This activity works as a simulation of synthetic biology by asking participants to build a molecule to interact with a specific biological target. The receptors have been made from Legos themselves or by cutting shapes into styrofoam. Usually participants are given a pile of Legos and the receptor and are tasked with building one molecule that fits completely into the receptor, meaning whatever is built has to be entirely connected together and could be taken out of the receptor in one piece. The difficulty of this activity can be increased by adding time limits, limits on brick options, using complicated receptors, blind-folding the participant, etc.
The picture shows a final ligand with receptor in the top left corner, a mutated receptor in top right, a receptor with limited bricks for ligand building in bottom left, and an empty receptor in bottom right.