Nucleotides in DNA and RNA

Next to nucleotides in DNA and RNA, related compounds may be present in living systems. For instance, adenosine mono-, di-, and triphosphate (AMP, ADP, and ATP) play an important role in energy management of many enzymatic reactions. 

Structure of the nucleotide in DNA and RNA. The base adenine is used as an example. See Table 27-1 for a complete nomenclature of nucleosides and nucleotides. 

Nucleotides in DNA and RNA. Nucleotides are the monomeric units of the nucleic acids, DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Each nucleotide consists of a heterocyclic nitrogenous base, a sugar, and phosphate DNA contains the purine bases adenine (A) and guanine (G) and the pyrimidine bases cytosine (C) and thymine (T). RNA contains A, G, and C, but it has uracil (U) instead of thymine. In DNA, the sugar is deoxyribose, whereas in RNA it is ribose. 

Table 1. Designations of the Nucleosides and Nucleotides in DNA and RNA ph = phosphate, d = deoxy-(d- is often omitted when it is obvious that a deoxy compound is being referred to)...

The name of a nucleoside that contains a purine ends with osine, whereas a nucleoside that contains a pyrimidine ends with idine. The names of the nucleosides of DNA add deoxy to the beginning of their names. The corresponding nucleotides in RNA and DNA are named by adding -5 -monophosphate. Although the letters A, G, C, U, and T represent the bases, they are often used in the abbreviations of the respective nucleosides and nucleotides. The names and abbreviations of the bases, nucleosides, and nucleotides in DNA and RNA are listed in Table 17.2. 

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 ... 

Table 2.2 Nitrogenous Bases, Nucleosides, Nucleotides, and Sugars Found in DNA and RNA...

Figure 4.15 k summary of the fate of nucleosides that are produced from RNA digestion in the lumen of the intestine. The nucleosides produced from RNA in the lumen are absorbed by the enterocytes and then transported from the intestine into the blood from where they are taken up by cells (especially proliferating cells, e.g. in the bone marrow) to form nucleotides for DNA and RNA synthesis. (See Chapter 10) NTP is nucleoside triphosphate. 

Tumour cells also require glutamine as a fuel for energy generation and as a precursor for the synthesis of purine and pyrimidine nucleotides for DNA and RNA synthesis. The roles and importance of glutamine in tumour cells and possible competition between the cells for glutamine are discussed in Chapter 21. The pathway for the metabolism of glutamine is similar to that in the immune cells. 

A set of coding rules are in action as in the translation process. First, a set of three adjacent nucleotides compose the code for each amino acid. A single amino acid can have several triplet codes or codons. Since there are four different nucleotides (or four different bases) in DNA and RNA, there exist 4 = 64 trinucleotide combinations. For instance, using U as a symbol for uracil, which is present in RNA, the triplet or code or codon UUU is specific for phenylalanine. 

Both the process of replication and the copying of the genetic code into molecules of RNA depend on base pairing. The nitrogen bases in the nucleotides of DNA and RNA pair in a specific way. In... 

Figure 1.28 (a) The general structure of a nucleotide, (b) A schematic representation of a section of a nucleic acid chain, (c) The bases commonly found in DNA and RNA. These bases are indicated by the appropriate letter in the structures of Nucleic acids. Thymine is not found in RNA it is replaced by uracil, which is similar in shape and structure, (d) Examples of nucleosides found in DNA and RNA... 

Todd s research provided the knowledge of how the nucleotides are linked in DNA and RNA and thus it belongs to the basis of James D. Watson s (b.1928) and Francis H. Crick s (b.1916) work on the structure of DNA, the double helix. In addition, his work on coenzymes opened new vistas for the understanding and manipulation of many biochemical processes and thus contributed fundamentally to concepts that soon would become of use in medicinal chemistry. 

One of the pioneers of structured models in animal cell culture used a single-cell model (Batt and Kompala, 1989). Based on hybridoma metabolism (.Figure 8.6), the model was based on the formulation of four compartments amino acids (including the TCA precursors), the nucleotides (including DNA and RNA), the proteins, and lipids. The excreted byproducts (lactate and ammonia) and the excreted product (mAb) were also considered. However, although flexible for simulation of different... 

Carbamoyl phosphate is an activated ammonia group that is important in the biosyntheses of the amino acid arginine and of the pyrimidine nucleotides found in DNA and RNA. 

Purine and pyrimidine nucleotides fill a variety of metabolic roles. They are the energy currency of the cell. In some cases, they are signaling molecules, acting like hormones directly or as transducers of the information. They provide the monomers for genetic information in DNA and RNA. 

The purine ring system is undoubtedly among the most ubiquitous of all the heterocyclic compounds. This arises not only from the universal occurrence of adenine and guanine in DNA and RNA and of additional modified derivatives in the various tRNAs but also from the subsidiary uses of the ring system in very many biochemical systems Indeed across the whole spectrum of biochemical reactions in living systems there is hardly a reaction sequence which does not involve in some way a purine derivative such as the adenosine or guanosine mono-, di- and tri-phosphates, associated cyclic phosphates and nucleotide coenzymes. 

Nucleotides join together in DNA and RNA by forming a phosphate ester bond between the 5 -phosphate group on one nucleotide and the 3 -hydroxyl group on the sugar of another nucleotide (Figure 28.5). One end of the nucleic acid polymer has a free hydroxyl at C3 (the 3 end), and the other end has a phosphate at C5 (the 5 end). 

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