Heterocyclic aromatic amine bases

Nucleic acid A biopolymer containing three types of monomer units heterocyclic aromatic amine bases derived from purine and pyrimidine, the monosaccharides D-ribose or 2-deoxy-D-ribose, and phosphate. 

Controlled hydrolysis of nucleic acids yields three types of simpler building blocks heterocyclic aromatic amine bases, the monosaccharide D-ribose or 2-deoxy-D-ribose (Section 17.3), and phosphate ions. Figure 20.1 shows the five heterocyclic aromatic amine bases most common to nucleic acids. Uracil, cytosine, and thymine are referred to as pyrimidine bases after the name of the parent base adenine and guanine are referred to as purine bases. 

A nucleoside is a compound containing a pentose, either D-ribose or 2-deoxy-D-ribose bonded to a heterocyclic aromatic amine base by a /3-Atglycosidic bond (Section 17.4A). Table 20.1 gives the names of the nucleosides derived from the four most common heterocyclic aromatic amine bases. 

Names and one-letter abbreviations for the heterocyclic aromatic amine bases most common to DNA and RNA. Bases are numbered according to the patterns of pyrimidine and purine, the parent compounds. 

Uridine, a nucleoside. Atom numbers on the monosaccharide rings are primed to distinguish them from atom numbers on the heterocyclic aromatic amine bases. 

Deoxyribonucleic acids consist of a backbone of alternating units of deoxyribose and phosphate in which the 3 -hydroxyl of one deoxyribose unit is joined by a phosphodiester bond to the 5 -hydroxyl of another deoxyribose unit (Figure 20.5). This pentose—phosphodiester backbone is constant throughout an entire DNA molecule. A heterocyclic aromatic amine base—adenine, guanine, thymine, or cytosine—is bonded to each deoxyribose unit by a j8-Atglycosidic bond. The primary structure of a DNA molecule is the order of heterocyclic bases along the pentose-phosphodiester backbone. The sequence of bases is read from the 5 end to the 3 end. 

A nucleoside is a compound containing D-ribose or 2-deoxy-D-ribose bonded to a heterocyclic aromatic amine base by a 3-A/-glycosidic bond. 

A heterocyclic aromatic amine base is bonded to each deoxyribose unit by a /3-/V-glycosidic bond. 

Nucleosides are stable in water and in dilute base. In dilute acid, however, the glycosidic bond of a nucleoside undergoes hydrolysis to give a pentose and a heterocyclic aromatic amine base. Propose a mechanism for this acid-catalyzed hydrolysis. 

The clinical value of the nitrogen mustards lies in the fact that they undergo reaction with certain nucleophilic sites on the heterocyclic aromatic amine bases in DNA (see Chapter 28). For DNA, the most reactive nucleophilic site is N-7 of guanine. Next in reactivity is N-3 of adenine, followed by N-3 of cytosine. 

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See also in sourсe #XX -- [ , ]

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