DNA and RNA Building Blocks

Inhibition of nucleobase synthesis (2). Tetrahydrofolic acid (THF) is required for the synthesis of both purine bases and thymidine. Formation of THF from folic acid involves dihydrofolate reductase (p. 272). The folate analogues aminopterin and methotrexate (ame-thopterin) inhibit enzyme activity as false substrates. As cellular stores of THF are depleted, synthesis of DNA and RNA building blocks ceases. The effect of these antimetabolites can be reversed Ltillmann, Color Atlas of Pharmacology 2000 Thieme All rights reserved. Usage subject to terms and conditions of iicense. 

Nucleic acids Biopolymers whose monomers are nucleotides. They are one of the building blocks of DNA and RNA. 

Nucleotides serve as the building blocks for synthesis of the nucleic acids DNA and RNA. 

Nucleosides are the building blocks of DNA and RNA and contain a carbohydrate unit together with a base. A number of derivatives have been prepared as pharmaceutical agents, perhaps the best known being AZT (azidothymidine, or zidovudine) (12). Some of these compounds may be accessed from ribose.35 In many cases, a nucleoside is used as the starting material for modification a number of routes to 12 use this approach.36 38... 

Other successes were reported in the early years of research on the origin of life. Perhaps the most notable achievement was by the laboratory of Juan Oro. They showed that the simple chemical hydrogen cyanide would react with itself to yield a number of products including adenine, which is a component of one of the building blocks of nucleic acids. The result cracked open DNA and RNA as targets for chemical investigation... 

Sugars are the building blocks of carbohydrates. They used to be thought of as essential but rather dull molecules whose only functions were the admittedly useful provision of energy and cell wall construction. We have already noted that ribose plays an intimate role in DNA and RNA structure and function. More recently, biochemists have realized that carbohydrates are much more exciting. They are often found in intimate association with proteins and are involved in recognition of one protein by another and in adhesion processes. 

Applying the same analysis to pyrimidines (3 and 6) leads to pyrimidones, examples of which are the pyrimidine bases in DNA and RNA. Thus deoxycytidine 46 and deoxythymidine 47 are two of the four 2 -deoxyribonucleosides that are the building blocks of DNA and uridine 48 is one of the four nucleoside building blocks of RNA. As for pyridones, the contribution of dipolar resonance hybrids to pyrimidones and other systems with exocyclic conjugation often helps to understand their properties, including their aromatic character. 

A major role for many sequences of DNA is to encode the sequences of proteins, the workhorses within cells, participating in essentially all processes. Some proteins are key structural components, whereas others are specific catalysts (termed enzymes) that promote chemical reactions. Like DNA and RNA, proteins are linear polymers. However, proteins are more complicated in that they are formed from a selection of 20 building blocks, called amino acids, rather than 4. 

Figure 14.1. The biochemistry of nucleic acid. DNA and RNA are linear polymers in which each building block is a nucleotide. Nucleotides make up a ribose-phosphate scaffold, to which a base is joined. Four bases are used in both DNA and RNA adenine, cytosine, guanine, and thymine (used in DNA, modified from the chemically similar uracil used in RNA).

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