Ribonucleic acids structures

RM Reference Material RNA ribonucleic acid (structural element of the cytoplasm and cell nucleus), consisting of D-ribose sugar, the nitrogenous bases adenine, guanine, cytosine and uracil. There are three different types transfer RNA, messenger RNA and ribosomal RNA RNAA radiochemical neutron activation analysis (post irradiation radiochemical separation)... 

Figure 29-1. Conventions for writing ribonucleic acid structures for a short RNA chain with (from left to right) adenosine, uridine, guanosine, and cytidine nucleosides.

Reactions of Ribonuclease. The degradation of ribonucleic acid by RNAase was found to result in the accumulation of a mixture of pyrimidine mononucleotides and a so-called core. The core is not an individual structure it is a mixture of oligonucleotides in which the bases are predominantly purines. These compounds indicate the random nature of the ribonucleic acid structure. Ribonuclease hydrolyzes esters of doubly esterified phosphate in which one of the substituents is the hydroxyl group in position 3 of a pyrimidine nucleotide the other substituent, which in ribonucleic acid is a 5 hydroxyl group, is removed. Since groups substituted on phosphates esterified with 3 positions of purine... 

Ribonucleic acid is thought to possess a highly branched structure. Cleavage about a branch point in the manner illustrated in (VIII) would give the pyrimidine nucleoside diphosphates discussed above. Ribonucleic acid also contains a number of phospho-monoester end groups which are susceptible to acid prostatic phosphatase and certain other monoesterases. A great deal has been learned of ribonucleic acid structure... 

D-ribose, CjHioOj. M.p. 87 0. The sugar of ribonucleic acid it is therefore present in all plant and animal cells. It has the furanose structure shown. 

Nucleic acids are acidic substances present m the nuclei of cells and were known long before anyone suspected they were the primary substances involved m the storage transmission and processing of genetic information There are two kinds of nucleic acids ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) Both are complicated biopolymers based on three structural units a carbohydrate a phosphate ester linkage between carbohydrates and a heterocyclic aromatic compound The heterocyclic aro matic compounds are referred to as purine and pyrimidine bases We 11 begin with them and follow the structural thread... 

Cytosine was isolated from hydrolysis of calf thymus in 1894 and by 1903 its structure was known and it had been synthesized from 2-ethylthiopyrimidin-4(3H)-one. The acid hydrolysis of ribonucleic acid gives nucleotides, among which are two cytidylic acids, 2 -and 3 -phosphates of cytidine further hydrolysis gives cytidine itself, i.e. the 1-/3-D-ribofuranoside of cytosine, and thence cytosine. The deoxyribonucleic acids likewise yield deoxyribonucleotides, including cytosine deoxyribose-5 -phosphate, from which the phosphate may be removed to give cytosine deoxyriboside and thence cytosine. 

Adding nucleotides to the 3 -oxygen of an existing structure is called elongation and leads ultimately to a polynucleotide. The most important polynucleotides ar e ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). As we shall see in later sections, the polynucleotide chains of DNA and some RNAs are quite long and contain hundreds of thousands of bases. 

Ribose, an essential part of ribonucleic acid (RNA), has the following structure ... 

The discovery of the base-paired, double-helical structure of deoxyribonucleic acid (DNA) provides the theoretic framework for determining how the information coded into DNA sequences is replicated and how these sequences direct the synthesis of ribonucleic acid (RNA) and proteins. Already clinical medicine has taken advantage of many of these discoveries, and the future promises much more. For example, the biochemistry of the nucleic acids is central to an understanding of virus-induced diseases, the immune re-sponse, the mechanism of action of drugs and antibiotics, and the spectrum of inherited diseases. 

Ribonucleic acid (RNA) Molecules including messenger RNA, transfer RNA, ribosomal RNA, or small RNA. RNA serves as a template for protein synthesis and other biochemical processes of the cell. The structure of RNA is similar to that of DNA except for the base thymidine being replaced by uracil. 

RNA RNA (ribonucleic acid) is an information encoded strand of nucleotides, similar to DNA, but with a slightly different chemical structure. In RNA, the letter U (uracil) is substituted for T in the genetic code. RNA delivers DNA s genetic message to the cytoplasm of a cell where proteins are made. 

A detailed discussion of the modes of occurrence and biological importance of the polynucleotides is outside the scope of this article. However, in examining the structures of polynucleotides, it is necessary to take into consideration the origins of the materials studied. The pioneer researches of Caspersson114 indicated that deoxyribonucleic acids are present exclusively in the nucleus, whereas ribonucleic acids are found chiefly in the cytoplasm and only to a small extent in the nucleus. This general outline of the distribution of nucleic acids within the cell has been confirmed and extended by more recent work,116 and it has been possible to isolate both types of nucleic acid from different cellular fractions of the same tissue.116... 

Before considering newer conceptions concerning the structures and properties of ribonucleic acids, it will be necessary to summarize the previous position. 

The position was somewhat clarified by the isolation of 2- and 3-O-phos-phonucleosides from ribonucleic acid hydrolyzates in 92 to 100% yields,134 and also by the demonstration that 5-O-phosphonucleosides are also present in enzymic digests.49, 197 Yet this information gave no indication of the nature of the alkali-labile linkages. Thus, while the majority of the experimental evidence pointed to the phosphoryl residues as being doubly esterified with adjacent nucleosides, two facts remained apparently inexplicable on the basis of this type of structure. First, ready fission by alkalis, and secondly, the absence of 5-phosphates from alkaline hydrolyzates and their presence in enzymic digests. Both these facts have been explained by Brown and Todd in the following way.92... 

Such a structure cannot be constructed for a ribopolynucleotide, since the extra oxygen atom would result in too close a van der Waals contact. However, x-ray photographs of ribonucleic acids from various sources are found to be identical, which suggests that, irrespective of differences in composition, there is an underlying configuration which is common to all... 

Nitrogenous base plus sugar moiety are called nucleosides. Ribonucleic acids (RNA) resemble DNA in that nucleoside monophosphates are joined through phosphodiester bonds. RNAs differ in that the sugars are p-D-ribose units and the pyrimidine uracil is found in place of thymine. Molecular structures and nomenclature for nitrogenous bases, nucleosides, and nucleotides are delineated in Table 2.2. 

---