Lec 12 MIT 7.014 Introductory Biology, Spring 2005
By the time that Watson and Crick figured out the structure of DNA, you know, it was sort of obvious that since the two strands were complimentary you could see how it replicated. And they also could see that somehow the information must be encoded in the sequence of letters down the strands of the DNA. But it wasn't obvious what the code was and how it was arranged, how it worked. And in principle it was anything you could do with four-letters. And so I pointed out the other day this was sort of a four-letter alphabet. And I think it's useful to think of it this way with A, G, C and T, and RNA as also being a four-letter alphabet. But proteins are actually a 20-letter alphabet because there are 20 different amino acids. And so somehow, since one of the key things that the DNA had to do, it somehow had to encode the information for making the proteins. And there was a lot of work on protein biosynthesis at the time. And it looked pretty complicated. People had ...