Tetraloops are a type of four-base hairpin loop motifs in RNA secondary structure that cap many double helices. Three types of tetraloops are common in ribosomal RNA: GNRA, UNCG and CUUG. The GNRA tetraloop has a guanine-adenine base-pair where the guanine is 5' to the helix and the adenine is 3' to the helix.

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