The following is a Simulation of the Transcription Model

DNA and RNA are long, skinny molecules – almost as long as you are! 
They are formed by linking together an enormous number of smaller molecules called nucleotides. 
These nucleotides come in four varieties, denoted by their initials. The DNA nucleotides are A, T, G, and C; RNA has A, G, and C, 
but replaces T with U. Cells use DNA to make RNA. This is called transcription. Each nucleotide of RNA corresponds one 
and only one type of DNA nucleotide. Your challenge is to figure out which RNA nucleotide pairs up with which DNA nucleotide. 
Experiment with the model below. When you click the correct letter button, a nucleotide will fly up and add itself to the RNA molecule, 
but if you click the wrong button nothing will happen. 

This work is made available courtesy of the Concord Consortium under a Creative Commons Attribution 4.0 International License."