July 22, 2011 11:35 AM

Researchers discover 2 new chemical building blocks of DNA

For decades, biology students have learned their ATGCs — a four-letter alphabet that spells out the four chemical building blocks of DNA: adenosine, thymine, guanine and cytosine. But DNA's alphabet expanded years ago. A fifth chemical building block was discovered in 1948, and a sixth in 2009.

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