156 BIG MOLECULES 



There are extensions and modifications of the cog and cam theories, and 

 even other theories of the physical arrangements on DNA and RNA. The 

 experimental problem is not made simpler by the fact that there are 

 20 x 19 x 18- •• = 2.3 x 10 17 different ways in which 20 different amino 

 acids can be hooked together! Some "selection rules" must therefore follow 

 from a code, for, as Gamov says "if one could spend only one second to 

 check each assignment, one would have to work continuously for about five 

 billion years, which is [estimated to be] the present age of our Universe! " 



Other experimental work has brightened the picture still further. For in- 

 stance, only with a specific enzyme does an amino acid form a complex with 

 ATP; polymerization and depolymerization occur in DNA and RNA; com- 

 plex formation occurs between the low-molecular-weight, soluble (or "trans- 

 fer") RNA and the DNA molecule; the helical shape of DNA is well estab- 

 lished in moist air; and chemical analyses have been made of certain mole- 

 cules. All these are experimental facts. There are many, many variables, 

 better knowledge of which will clarify the theory. 



MUTATIONS AND MOLECULAR DISEASES 



The idea of "sick people from bad molecules" is not really new, although 

 it certainly has been experimentally demonstrated in very convincing 

 fashion and exploited heavily since 1948. While Washington was busy on 

 the Delaware, Scheele in Germany showed that there is a good and bad form 

 of adrenalin. By 1913, F. G. Hopkins was able to state with some bio- 

 chemical authority: "Metabolic processes on which life depends consist in 

 toto of a vast number of well-organized and interlocking enzymic reactions, 

 interference with any one of which can product deleterious effects . . . ." The 

 quotation from Pauling, with which this Chapter began, concerning the 

 need for better understanding of macromolecules and catalysts, is the mod- 

 ern approach to this question. 



We have seen that, because of structural and/or compositional changes 

 in macromolecules, the following results may accrue: 



( 1 ) Change in rate of chemical processes 



(2) Change in rate of physical processes 



(3) Introduction of new side reactions 



A simple example of (3), introduced before recorded history and persisting 

 faithfully to our day, is offered in the different blood types in man: O, A, B, 

 AB. These differ from each other only in that the colloidal-stabilizing 

 mechanism of the macromolecules of the blood plasma is different: for if two 

 of the types are mixed, they agglutinate or gel; the mixture becomes thick 

 and refuses to flow. The physical nature of this subtle difference which 

 makes them incompatible still escapes us. The production, by each indi- 



