INTRODUCTION 



Objectives and methods of biochemistry 



The ultimate objectives of the science of biochemistry are a complete 

 knowledge of the structure and properties of all chemical compounds 

 present in living things and a complete understanding of the chemical 

 reactions they undergo both in health and disease. Usually, knowledge 

 of materials must first be obtained before much can be learned about 

 their function. At the present time the chief types of organic substance 

 in most biological materials are fairly well known. These major com- 

 ponents are the carbohydrai,es, fats and proteins. However, it has be- 

 come increasingly clear during the last few decades that many compounds, 

 e.g., vitamins and hormones, normally present in living cells in only 

 very small amounts often play important physiological roles. An im- 

 pressive number of these compounds is now known, but many more cer- 

 tainly remain to be studied. The development of our knowledge of 

 metabolism is even more recent and incomplete. Some of the processes 

 involving food utilization and energy production are emerging into focus, 

 but as yet only the barest beginning has been made in finding out what 

 chemical reactions occur during the normal functioning of living things. 



Biochemical research is being intensively pursued in hundreds of labora- 

 tories throughout the world. The methods of study are drawn mainly 

 from the older sciences such as chemistry, physics, mathematics, biology, 

 physiology, etc., of which biochemistry is an outgrowth and descendant. 



Isolation Methods. Efforts to ascertain the chemical nature of bio- 

 logical materials ordinarily start with an extraction or purification process 

 by which one constituent is isolated, i.e., separated in pure form from 

 all the others. The isolation of a pure biological substance is often a 

 difficult feat because most biological materials are complex mixtures 

 containing hundreds of different individual chemical substances, many 

 of which frequently are closely similar in composition or properties and, 

 therefore, difficult to separate. In addition, the particular substance 

 sought may be present in very low concentrations, perhaps only one 

 part in many million parts of the source material. For example, Doisy 

 and co-workers extracted and processed the equivalent of four tons of 

 sow ovaries to obtain about 10 mg. of the sex hormone, estradiol (p. 292). 

 This small yield represented about half of the hormone originally present, 

 since its normal concentration in the ovary of the sow is only one part 

 in 150,000,000! This isolation of estradiol represents an achievement 

 on a par with the famous work of the Curies in obtaining radium from 

 pitchblende and illustrates some of the difficulties which confront the 

 biochemical investigator studying the composition of living things. 



There are many kinds of procedure used in isolating biochemical sub- 

 stances, and only a brief indication of their nature can be attempted 



