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ANNUAL REPORT SMITHSONIAN INSTITUTION, 196 2 



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English language ? Francis Crick has expressed it this way : If you 

 were to make an efficient code for encoding messages in English in the 

 liur symbols of DNA, and with this started encoding standard library 

 voi':imes of 500 pages, 500 words per page in this DNA code, you could 

 get tlia contents of 1,000 such volumes in the DNA in the nucleus of a 

 single fertilized egg cell. This is another way of saying that it requires 

 the equivalent of about 1,000 large volumes of directions in the egg 

 nucleus to sptcify that a human being like one of us will develop 

 properly from it, given a cytoplasm, proper food, and a suitable 

 environment. 



Said in another way, that is the size of a genetic recipe for building 

 a person. 



This is supposedly the way the genetic information is carried from 

 generation to generation — in a language we might call DNA-ese. 

 Each gene is a segment of DNA of perhaps three or four thousand 

 nucleotides. 



Now let us ask about the replication. The double 

 I I structure of DNA suggested immediately to Watson 



and Crick how this could happen. If, during cell di- 

 vision, the two chains were to come apart, obviously 

 each could serve as a template for picking up addi- 

 tional units to make new half chains. And this is 

 happening in each of us right now. In many cells 

 nucleotides are continually being made from food 

 components. The replication of DNA according to 

 this scheme can be illustrated as shown at the left. 



You can represent the process with j-our hands. 

 Indicate the double molecule as already directed as 

 paired hands. Take the two hands apart. Imagine 

 free fingers (nucleotides) moving around at random. 

 Each single hand serves to select in proper order the 

 one-fingered units necessary to make a complemen- 

 tary hand. The right hand is a template for making 

 a left hand and vice versa. So with a double mole- 

 cule, represented by a pair of hands, two single mole- 

 cules arise by breakage of hydrogen bonds, with 

 each then directing the synthesis of a new comple- 

 mentary single partner. 



This process of replication takes place with every 

 cell division and, as we shall see, with a high degree 

 of precision. 



This hypothesis by which two identical bipartite 

 molecules arise from a single such double molecule 

 is very satisfying in its simplicity and elegance. If 

 true, it is presumably the basis of all biological re- 



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