CHEMICAL BONDS IN NUCLEIC ACIDS 



439 



-O 



OH OH 



Ad-CH- 



H H H 



OPO3H2 



Base— C2-— Cg— C5. 



P 

 Base — C2' — Cg.— C^, 



P 

 Base — C2- — C3. — Cg. 

 XXVI 



OPO3H2 



Base — C 2- — C3. — Cj, 



P' 

 Base-Co.— cC-a. 



Base — Cj.— Cg.— Cs- 

 XXIX 



O 



II 

 ch^-op: 



,0R 

 ^OH 



•0- 







Ad-CHCHO OHC-CH-CH,-OP: 



XXV 



Base — C 2'""G3'— Cj. 



Base-C2--C3.-C5._j^_, 



Base-C2.-C3.-Cj. 

 XXVII 



.OR 

 ^OH 



-0 



Base-CHCHO OHC-CH^CHj 

 P 



Base — Cj. C3. Cg, 



Jn-2 



Base — Co.- 



— CgT- 



XXVIII 



■'C., 



Base-C 



2- 



n-2 



"^3- /Cg. 

 P 



Base — C J. ~ Cg. — C5. 



P^ 

 Base— Cj. — Cg. "Cg. 



H2O3PO 

 XXVIa 



determinations have been made using phosphomonoesterase to remove a 

 terminal Cs'-phosphoryl group is not valid evidence of XXVI unless it can 

 be shown that the nucleic acid is completely intact; any partial degradation 

 of either type of polynucleotide would inevitably lead to structures of type 

 XXVI, on the basis of the accepted mechanism of hydrolytic breakdown. ^^^^ 

 A similar uncertainty exists in the case of the deoxyribonucleic acids. 



III. Structure of the Deoxyribonucleic Acids 



The deoxyribonucleic acids have generally been considered on titrimetric 

 data to be essentially high-molecular-weight polynucleotides which are 



"6a Since this review was written, Markham, Matthews, and Smith {Nature 173, 537, 

 1954) have shown that the nucleic acids of tobacco mosaic virus and potato virus 

 X belong in large proportion to the class represented by XXVIa; alkaline hydroly- 

 sis yields nucleoside-2'(and -3'),5'-diphosphates and nucleosides originating from 

 terminal residues. Other nucleic acids, e.g., from turnip yellow mosaic virus, ap- 

 pear to conform to structures of type XXVI, although, as indicated above, this 

 could be a reflection of their degraded state. 



