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CELLS, TISSUES, AND ORGANISMS 



various cells by non-nuclear genetic determinants— the recognition that 

 all of the biological specificities of organisms ultimately reside in the 

 structures of specific macromolecules, and that these molecules are 

 synthesized in accordance with the general plan here outlined, has 

 resulted in an enormously simplified picture of the cellular economy. 



Figure 1. Highly diagrammatic picture of the components involved in cellular 

 biosynthesis. The genes, which are deoxyribonucleic acid (DNA), reside on 

 the chromosomes in the nucleus. Each gene, possessing the information that 

 spells out the structure of a single protein, transmits this structural message 

 to a molecule of RNA, which may be stored temporarily in a nucleolus but 

 eventually finds its way into cytoplasmic ribosomes attached to the endoplas- 

 mic reticulum that forms a connected series of labyrinths in the cytoplasm. 

 Small molecules of "transport RNA," each carrying a specific activated amino 

 acid, are lined up along particular large RNA molecules so as to form the 

 sequence of specific peptide bonds corresponding to a given protein struc- 

 ture. Many of the enzymes so synthesized are stored in the mitochondrial 

 particles, where they carry on the chemical work of the cell. Some of these 

 steps are not as yet fully substantiated, but the general outline seems well 

 established. 



