 The player can change the sequence by placing any of the four RNA nucleotides (adenine, cytosine, guanosine and uracil) at various positions; this can alter the free energy of the system and dramatically affect the RNA strand's folding dynamics.In EteRNA, different restrictions, such as those on the number of certain bases and the number of the three base pair types, as well as locked bases, are sometimes imposed.A molecule is occasionally also included, which binds with the RNA and has critical effects on the free energy of the system.