字幕： The DNA double helix contains two sequences of nucleotide code letters than run along the molecule. Untwist the spiral and DNA can be seen as two parallel strands. That's why its sometimes called the double helix. Unzip the strands and you have two linear sequences of the letters A C G and T. The precise order of the letters along the molecule carries the coded instructions. These are the equivalent of binary 1s and 0s in a computer, one strand is a complementary image of the other an a will always pair with T and C with G so if you know the sequence of one strand you can work out the sequence of the other. It dawned on Watson and Crick that this complementary copy of the code was the key to understanding how genetic information could be passed on. So the essence of life could be explained with chemistry, there were no mysterious life forces.