282 ORIGIN OF STRUCTURES AND FUNCTIONS 



complementary arrangement of purine and pyrimidine mono- 

 nucleotides and polynucleotide chains is like a matrix in 

 which a particular protein can be synthesised. Each point 

 on the matrix has a specific affinity for a definite amino acid. 

 Thus, according to the hypothesis of P. C. Caldwell and C. 

 Hinshelwood,""" the amino acids crystallise, so to speak, on 

 the molecule of nucleic acid in a strictly determined order 

 corresponding with the structure of the matrix. 



As the combination of amino acids into a polypeptide 

 chain requires the expenditure of a certain amount of energy, 

 it is generally accepted that the processes leading to the 

 synthesis of proteins on nucleic acids occur in the following 

 order : 



Either the separate amino acids are activated by phos- 

 phorylation at the expense of adenosine triphosphate, or else 

 the RNA is itself phosphorylated and activated.^" The 

 amino acids are then bound to the appropriate points on 

 the nucleic acid. Later, when the full complement of amino 

 acids is present, peptide bonds are formed between them to 

 form ' pro-proteins '. Enzymes play an important part in 

 this process. When the ' pro-proteins ' have been formed they 

 become separated from the nucleic acids, a process which 

 may require a further expenditure of energy and the par- 

 ticipation of specific catalysts. This is the process which is 

 slowed down by chloramphenicol and aureomycin, substances 

 which have hardly any effect on the incorporation of amino 

 acids."'*" 



G. Gamow""^ has recently tried to use his very ingenious 

 mathematical calculations to shoAV that the specific centres for 

 the combination of particular amino acids on the nucleic 

 acid matrix consist of strictly determined groups of three 

 nucleotides. If four different nucleotides in any nucleic acid 

 are taken in groups of three, the following variants are 

 possible: (1) all three components may be the same, or, 

 to use Gamow's card-playing terminology, they may belong 

 to the same ' suit ' ; (2) two components may be the same 

 Avhile the third belongs to a different ' suit ' ; (3) all the 

 components may be different. In this way the number of 

 possible variants will be 20, which corresponds with the 

 number of amino acids in proteins. As an example, Gamow 



