Structures of Nucleic Acids and Nucleoproteins

The Genetic Significance of Nucleic Acids Transformation Is DNA-Mediated Structural Properties of DNA 

Most DNAs Exist as Double-Helix (Duplex) Structures 

Hydrogen Bonds and Stacking Forces Stabilize the Double Helix 

Duplex Structures Can Form Supercoils DNA Denaturation Involves Separation of Complementary Strands 

DNA Renaturation Involves Duplex Formation from Single Strands Chromosome Structure 

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In every living cell there are found nucleoproteins substances made up of proteins combined with natural polymers of another kind, the nucleic acids. Of all fields of chemistry, the study of the nucleic acids is perhaps the most exciting, for these compounds are the substance of heredity. Let us look very briefly at the structure of nucleic acids and, then, in the next section, see how this structure may be related to their literally vital role in heredity. 

Peacocke, a. R. The structure and physical chemistry of nucleic acids and nucleoproteins. 

The structures of sugars and polysaccharides are covered in the appropriate chapters within part 4 just prior to discussing their metabolism. Similarly, the structures of lipids are presented in the lipid metabolism chapters found in part 5. Nucleotide structures are addressed in chapter 23 before considering their metabolism. Finally, nucleic acid and nucleoprotein structures are examined in the first chapter (chapter 25) of part 7 prior to the discussion of the roles these molecules play in nucleic acid and protein metabolism in the six subsequent chapter. ... 

Hydrolysis of nucleoproteins separates the acids from the proteins. Further hydrolysis yields the components of nucleic acids, namely sugars, bases, and phosphoric acid. The nucleic acids differ from each other, depending upon the source, in chain lengths, sequences, and distributions of bases. As in the proteins, the primary structure of nucleic acids is determined by partial and sequential hydrolysis. 

Hooper, M. H. F. Wilkins, R. K. Barclay, and L. D. Hamilton (1955), Molecular structure of deoxyribose nucleic acid and nucleoprotein. Nature 175, 834-838. 

The protein portion of the nucleoproteins is basic in nature and being complex in structure may form several types of linkage, depending upon the type of nucleic acid. In gastric digestion or hydrolysis with weak acid, nucleoproteins yield protein and nuclein. The latter in pancreatic digestion or hydrolysis with weak alkali yields additional protein and nucleic add. See also Nucleic Acids. 

Although proteins and nucleic acids have well-separated functions in many instances, they also work intimately together in specific complexes containing both nucleic acid and protein. Some nucleoprotein complexes are very stable, some are transitory, and others have an intermediate stability. The protein component may provide a structural support for the nucleic acid, but in many cases, the two types of molecule both contribute directly to the function of the complex. Although cases of enzyme action by pure RNA molecules are rare, RNA molecules often act catalytically in nucleoprotein complexes. The chromosome was the first nucleoprotein complex to be discovered and is discussed first. Ribosomes have been studied intensively for many years and contain most of the RNA in the cell. More recently, nucleoprotein structures such as telomerase, spliceosomes, and signal-recognition particles have illustrated the versatility of nucleoprotein complexes. 

Many structures in the cell contain both nucleic acid and protein. Such nucleoprotein complexes are generally concerned with the storage and use of genetic information. 

In nature, the macromolecules of nucleic acids are found either free or as nucleoproteins with various topochemical distributions in the acellular (i.e., viral) and cellular (i.e., prokaryotes, eukaryotes) stmctures. The presence of these macromolecules in prokaryotes is not necessarily correlated with a defined morphologic structure. The localization in eukaryotes is generally in the cellular nucleus, but it is also present in the cellular cytoplasm, mitochondria, and plasmids. ... 

The unit structure of all living things is the cell. Suspended in the nucleus of cells are chromosomes, which consist largely of proteins and nucleic acids. The nucleic acids and proteins are intimately associated in complexes called nucleoproteins. Nucleic... 

Four processes are concerned in the isolation of a nucleic acid. First is the destruction of the tissue structure (stage 1). A nucleoprotein complex is then separated from other cellular constituents (stage 2). This complex is dissociated and the protein is removed (stage 3) and, finally, the nucleic acid is precipitated from the resulting solution (stage 4). Disintegration of... 

The genetic information of eukaryotic cells is propagated in the form of chromosomal DNA. Besides the nucleic acid component, chromosomes contain architectural proteins as stoichiometric components, which are involved in the protective compaction of the fragile DNA double strands. Together, the DNA and proteins form a nucleoprotein structure called chromatin. The fundamental repeating unit of chromatin is the nucleosome core particle. It consists of about 147 base pairs of DNA wrapped around a histone octamer of a (H3/H4)2 tetramer and two (H2A-H2B) heterodimers. One molecule of the linker histone HI (or H5) binds the linker DNA region between two nucleosome core particles (Bates and Thomas 1981). 

II A radically different type of nucleoprotein is that provided by the smaller RNA viruses of the elongated spiral type like tobacco mosaic, or of the polyhedral type such as tomato bushy stunt, tipula virus or poliomyelitis virus. The only one of these adequately studied has been tobacco mosaic virus, Franklin [19, 20], and here it appears that the protein and not the nucleic acid determines the structure. There is only one RNA chain and this is wound helically so that one protein is in contact with three successive nucleotides. 

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