134 GENERAL BIOCHEMISTRY 



groups not directly involved in the reaction can affect the rate 

 or even prevent reaction. Whenever the side groups alter the reac- 

 tivity of a molecule, they will also alter the efficiency of the enzyme, 

 and the rate will be changed. 



Currently, investigators believe that only portions of an enzyme 

 molecule participate directly in the catalytic action. The nature and 

 spacing of the directly important groups determine the specificity of 

 the enzyme. When more is learned of the general requirements for 

 enzymatic activity, it may become possible to predict substrate function 

 after some knowledge of enzyme structure has been obtained. 



Biosynthesis 



The word biosynthesis refers to the method of synthesis employed by 

 cells. In the case of proteins and enzymes the mechanism of biosyn- 

 thesis is one of the greatest problems of biochemistry. Understanding 

 is necessary for that ultimate goal, the complete synthesis of a living 

 cell. Even now the development of concepts of enzyme synthesis has 

 led to theories of the origin and evolution of life. 



Much of the work on the biological formation of proteins has de- 

 pended on study of the synthesis of enzymes. This emphasis on the 

 latter arises from the biological label inherent in the catalytic activity 

 of enzymes, making them relatively easy to detect and measure. More- 

 over, the adaptive or inducible enzymes are natural subjects for study 

 because their formation can be initiated or at least accelerated by 

 suitably modifying the cellular environment. Yet in spite of this im- 

 portant starting point, only a few general ideas have been worked out. 

 The difficulties stem largely from the size and complexity of protein 

 molecules and from lack of knowledge of the nucleic acids. Since most 

 of our present information has been obtained in the last decade, the 

 next should provide great progress. 



Enzyme formation in particular and protein synthesis in general 

 obviously depend upon the presence of a supply of amino acids. 

 These components of the protein are then combined to form the 

 resulting specific macromolecule. There are several major problems 

 involved. Are the amino acids combined one after another, forming 

 a peptide that grows into protein? How is the synthesis controlled to 

 give a specific protein structure and not a mixture of all possible 

 structures? The energy content of a peptide or protein is higher than 

 that of a mixture of the individual amino acid components. Where 

 does this energy come from and how is it transferred dining the 

 formation of the peptide bonds? Are catalysts involved in the syn- 



