THE HEREDITARY ORDER: GENETIC INFORMATION 



glutamic acid is replaced by valine. In hemoglobin C, glutamic 

 acid is replaced by lysine. 



Thus we have learned that nucleic acid is the substrate of heredi- 

 tary properties, and that the genes control the synthesis of specific 

 proteins, or of specific enzymes. We know that the sequence of 

 nucleic bases in the genetic material is responsible for the sequence 

 of amino acids in the proteins. We know that the replacement of one 

 base pair by another may be responsible for a mutation. We also 

 know that the difference between the normal and the mutated 

 protein may be due to the replacement of one amino acid by an- 

 other. As a consequence of the replacement of one base pair by 

 another in the gene, one amino acid is replaced by another in the 

 protein. The sequence is changed, and as a consequence the folding 

 of the polypeptide chain might be changed too. The nucleic acid, 

 the genetic material, is the substrate of the structural, hereditary 

 change. The protein is the agent through which the hereditary 

 change is expressed. 



Reproduction of the 

 Genetic Material 



DNA. The genetic material, or the genetic information, is, by 

 definition, transmitted from the mother cell to the daughter cell, 

 that is, multiplied. How does one molecule of nucleic acid produce 

 two identical molecules? How has nucleic acid solved the problem 

 of molecular reproduction? Desoxyribonucleic acid is a double 

 helix in M'hich adenine and thymine on the one hand and guanine 

 and cytosine on the other hand are united face to face by hydrogen 

 bonds. The double helix is thus composed of two complementary 

 strands. Watson and Crick in 1953 put forward the hypothesis 

 that each strand acts as a template for the organization of a comple- 

 mentary one. 



As the two strands of the duplex are complementary, the separa- 

 tion of the two strands cannot be described as a binary fission; it is, 

 in fact, an inequational cleavage, the separation of two different 

 parts. But as these parts are complementary, each one, when pro- 

 ducing its complement, reproduces the original molecule. The unit, 



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