of four possible compounds, adenine, thymine, cytosine, and guanine. Adenine bonds with thymine and cytosine to guanine; each pairing has two possible orientations, for example A-T …

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