Switch labs are similar to previous labs, with one major exception: two target structures must be satisfied.
The first target structure is a shape that the RNA should adopt when it is alone. This is the same as the target structure in puzzles and all previous labs. The second target structure corresponds to a shape that should form when a small molecule is added.
The second target structure is less stable than the first, but it receives an energy bonus by binding the molecule of interest. The size of this bonus varies between labs.
In switch labs, the free energy of the aptamer structure must fall within a certain range of the minumum free energy structure. This is reflected in an an energy bonus for the aptamer structure. A bonus of -4.9 kcal ensures that all aptamer structures are within 4.9 kcal of the minimum free energy structure.