It is one of the more striking generalizations of biochemistry – which surprisingly is hardly ever mentioned in the biochemical textbooks – that the twenty amino acids and the four bases, are, with minor reservations, the same throughout Nature.
For simplicity one can think of the + class as having one extra base at some point or other in the genetic message and the – class as having one too few.
Again the message to experimentalists is: Be sensible but don’t be impressed too much by negative arguments. If at all possible, try it and see what turns up. Theorists almost always dislike this sort of approach.
It would appear that the number of nonsense triplets is rather low, since we only occasionally come across them. However this conclusion is less secure than our other deductions about the general nature of the genetic code.
How is the base sequence, divided into codons? There is nothing in the backbone of the nucleic acid, which is perfectly regular, to show us how to group the bases into codons.
Trying to determine the structure of a protein by UV spectroscopy was like trying to determine the structure of a piano by listening to the sound it made while being dropped down a flight of stairs.
We are sometimes asked what the result would be if we put four +’s in one gene. To answer this my colleagues have recently put together not merely four but six +’s.
