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MAMMALIAN CELL GROWTH 

 IN TISSUE CULTURE* 



Theodore T, Puck 



UNIVERSITY OF COLOR-\DO 



Within the last several decades, the intimate structures and functions 

 of the living cell have achieved a clarity of definition which would 

 hardly have been conceivable 50 years ago. The nuclear, genetic de- 

 terminants have been resolved into molecules of DNA, each of which 

 has its informational content carefully stored in the specific linear 

 sequence of its one or two thousand base pairs. This information is 

 transmitted to the cytoplasm by large RNA molecules, which are stored 

 in the several hundreds of thousands of ribosomes that are strung on a 

 succession of parallel layers extending from the cell membranous wall 

 throughout the cytoplasm. Each such RNA molecule presumably brings 

 about the synthesis of a specific protein, whose component amino acids 

 are transported to the final assembly site on the large RNA template by 

 small, carrier RNA molecules, each of which specifically binds a par- 

 ticular amino acid, provided it has been properly activated. 



Delicately balanced feedback mechanisms, operating either to pre- 

 vent this gene-controlled biosynthesis of any given protein, or to inhibit 

 its action biologically, serve to regulate the cell's metabolic activities, in 

 accordance with the needs imposed by its environment. Many of the 

 proteins that constitute the enzymes are stored in the mitochondrial 

 particles, much larger and fewer in number than the ribosomes, and 

 these carry on the major chemical work of forming and liberating en- 

 ergy from the small molecules whose flow maintains metabolism ( Fig- 

 ure 1 ) . While many obscurities still remain— such as the role played in 



^Contribution No. 116 from the Department of Biophysics, Florence R. 

 Sabin Laboratories, Universittj of Colorado Medical Center, Denver. This work 

 was supported by a firant from The National Foundation. 



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