SUPPLEMENT X 



Francis H. C. Crick 

 On the genetic code 



Nobel Lecture, December 11, 1962 



Part of the work covered by the Nobel citation, that on the structure and 

 replication of DNA, has been described by Wilkins in his Nobel Lecture 

 this year. The ideas put forward by Watson and myself on the replication 

 of DNA have also been mentioned by Kornberg in his Nobel Lecture in 

 1959, covering his brilliant researches on the enzymatic synthesis of DNA 

 in the test tube. I shall discuss here the present state of a related problem in 

 information transfer in living material - that of the genetic code - which 

 has long interested me, and on which my colleagues and I, among many 

 others, have recently been doing some experimental work. 



It now seems certain that the amino acid sequence of any protein is deter- 

 mined by the sequence of bases in some region of a particular nucleic acid 

 molecule. Twenty different kinds of amino acid are commonly found in 

 protein, and four main kinds of base occur in nucleic acid. The genetic code 

 describes the way in which a sequence of twenty or more things is determined 

 by a sequence of four things of a different type. 



It is hardly necessary to stress the biological importance of the problem. 

 It seems likely that most if not all the genetic information in any organism is 

 carried by nucleic acid - usually by DNA, although certain small viruses use 

 RNA as their genetic material. It is probable that much of this information 

 is used to determine the amino acid sequence of the proteins of that organism. 

 (Whether the genetic information has any other major function we do not 

 yet know.) This idea is expressed by the classic slogan of Beadle: « one gene 

 -one enzyme », or in the more sophisticated but cumbersome terminology 

 of today: « one cistron-one polypeptide chain ». 



It is one of the more striking generalizations of biochemistry - which 

 surprisingly is hardly ever mentioned in the biochemical text-books - that 

 the twenty amino acids and the four bases, arc, with minor reservations, the 

 same throughout Nature. As fir as I am aware the presently accepted set of 

 twenty amino acids was first drawn up by Watson and myself in the summer 

 of 1953 in response to a letter of Gamow's. 



In this lecture I shall not deal with the intimate technical details of the 



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