Structure of DNA and RNA

If you ve had a cup of coffee and your brain is functioning normally, you may have already guessed that /3-ribose is the sugar in the backbone of ribonucleic acids (RNA), while /3-2-deoxyribose forms the skeletal structure of deoxyribonucleic acid (DNA). In both types of polymers, these sugars are strung together by condensation reactions (remember those ) involving phosphoric 

FIGURE 9-40 Chemical structure of two sugars and phosphoric acid found in DNA and RNA. 

Because of the complementary nature of base pairing in the two strands of the DNA double helix, one chain essentially serves as 

DNA codes for the sequence of amino acids in the proteins that make up living organisms. How does it do this How does a message expressed in an alphabet that has 

RNA has a number of functions. For the purposes of protein synthesis, there are three main forms, messenger RNA, transfer RNA and ribosomal RNA. In addition, some RNAs are thought to be involved in catalytic processes, while in certain viruses RNA carries the genetic code. In the AIDs virus, for example, there are two (single) strands of RNA carrying the code for a new virus. Here we will confine our discussion to those RNA molecules that are involved in expressing genetic information. 

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In contrast, RNA occurs in multiple copies and various forms (Table 11.2). Cells contain up to eight times as much RNA as DNA. RNA has a number of important biological functions, and on this basis, RNA molecules are categorized into several major types messenger RNA, ribosomal RNA, and transfer RNA. Eukaryotic cells contain an additional type, small nuclear RNA (snRNA). With these basic definitions in mind, let s now briefly consider the chemical and structural nature of DNA and the various RNAs. Chapter 12 elaborates on methods to determine the primary structure of nucleic acids by sequencing methods and discusses the secondary and tertiary structures of DNA and RNA. Part rV, Information Transfer, includes a detailed treatment of the dynamic role of nucleic acids in the molecular biology of the cell. 

The secondary biological cycles stem from the crucial roles that phosphates and particularly organophosphates play in all life processes. Thus organophosphates are incorporated into the backbone structures of DNA and RNA which regulate the reproductive processes of cells, and they... 

The structures of DNA and RNA are similar in that each has a sugar-phosphate backbone with one organic base bound to each sugar. However, there are four distinct differences between RNA and DNA ... 

Figure 1.85 The chemical structure of DNA and RNA nucleotides. From H. R. Matthews, R. Freedland, and R. L. Miesfeld, Biochemistry A Short Course. Copyright 1997 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

The basic monomers of nucleic acids are nucleotides which are made up of heterocyclic nitrogen-containing compounds, purines and pyrimidines, linked to pentose sugars. There are two types of nucleic acids and these can be distinguished on the basis of the sugar moiety of the molecule, Ribonucleic acids (RNA) contain ribose, while deoxyribonucleic acid (DNA) contains deoxyribose. The bases cytosine (C) adenine (A) and guanine (G) are common in both RNA and DNA. However, RNA molecules contain a unique base, uracil (U), while the unique DNA base is thymidine (T). These differences in the base structure markedly affect the secondary structures of these polymers. The structures of DNA and RNA are outlined in Appendix 5.2. 

As we said earlier, nucleic acids are the architects and construction contractors for synthesizing proteins. There are two kinds of nucleic acids. DNA, or deoxyribonucleic acid, is the blueprint for synthesis of proteins. RNA, or ribonucleic acid, is the construction contractor. Messenger RNA reads the instructions for synthesis of a protein encoded on a strand of DNA and carries those instructions to the worksite, where transfer RNA brings the amino acids in for incorporation into the polypeptide chain. Now, let s take a closer look at the structures of DNA and RNA. 

Recognize the structures of DNA and RNA, and draw the structures of the common ribonucleotides and deoxyribonucleotides. 

Having discussed the primary structure of DNA and RNA, we now consider how the nucleotide sequence is reproduced or transcribed into another molecule. This information transfer takes place by an interesting hydrogen-bonding interaction between specific pairs of bases. 

One of the most important discoveries of modern science was the elucidation of the structures of DNA and RNA as the famous double helix by Watson and Crick in 1953. They realized that the basic structure of base-sugar-phosphate was ideal for a three-dimensional coil. The structure of a small part of DNA is shown opposite. 

Figure 9-2. Primary structure of DNA and RNA. Letters are the one-letter abbreviation of the nucleobases...

The Structure of DNA and RNA Double Helices is Determined by Watson-Crick Base-Pair Geometry... 

Chandrasekaran R, Arnott S (1989) The structures of DNA and RNA in oriented fibers. In Saenger W (ed) Nucleic acids, Landolt-BOrnstein New Series Group VII. Biophysics, vol. 1 b. Springer, Berlin, pp 31-170... 

Fig. 9.5 The molecular structures of DNA and RNA components the purine bases adenine and guanine, the pyrimidine bases cytosine, thymine and uracil and the structure of riboso-monophosphates.

The sequence or order of the nucleotides defines the primary structure of DNA and RNA. The nucleotides of the polymer are linked by phosphodiester bonds... 

In deoxyribonucleic acid (DNA) the carbohydrate is 2-deoxy-D-ribose, while in ribonucleic acid (RNA) the carbohydrate residue is ribose. Three types of RNA were recognized, and they can be messenger RNA (mRNA), transfer RNA (tRNA), or ribosomal RNA (rRNA), which is the most abundant in cells. Values between 10 and 10 Dalton have been reported for the molecular weight of DNA, and the molecular weight is about 10 for rRNA, 10 for mRNA, and lOMor rRNA. The simplified structures of DNA and RNA are the following ... 

In order to understand the mechanisms of pathogen disinfection by UV light, it is necessary first to be familiar with the structure of DNA and RNA, as they play key roles in two important aspects of reproduction of microorganisms protein synthesis and the replication of chromosomes. 

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