BIOLOGICAL ORDER 



matic function cannot be performed by different proteins. The 

 enzyme /3-galactosidase, for example, is antigenically (structurally) 

 different in bacteria, in yeasts, and in animals. One problem, the 

 hydrolysis of the ^-galactosidic link, has many solutions. The state- 

 ment that each enzyme is unique applies only to the structure of a 

 given enzyme of a given species, or group of closely related species. 

 Thus, with twenty different species of amino acids present in 

 various numbers and proportions, a practically infinite array of 

 specific proteins can be synthesized. A given organism, however, 

 synthesizes only a limited number of proteins. 



Protein Synthesis: The Code 



The hereditary information for the synthesis of proteins, with the 

 exception of some viruses, is thus contained in DNA. It seems 

 highly probable that DNA has first to manufacture an RNA 

 template and that proteins are synthesized on this template. What 

 is important is that proteins are synthesized on a nucleic acid tem- 

 plate. 



It should be added that the synthesis of a protein is an all-or-none 

 process. If only one, any one, of the amino acids entering into the 

 constitution of a protein is missing, no protein synthesis is possible. 

 An organism is apparently unable to manufacture incomplete pro- 

 teins. Things happen as if the synthesis were a sort of zipper-like 

 process, starting at one extremity of the template and continuing 

 step by step. 



Now a protein is a specific sequence of amino acids. The tem- 

 plate therefore has to be specific. How does a sequence of four 

 nucleic bases code a sequence of twenty amino acids? 



The problem of the code has been often discussed in recent years. 

 We shall closely follow Francis Crick's excellent review. If just a 

 pair of bases were enough to take care of one amino acid, the 

 number of permutations would be 16, and that is too low. If three 

 bases were required and if any set of three bases could take care 

 of one amino acid, the number of permutations would be 64. Let us 



consider a sequence of nucleic bases: ACBDACDBCAD 

 C C B A C. If we assume that the process does not start at the 



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