Chapter 3 

 NUCLEIC ACIDS AND GROWTH 



J. Bracket 



I. INTRODUCTION 



Cytochemical observations and biochemical experiments have, during the past 

 15 years, brought considerable evidence in favour of an important role of nucleic 

 acids in growth processes. The subject and the literature are so vast that only the 

 most important facts will be reviewed here, and reference will occasionally be 

 made to a number of recent comprehensive treatises where a host of additional 

 details can be found. 



After a brief introductory survey of nucleic acid chemistry and cellular locali- 

 zation, we will deal with the role of the two main types of nucleic acids: deoxyribo- 

 nucleic acid (DNA) and ribonucleic acid (RNA). While the former is important 

 in chromosome reduplication and genetic activity, RNA is, according to an in- 

 creasing number of biologists and biochemists, playing an essential role in protein 

 synthesis. The two types of nucleic acids are thus apparently involved in two 

 essential, but different, growth processes: increase in cell number and increase 

 in the most important constituents of the living matter, the proteins. 



This discussion of the role of DNA in mitosis and of RNA in protein synthesis 

 will be followed with a study of the part played by the nucleic acids in one of the 

 best known and most spectacular manifestations of growth: embryonic develop- 

 ment. 



Finally, the relationships existing between DNA and RNA metabolism, as 

 well as the importance of the cell nucleus in the growth of unicellular organisms, 

 will be discussed in the concludinar remarks. 



II. BRIEF SURVEY OF NUCLEIC-ACID CHEMISTRY AND CELLULAR 



LOCALIZATION 



{a) Chemical composition 



The considerable amount of knowledge which has accumulated on the chemis- 

 try, localization and biological role of the nucleic acids has been excellently 

 summarized in the recent treatise edited by Davidson and Chargaff, 1955. The 

 essential facts only will be briefly reviewed here. 



Two main types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic 

 acid (RNA) are found in every cell, whatever its function or origin. These two 



