CHAPTER 22 



THE CONTINUITY OF CELLS 



In Chapter 2 we learned the basic nature 

 of protoplasm and that it must duplicate 

 itself continuously. The large protein mole- 

 cules in protoplasm have the power to du- 

 plicate themselves through metabolism, 

 each kind producing others exactly like it- 

 self. Amino acids comins; to the cell from 

 without, together with those that are made 

 by the cell itself, are built into the protein 

 molecules of the cell in a very precise man- 

 ner, so that every molecule of a certain type 

 is exactly like every other one of that type. 

 Just how this is done is problematical, but 

 we are inclined to think it is through en- 

 zymes. As long as the proper amino acids 



continue to be present in the surrounding 

 environment, the huge protein molecules 

 continue to be formed. This is the begin- 

 ning of a duplicating mechanism that is 

 found among all living things and is the 

 basis for the continuity of life. 



DUPLICATION OF GENES 



We must rely on chemical means to un- 

 derstand duplication of protein molecules 

 but it is possible actually to see evidences 

 of duplication of the huge protein mole- 

 cules or aggregates of molecules which we 

 call genes. Genes are confined to chromO" 



551 



