Ribonucleic acid sugar component

Nucleic Acids. Phosphoms is an essential component of nucleic acids, polymers consisting of chains of nucleosides, a sugar plus a nitrogenous base, and joined by phosphate groups (43,44). In ribonucleic acid (RNA), the sugar is D-ribose in deoxyribonucleic acids (DNA), the sugar is 2-deoxy-D-ribose. 

As is well-known, nucleic acids consist of a polymeric chain of monotonously reiterating molecules of phosphoric acid and a sugar. In ribonucleic acid, the sugar component is represented by n-ribose, in deoxyribonucleic acid by D-2-deoxyribose. To this chain pyrimidine and purine derivatives are bound at the sugar moieties, these derivatives being conventionally, even if inaccurately, termed as pyrimidine and purine bases. The bases in question are uracil (in ribonucleic acids) or thymine (in deoxyribonucleic acids), cytosine, adenine, guanine, in some cases 5-methylcytosine and 5-hydroxymethylcyto-sine. In addition to these, a number of the so-called odd bases occurring in small amounts in some ribonucleic acid fractions have been isolated. 

The nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), which carry embedded in their complex molecules the genetic information that characterizes every organism, are found in virtually all living cells. Their molecules are very large and complex biopolymers made up basically of monomeric units known as nucleotides. Thus DNA and RNA are said to be polynucleotides. The nucleotides are made up of three bonded (linked) components a sugar, a nitrogenous base, and one or more phosphate groups ... 

The nucleic acids play a central role in the storage and expression of genetic information (see p. 236). They are divided into two major classes deoxyribonucleic acid (DNA) functions solely in information storage, while ribonucleic acids (RNAs) are involved in most steps of gene expression and protein biosynthesis. All nucleic acids are made up from nucleotide components, which in turn consist of a base, a sugar, and a phosphate residue. DNA and RNA differ from one another in the type of the sugar and in one of the bases that they contain. 

The term nucleoside was originally proposed by Levene and Jacobs in 1909 for the carbohydrate derivatives of purines (and, later, of pyrimidines) isolated from the alkaline hydrolyzates of yeast nucleic acid. The phosphate esters of nucleosides are the nucleotides, which, in polymerized forms, constitute the nucleic acids of all cells.2 The sugar moieties of nucleosides derived from the nucleic acids have been shown, thus far, to be either D-ribose or 2-deoxy-D-eri/fAro-pentose ( 2-deoxy-D-ribose ). The ribo-nucleosides are constituents of ribonucleic acids, which occur mainly in the cell cytoplasm whereas 2-deoxyribo -nucleosides are components of deoxypentonucleic acids, which are localized in the cell nucleus.3 The nucleic acids are not limited (in occurrence) to cellular components. They have also been found to be important constituents of plant and animal viruses. 

All our descriptions of ribonucleosides, ribonucleotides, and ribonucleic acid also apply to the components of DNA. The principal difference between RNA and DNA is the presence of D-2-deoxyribose as the sugar in DNA instead of the D-ribose found in RNA. The prefix deoxy- means that an oxygen atom is missing, and the number 2 means it is missing from C2. 

These purines and pyrimidines join to the sugar-phosphate backbones of nucleic acids through repeating /3-linked AT-glycosidic bonds involving the N9 position of purines and the N1 position of pyrimidines. There are two classes of nucleic acids ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). DNA and RNA differ in one of their nitrogenous base components (uracil in RNA, thymine in DNA) and in their sugar (ribose) moiety, as indicated in Fig. V-2. 

In the presence of formaldehyde (0.5 mol equiv.), sugar phosphates were formed in up to 45% yield, with pentose-2,4-diphosphates dominating over hexose triphosphates by a ratio of 3 1 (Scheme 13.2, Route B). The major component was found to be D,L-ribose-2,4-diphosphate with the ratios of ribose-, arabinose-, lyxose-, and xylose-2,4-diphosphates being 52 14 23 11, respectively. The aldomerization of 2 in the presence of H2CO is a variant of the formose reaction. It avoids the formation of complex product mixtures as a consequence of the fact that aldoses, which are phosphorylated at the C(2) position, cannot undergo aldose-ketose tautomerization. The preference for ribose-2,4-diphosphate 5 and allose-2,4,6-triphosphate formation might be relevant to a discussion of the origin of ribonucleic acids. 

The carbohydrate component of ribonucleic acid and, therefore, of the corresponding purine nucleosides was identified as a pentose by Hammar-sten and, later, as D-ribose by degradation and then by synthesis. Because of the instability of 2-deoxy-D-erythro-peutose ( 2-deoxy-D-ribose ), its isolation from deoxyribonucleic acid was much more difficult. Levene and coworkers finally obtained the crystalline sugar from deoxyguanosine by brief treatment with dilute mineral acid. They established its identity by comparison with synthetic 2-deoxy-D-threo-pentose and 2-deoxy-L-er /[Pg.303]

Nicotinamide adenine dinucleotide (NAD) is the coenzyme form of the vitamin niacin. Most biochemical reactions require protein catalysts (enzymes). Some enzymes, lysozyme or trypsin, for example, catalyze reactions by themselves, but many require helper substances such as coenzymes, metal ions, and ribonucleic acid (RNA). Niacin is a component of two coenzymes NAD, and nicotinamide adenine dinucleotide phosphate (N/kDP). NAD (the oxidized form of the NAD coenzyme) is important in catabolism and in the production of metabolic energy. NADP (the oxidized form of NADP) is important in the biosynthesis of fats and sugars. 

Nucleic acids are vital molecules which carry the genetic code and are responsible for its expression by protein synthesis. The two types of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). The components of these acids can be obtained by hydrolysis. Partial hydrolysis of a nucleic acid produces nucleotides, which consist of a base, a sugar and a phosphate group. Nucleotides are monomers for nucleic acid polymers, as illustrated in Figure 6.6b. 

Nucleic acids are classified into two categories ribonucleic acid (RNA), found mainly in the cytoplasm of living cells, and deoxyribonucleic acid (DNA), found primarily in the nuclei of cells. Both DNA and RNA are polymers, consisting of long, linear molecules. The repeating structural units, or monomers, of the nucleic acids are called nucleotides. Nucleotides, however, are composed of three simpler components a heterocyclic base, a sugar, and a phosphate (see > Figure 11.2). These components will be discussed individually. 

The sugar component of RNA is o-ribose, as the name ribonucleic acid implies. In deoxyribonucleic acid (DNA), the sugar is o-deoxyribose. Both sugars occur in the 3-configuration. 

Nucleic acids are classified into two categories ribonucleic acids (RNA) and deoxyribonucleic adds (DNA). Both types are polymers made up of monomers called nucleotides. All nucleotides are composed of a pyrimidine or purine base, a sugar, and phosphate. The sugar component of RNA is ri-bose, and that of DNA is deoxyribose. The bases adenine, guanine, and cytosine are found in aU nucleic acids. Uracil is found only in RNA, and thymine only in DNA. 

Of the eight aldopentoses D-ribose is the most important from the biochemical point of view. It is a component of various coenzymes as well as the ribonucleic acids. Closely related to it is D-2-deoxyribose which differs only in the absence of an O atom from the second carbon of the sugar chain. 

There are two closely related types of nucleic acids deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Both are polymers of repeating monomer units known as nucleotides. A DNA molecule may contain several million nucleotides smaller RNA molecules may contain up to several thousand. Each nucleotide has three components a base, a five-carbon sugar, and a phosphate group (see Figure 18.16). 

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