Pyrimidine Moieties in Animals, Plants, and Bacteria 83 



triplet of Equation 1 to T in the second triplet of Equation 2), 

 only one amino acid in the resulting protein chain will be altered; 

 that is, the amino acid coded by TGT replaces the amino acid 

 coded by TGC. The protein with the changed amino acid may 

 still be functional or partly functional. 



If a nucleotide base is deleted following nitrogen mustard or 

 proflavin treatment, the gene is inactivated. In Equation 3, it is 

 seen that G has been deleted from the second triplet of Ecjuation 1. 

 With a nonoverlapping code, the second triplet now becomes 

 TCT, the third triplet becomes GCT, etc. In other words, all 

 triplets from TCT on are changed. Thus, all amino acids in the 

 protein chain which are coded by the second triplet to the last 

 triplet are changed, and the new protein chain cannot function. 

 As a result, the gene controlling the synthesis of that protein has 

 been inactivated. 



For a more detailed discussion of mutation mechanisms at the 

 chemical level, the reader is referred to the papers of Freese (21), 

 Lawley (41) and Crick et al. (13). 



It is apparent that a knowledge of the number of DNA molecules 

 in a given cell and of the entire nucleotide sequence of each mole- 

 cule, along with the code by which DNA and RNA sequences are 

 translated to the amino acid sequences of proteins, would suffice as a 

 "blue print" for describing any organism. Such a total description 

 is, of course, not available to us as yet. We do, however, know cer- 

 tain characteristics of the DNA of many species of bacteria, plants, 

 animals, and viruses. The amount of DNA per cell is known in many 

 instances. This, in a sense, tells us how "thick" each "genetic book 

 of instructions" is. We also have knowledge of the average nucleo- 

 tide composition of the DNA of different species, that is, of how fre- 

 quently the "alphabet symbols" are repeated in each book. There is 

 also some knowledge of the range of composition within a particular 

 cell. These topics will be discussed in the second section of this 

 paper. 



In the third section of this paper, I shall consider the composition 

 of RNA molecules and the proposed mechanisms for transcribing 

 information from DNA to RNxA. Finally, I shall briefly touch on 

 the translation of the DNA-RNA code to amino acid sequences 

 of proteins. 



