The player has to build a complete RNA string around a randomly given DNA cycle such that each pairing fits well. The admissible pairings are A-T, C-G, G-C, and U-A.
 
The player can take RNA molecules - one per round - from a small heap. The selected nucleotide is added to one of the two ends of the initial RNA string. A randomly acting Provider refills the heap after each move. Because of the Provider's randomness the player can not plan completely deterministically. Like in Scrabble, it is often a rather good strategy to keep a "mixed heap".
 
Warning: When you are familiar with the biological process, you know that in nature the RNA strings are NOT built by adding bases to both ends of the initial string in arbitrary order. So, this puzzle is not suited for learning the chemical/biological process! By playing the RNA-Puzzle you will probably learn more about discrete stochastics than about biology...
 
The puzzle may be played with Zillions on a computer monitor. But you may also do it in a more traditional way with a set of 52 cards.