168 NUCLEIC ACIDS, DECODING, ETC. 



ferent from the bulk of the polymer would be created. Alternative- 

 ly, it would be sufficient for a purine or pyrimidine to be missing 

 occasionally, so that at these places a deoxysugar phosphodiester 

 occurred; in this manner less stable links would be introduced at 

 which the chain could cleave via elimination or cyclization. The 

 problem of the existence of discontinuities in the DNA chains is 

 not without general interest, since these could serve to explain 

 how such a polymer, and even a circular structure, could rupture 

 at fixed and predictable positions, as has sometimes been assumed 

 in bacterial and phage genetics. 



And thirdly, and perhaps most importantly, if there really is 

 a transcription belt starting from DNA, as I have mentioned 

 before, what are the chemical mechanisms that are at play? How 

 are the precursors selected and held in place, how are nearest- 

 neighbor preferences exercised? There is a real problem in the 

 question by what forces the precursors of a polymer — nucleotides 

 or amino acids — are held onto the "template" before they are 

 polymerized enzymically. Such silly metaphors as "the zipper" 

 will not do. Anyone who has had trouble with this useful con- 

 traption knows how important the rigid aUgnment of "precur- 

 sors" is for its proper functioning. 



This brings me to the last topic I wanted to mention. Majority 

 opinion — which means, as usual, a small minority with a strong 

 voice — postulates that DNA or RNA carries a code which is, in 

 the last resort, translated into the specific amino acid sequence 

 of a protein. This code is said to be non-overlapping, composed 

 of nucleotide triplets that are read from a fixed starting point, 

 and "degenerate", i.e., several signs may have the same meaning. 

 It is also thought to be universal. 



"Code - 2. Any system of principles or rules; as, a code of 

 ethics. 3. A system of signals for communication by telegraph, 

 flags, etc.; also a system of words or other symbols arbitrarily 

 used to represent words; as, a secret code."" {Webster's New 

 Collegiate Dictionary). — Number 2, I decided, obviously does 



