I MATRICF-: J. niv'^SMAX 



materials for the synthesis of many other celhilar constituents. It is 

 probably the synthesis of deoxyribose or a derivative of it which is the 

 point of diversion from this non-sjiccific pool of precursors to the specific 

 sequence of reactions culniiiiatinfj; in the jjolynierization of the deoxy- 

 ribonucleoside triphosphates to form the DNA molecule. Since several 

 of the later chapters refer to specific reactions in this metabolic chain, 



CDP 



UDP- 



dHMP -^dHDP— -^ dHTP- 



dCMP 



dAMP 



dGMP 



-f 



dUMP 



dCDP dCTPmN 



dADP 



dGDP 



dTMP -dTDP 



dUDP 



dATP 



dGTP 



dTTP 



dUTP 



DNA ^ glucosyl DNA 



Fig. 1. Enzymatic reactions in E. coli leading to the sj'nthesis of DNA. , 



specific to cells infected with T-even phages. /WW, blocked in cells infected with 

 T-even phages. 



tlie current concepts of the pathways of enzymatic synthesis of deoxy- 

 ribonucleotides and their phosphorylated derivatives will be discussed 

 briefiy with the intention of providing an immediate reference for the 

 ensuing chapters. Figure 1 shows several of the reactions suggested as 

 intermediate steps leading to the synthesis of DNA. 



In the cell-free system, the replication of DNA imi)lics the net 

 synthesis of exact replicas of the "primer" molecules. For this reason, 

 only those systems sufficiently iiurificd to dcmon.-^tiatc both net .synthesis 



nuclease; AMP, ADP, ATP: adenosine monophosphate, adenosine diphosphate, 

 adenosine triphosphate; CMP, CDP, CTP: cytidine monophosphate, etc.; GMP, 

 GDP, GTP: guanosine monophosphate, etc.; HMP, HDP, HTP: hydroxj-methyl- 

 cytidine monophosi)hate, etc.; IMP, IDP, ITP: inosine monophosphate, etc.; TMP, 

 TDP, TTP: thymidine monophosphate, etc.; UMP, UDP, UTP: uridine monophos- 

 phate, etc.; dAMP, dADP, d.\TP: deoxyadcnosinc monophosphate, etc.; DPN, 

 DPXH: diphosphoi)yridino and its reduced form; TPN, TPNH: triphosphopyridine 

 and its reduced form; F.\D, FADH;: flavin adenine dinucleotide and its reduced 

 form; THFA: tetrahydrofolic acid; Pi, PPi : inorganic ortlu)i)hos])hate and pyro- 

 phosphate ; tris: tris(hj'dro.\ymethyl)aminomethane. 



