It now seems very likely that many of the 64 triplets, possibly most of them, may code one amino acid or another, and that in general several distinct triplets may code one amino acid.
The ribosome is a machine that gets instructions from the genetic code and operates chemically in order to produce the product.
At the end of the 1970s, I was a young researcher at the Weizmann Institute with an ambitious plan to shed light on one of the major outstanding questions concerning living cells: the process of protein biosynthesis.
Ribosomes contain RNA, messenger RNA provides the information, transfer RNAs brings the amino acids; so the protein-making machinery is an RNA machinery, completely.
Much of modern molecular biology and microbiology has been based on the effort to decipher the basic code of life, which is made up of four nucleotides: adenine, thymine, cytosine, and guanine.
Many ribosomes act simultaneously along the mRNA, forming superstructures called polysomes.
Unfortunately it makes the unambiguous determination of triplets by these methods much more difficult than would be the case if there were only one triplet for each amino acid.
The meaning of this observation is unclear, but it raises the unfortunate possibility of ambiguous triplets; that is, triplets which may code more than one amino acid. However one would certainly expect such triplets to be in a minority.
DNA is a code of four letters; proteins are made up of amino acids which come in 20 forms. So the ribosome is a very clever machine that reads one language and operates in another.
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.
It now seems certain that the amino acid sequence of any protein is determined by the sequence of bases in some region of a particular nucleic acid molecule.
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.
The balance of evidence both from the cell-free system and from the study of mutation, suggests that this does not occur at random, and that triplets coding the same amino acid may well be rather similar.
