Playing with LEGO® made of DNA (it follows...)

If the two molecules have complementary sequences to each other and by chance they meet, they bind specifically. Furthermore, by binding, the two flexible "cooked spaghetti" molecules form a more rigid double helix (perhaps you have also seen it represented in textbooks or on websites). In our graphic representations, dark sequences are complementary to light ones of the same color. See in the simulation below what happens when two complementary DNA molecules accidentally meet. In a solution, many DNA molecules with different sequences can be present: only the complementary ones bind themselves when they meet, the others do not interact.

(press the green flag to restart the simulations or the STOP sign to stop it).