Ribose 5-phosphate, composition

In theory, periodate oxidation could have given a clear-cut answer as to the composition of the isomeric mixture of deoxy ribose phosphates. The 4-phosphate (73), devoid of vicinal diol groups, should be resistant to periodate the 3-phosphate (74) should reduce one and only one molar equivalent of the oxidant and yield one molar equivalent of both formaldehyde and the phosphorylated dialdehyde (75), whereas the 5-phosphate (76) could be expected to reduce one molar equivalent of periodate relatively rapidly, followed by a slower overoxidation reaction owing to the oxidation of malonaldehyde, formed as a result of the glycol cleavage. 

DNA exhibits rather different properties from RNA in its susceptibility to acid and alkaline hydrolysis. The extreme acid lability of the iV-gly-cosy 1-purine linkages in DNA allows the quantitative liberation of free purines by very mild acid treatment, leaving a high molecular weight residue (called apurinic acid or thymic acid) complete in pyrimidine, deoxy-ribose, and phosphate composition 169), DNA, however, is quite stable to alkaline action since the absence of a hydroxyl group on carbon 2 of deoxy-ribose precludes the possibility of labilization through a cyclic 2, 3 -phos-phate intermediate. 

DNA and RNA. Quantitation of the (deoxy)ribose-phosphate backbone conformation and base composition observation of base pairing and base stacking (often different classes of bases can be monitored separately) H-D exchange in bases... 

All nncleic acids are polynucleotides, with each nucleotide being made np of a base, a sugar unit, and a phosphate. The composition of DNA differs from that of RNA in two major ways (see Figure 1). Whereas DNA contains the bases gnanine (G), cytosine (C), adenine (A), and thymine (T), RNA contains G, C, and A, but it contains uracil (U) in place of thymine. Both DNA and RNA contain a five-membered cyclic sngar (a pentose). RNA contains a ribose sngar. The sugar in DNA, however, is 2 -deoxyribose. 

The synthesis of RNA in extant biology, however, still relies upon the participation of proteins. The protein-fiTee de novo synthesis of RNA in a prebiotic reaction has yet to be demonstrated after several decades of effort (5). Many researchers have therefore concluded that RNA was not the first informational polymer of life. Rather, RNA was preceded by an RNA-Me polymer, or several generations of polymers, termed proto-RNAs, that were stracturally and functionally similar to RNA, but easier to assemble. Proto-RNA could have been comprised of different bases, sugars, and hnking molecules that were assembled through more thermodynamically and kinetically accessible pathways. Without the constraints of the current four RNA bases, ribose, and phosphate for the construction of an informational polymer, the possible composition of proto-RNAs seems limitless. However, tte existence of putative monomer units in the prebiotic chemical inventory for the assembly of proto-RNA would have been dictated by astro- and geochemical processes, paring down the set of molecules from which nature could select. 

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