This was prepared from a large sheet cake for the bottom layer and two rounds. Arc shapes were cut from the rounds with straight pieces in between for the "bases" of the DNA. Each base (A G C or T) was given its own color. No special icing recipe just your standard Crisco powdered sugar with butter flavoring decorators icing.
Pieces were held together with icing. Tip: to decorate a cake always pair the same two colors together for accuracy. This cake was for my boss’ 60th year birthday.