The "special" GU pentaloop is a trick for boosting a 5-nt hairpin loop containing a GU closing pair. It is useful for solving certain puzzles with restrictions on GU and GC pairs.

How it worksEdit

The GC terminal mismatch receives a considerable bonus. In most cases, placing complementary bases as terminal mismatches results in the formation of an additional base pair. In this case, however, the triloop formed by pairing of the GC mismatch is less stable than the pentaloop.