The Cryptographic Approach to the Problem of Protein Synthesis 65 



sequence in which red and the black cards are paired together. A heart is 

 always paired with a diainond (and vice versa), while a spade is always paired 

 with a club (and vice versa). The fact that DNA molecules also contain one 

 sugar (ribose) and one phosphate for each 'base' suggests a molecular model 

 similar to a rope ladder. The vertical ropes on both sides are formed by 'sugar- 

 phosphate- sugar-phosphate-' sequences, while the paired bases form rigid 

 horizontal steps attached to sugars on both sides. The reason why the above- 

 mentioned pairing of bases takes place is two-fold. Cytosine and thymine 

 (hearts and clubs) are 'pyrimidines', being formed by a single C — N — ring with 

 different atomic groups attached to them. Adenine and guanine (spades and 

 diamonds) are 'purines', and contain in their structure two connected rings, one 

 with six atoms, and the other with five. 



The chain shown in Fig. 1 is a sequence of sugars and phosphates. To 

 each sugar is attached a 'base', and in tliis section of the molecule you see four 

 different bases. Two of them (hearts and clubs) are short, and two others 

 (spades and diamonds) are long. Now, in order to run the second strand beside 

 it in the parallel way, we should attach short bases to long ones, and long 

 bases to short ones. Of course, in the playing card analogy again, one could 

 also join a heart to a spade and a club to a diamond. But this is excluded because 

 in these cases hydrogen atoms will be in the wrong places to form proper 

 hydrogen bonds between these two bases. 



The evidence supplied by an x-ray diffraction pattern indicates in addition 

 that the DNA molecule has a helical shape, being twisted around its central 

 axis by 36° each step. Thus, it makes a complete turn each 10 steps. 



The Watson and Crick (4) theory of dupHcation of DNA molecules proceeds 

 as follows. When the cell is ready to divide, there appears a large number of 

 free nucleotides in the nucleoplasm surrounding the chromosomes. A nucleotide 

 is defined as one of the four bases with a sugar and a phosphate attached to it. 

 At that time the double stranded DNA molecule splits into two single strands 

 along its main axis, and each strand is regenerated by catching the corresponding 

 free nucleotides from the surrounding medium. Thus, each heart separated by 

 splitting from its diamond gets another diamond from the solution, and each 

 diamond gets another heart. As the results, we get two new double stranded 

 DNA molecules, each identical with the original one. Once in a while a mistake 

 may be made in this duplication process, and we call it a mutation. So much 

 for the structure and functioning of DNA molecules. 



Now we come to the problem of information transfer from the chromosomes 

 to the enzymes. How does the sequence of bases (card suits) in DNA determine 

 the structure of the enzyme? Enzymes are proteins, and are formed by long 

 sequences of twenty different chemical groups known as amino acids. It is well 

 known that there are as many as twenty-four or twenty-five amino acids, but, 

 as Dr Yeas tells us in more detail in the next paper, one can show that the 

 extra ones in the original protein synthesis are modifications of the original 

 twenty which take place after the protein molecule is synthesized. Thus, for 

 example, 'proline' is an original amino acid used in protein synthesis, whereas 

 'hydroxyproline' is its postsynthetic modification. Since we symbolized four 

 bases of nucleic acid molecule by four playing card suits, it is reasonable to 

 symbolize the twenty basic amino acids, which have complicated chemical 



