BIOSYNTHESIS OF PROTEINS 259 



towards the perimeter of the coil, and interchain stability must 

 depend, therefore, on side-chain interactions. The reactivity of 

 the molecule is further dependent both upon the sequence of 

 the amino acid residues along a single length of chain and upon 

 the relationships between the residues in adjacent chains. 



All these, ^vith other related factors, together determine 

 the complicated three-dimensional surface relief of the mole- 

 cule of any particular protein which is responsible for its 

 hormonal, enzymic, immunological or other biologically 

 important properties. 



The biosynthesis of proteins. 



It no^v remains for us to answer the question as to whether 

 such an extremely complicated and specific structure as the 

 molecule of a present-day protein with its definite amino 

 acid composition, its particular arrangement of amino acid 

 residues in a polypeptide chain and, finally, its precise 

 internal architecture, so thoroughly and well adapted to the 

 performance of definite biological functions, -^vhether this 

 structure cotild arise spontaneously, simply in the primaeval 

 aqueous solution of the hydrosphere. Many contemporary 

 authors answer this question in the affirmative, taking the 

 view that there first arose enzymes in this solution of organic 

 substances. These were self-reproducing proteins like viruses, 

 etc., and later combined together, giving rise to the primaeval 

 organisms. It is not, however, so easy to substantiate this 

 sort of general statement."® 



In the first place, how can one explain the origin of the 

 complicated sequences of amino acids w^hich are found in 

 insulin and other similar proteins? D. L. Talmud and S. E. 

 Bresler once suggested a hypothesis according to which the 

 polypeptide chain was an assemblage of different amino acids, 

 the proportions and sequence of ^shich Avere statistically 

 determined by their concentrations, but this hypothesis seems 

 to be an oversimplification. The free energies of the poly- 

 peptide bonds between the different amino acid residues 

 in a protein are not identical. There is also a correlation 

 between the heat effects of reactions and the energy of their 

 activation. Thus, according to A. G. Pasynskii,"' the incor- 

 poration of different amino acids into polypeptide chains 



