38 The Chemistry of the Injured Cell 



Before we take a look at protein synthesis we must establish the 

 general setting for each of the varieties of protein. In so doing some 

 overlap into the chemistry of genetics is inevitable. We commence 

 with some remarks about the nucleoproteins. 



DNA is now known to be the chemical foundation of the chro- 

 mosomes, and in this way the key to protein behaviour is the cell. 

 Chromosomes are "undeniably strings of genes" (Lederberg, 1960) 

 and we must therefore look for the secret of gene behaviour in its 

 DNA which conceals the intricate chemical code that governs the 

 heredity of the cell. When a cell divides, its strands of DNA mole- 

 cules separate to form new chains which are allotted to each of the 

 daughter cells. By a replication process DNA provides the daughter 

 cells with "a complete set of instructions for their own complex 

 development and that of countless future generations of their 

 progeny" (Romberg, 1959) . Its molecule is not being constantly 

 broken down and resynthesised but apparently exists as two helical 

 chains each coiled around the same axis. Each chain consists of 

 phosphate groups joining the DNA residues; lying perpendicular 

 to the axis of the helices are the purine and pyrimidine groups 

 which link by H bonds. The basic protein chains of the nucleopro- 

 tein molecule probably wind round with the helix, being electro- 

 statically attracted by the phosphate residues in the polynucleotide 

 backbone. 



But DNA is something more than a blueprint. Genetical in- 

 vestigations suggest that the linear genetic information in DNA is 

 translated into linear information in the closely similar but smaller 

 RNA molecules that are available in the nucleus and that this RNA 

 directly controls protein synthesis in the cytoplasm. DNA behaves 

 as a kind of template for manufacturing the cell's structural pro- 

 teins and the associated enzymatic machinery that decides all of the 

 details and intimate behaviour of these proteins. Each strand of 

 DNA lays down along its length a series of small RNA nucleotides 

 as a set of working dies identically coded for beads of amino acids 

 attached to RNA in a manner which we must now discuss. 



Much uncertainty still exists about the way in which proteins 

 are built up in the cell. In all probability, amino acids, and not 

 peptides as was formerly assumed, are the prime units from which 



