O INTRODUCTION 



Relation of biochemistry to biology 



Biologists have traditionally studied living organisms on the basis of 

 the cell, as the smallest intact living unit. The cell occupies much the 

 same relative position in biology as the molecule does in chemistry. 

 The smaller components of living cells have come under scrutiny, as the 

 biologist, equipped with ever more powerful microscopes, has probed 

 deeper and deeper into the mysteries of living matter. The main parts 

 of a typical cell are the cell wall, nucleus, and cytoplasm. The living 

 material making up the nucleus and cytoplasm is termed protoplasm; 

 it is a grayish, translucent, jelly-like material, which under the micro- 

 scope can be seen to consist of a meshwork filled with fluid. The nucleus 

 contains chromosomes, and these in turn, under very high magnification, 

 reveal structural irregularities which may have functional significance. 

 Thus the biologist studies and interprets life mostly in terms of its 

 smallest visible fragments. % 



From the chemical viewpoint, protoplasm is an aqueous, colloidal 

 solution containing protein as the chief solid ingredient, but with appre- 

 ciable amounts of fatty substances, nucleic acids, and other compounds 

 present. The metabolic reactions occurring in the cell take place in 

 this solution, and are studied and interpreted by the biochemist in terms 

 of molecules of the reacting substances. Most molecules are far too small 

 to be seen in any microscope, and their actual existence can only be sur- 

 mised from indirect evidence. However, the giant molecules of proteins 

 and nucleic acids are large enough so that they can actually be "seen," 

 that is, photographed, with the help of the electron microscope, an instru- 

 ment that makes possible 50,000-100,000 fold magnification. 



It seems most probable that the merging of biochemistry and biology 

 will continue in the future to an even greater extent, as the functional 

 activities of living things come more to be studied and explained in 

 chemical terms. However, it will not suffice to regard metabolism merely 

 as a group of chemical processes occurring at random in the same solu- 

 tion. Each living cell is a miniature "chemical factory" where food 

 molecules pass in an orderly fashion through a long series of interrelated 

 chemical reactions. A highly organized physical structure, with each 

 catalyst (enzyme) in a definite position in relation to the others, must 

 exist to accomplish this end. The study of such levels of organization 

 can probably be more properly classified as biology rather than as bio- 

 chemistry, although it must be obvious that the borderline is indefinite. 



Study of biochemistry 



The first task of the beginning student must be to learn something 

 of the materials of the cell in order to provide a basis for subsequent 



