Ribonucleic acid defined

Ribonucleases (RNases) may be defined as phosphodiesterases that attack the internucleotide bonds in ribonucleic acid (RNA) and its products but not those in deoxyribonucleic acid (DNA) or simple phos-phodiesters such as bis-p-nitrophenyl phosphate. 

As much of the terminology used in molecular biology may be unfamiliar to some readers, it is appropriate to define some of the vocabulary and this is given in an appendix to this chapter. There are two types of nucleic acids, the ribonucleic acids (RNA) and the deoxyribonucleic acids (DNA). Genetic information is carried in the linear sequence of nucleotides in DNA. Each molecule of DNA contains two complementary strands of deoxyribonucleotides which contain the purine bases, adenine and guanine and the pyrimidines, cytosine and thymine. RNA is single-stranded, being composed of a linear sequence of ribonucleotides the bases are the same as in DNA with the exception that thymine is replaced by the closely related base uracil. DNA replication occurs by the polymerisation of a new complementary strand on to each of the old strands. 

Biopolymers are either synthesized by template-dependent or template-independent enzymatic processes. For the synthesis of nucleic acids and proteins a template is required, whereas all other polymers are synthesized by template-independent processes. The templates for nucleic acids are desoxyribonucleic acids or ribonucleic acids depending on the type of nucleic acid synthesized. For proteins, the template is messenger ribonucleic acid (mRNA). This has different impacts on the structure and on the molecular weights (MWs) of the polymers. Although both nucleic acids and proteins are copolymers with each type consisting of 4 or 22 different constituents, respectively, the distribution of the constituents is absolutely defined by the matrix and is not random. Furthermore, each representative of the two polymers has a defined MW. Polymers synthesized in template-dependent processes are monodisperse. All this is different in polymers synthesized by template-independent processes first of all, these polymers are polydisperse secondly, if these polymers are copolymers, the distribution of the constituents is more or less fully random. 

All enzymes are proteins, with the exception of the recently discovered ribozymes. Ribozymes are special ribonucleic acids performing catalytic functions in the processing of RNA which will not be considered here. Proteins are polar macromolecules with molecular mass in the range 104-106. They are linear polymers, defined by the sequence of amino acids, which are linked by peptide bonds ... 

Nugent and Tyler (1959) were the first to evaluate the influence of defined dietary purines on uric acid metabolism after specific methods for uric acid estimations had become available. They added different doses of ribonucleic acid (RNA) to a low-purine diet and found an increase in serum and urinary uric acid with increasing amounts of RNA. This soon became a standard method in studies of uric acid metabolism. A dose of 4 g RNA has been used by various authors to produce mild hyperuricemia in normal subjects (Table 2). 

There are several distinct types of ribonucleic acid, which are defined in terms of molecular size, base composition and functional properties. They differ from DNA in... 

Reaction of Deoxyribonuclease. DNAase -acts on polymers of various lengths and forms a mixture of oligonucleotides with very little mononucleotide. Dinucleotides containing purines, pyrimidines, and both have been isolated from digests. The substrate specificity is obviously not so restricted as that of pancreatic RNAase, but has yet to be defined completely. The mechanism of action is also obscure. The linkage of phosphate to the 3 position is split by pancreatic DNAase the monoesters found in the products are all 5 -phosphates. From analogy with ribonucleic acid metabolism, it may be anticipated that DNAase with different specificities will be found, and that some will be found to split the 5 ester bonds. 

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