Polynucleic acid

For the purposes of the following discussion small molecules are considered to have fewer than 200 nonhydrogen atoms. Macromolecules, primarily proteins, polynucleic acids, and vimses, can have many thousands of atoms. 

The procedures for solving and refining macromolecular stmctures are similar to those for smaH molecules. The class of macromolecular stmctures solved consists mostly of proteins, some polynucleic acids, and some viral stmctures. These stmctures usuaHy contain thousands of atoms. 

Ribonuclease II [EC 3.1.13.1], also called exoribo-nuclease II, catalyzes the exonucleolytic cleavage of the polynucleic acid, preferring single-stranded RNA, in the 3 - to 5 -direction to yield 5 -phosphomononucleotides. The enzyme processes 3 -terminal extra-nucleotides of monomeric tRNA precursors, following the action of ribonuclease P. Similar enzymes include RNase Q, RNase BN, RNase PHI, and RNase Y. Ribonuclease T2 [EC 3.1.27.1] is also known as ribonuclease II. 

It is worth a pause, however, to consider how such models should best be used. Part of the motivation for developing linear scaling models has been to permit QM calculations to be carried out on biomolecules, e.g., proteins or polynucleic acids. However, one may legitimately ask whether there is any point in such a calculation, beyond demonstrating that... 

Hafez IM, Maurer N, Cullis PR (2001) On the mechanism whereby cationic lipids promote intracellular delivery of polynucleic acids. Gene Ther 8 1188-1196... 

The study of photoinduced ET in covalently linked donor-acceptor assemblies began with comparatively simple dyad systems which contain a transition metal center covalently linked to a single electron donor or acceptor unit [26]. However, work in this area has naturally progressed and in recent years complex supramolecular assemblies comprised of one or more metal complexes that are covalently linked to one or more organic electron donors or acceptors have been synthesized and studied [27-36]. Furthermore, several groups have utilized the useful photoredox properties of transition metal complexes to probe electron and energy transfer across spacers comprised of biological macromolecules such as peptides [37,38], proteins [39,40], and polynucleic acids [41]. 

The above discussion dealt primarily with synthetic polyelectrolytes, which behave in solution more or less as flexible polymers. Another important group, the natural polyelectrolytes, will not be discussed here. They include polynucleic acids, proteins, carbohydrate derivates, etc. They generally behave as rigid-chain polymers, due to their helix conformation. 

Individual sequential covalent bond formation in a series of reaction-isolation steps. Bond formation usually involves only one or several connections per step. The method can be used to construct one-dimensional linear structures (e.g., polypeptides/polynucleic acids) where chronological sequencing can be used to introduce desired side groups or chirality by this linear covalent method. 

The luminescence properties of polynucleic acids and proteins have been reviewed in detail previously. However recent time-resolved studies have important implications for existing concepts of the excited states of biopolymers. The readily observable luminescence from proteins at room temperature has made these systems particularly attractive to study. The fluorescence properties of the arrxnatic amino acid zwitter-ions which determine the emission from proteins are summarised in Table 11. The wide range of emission maxima observed in proteins (ranging from 308 nm in azurin to 342 nm in lysozyme) has been exfdained by many authors to reflect the different environments of the tryptophan residues in the proteins However, it is now... 

The existence of electronic energy transfer between the chromr hores in proteins and polynucleic acids is another question that has been discussed by authors over the years For proteins there is substantial evidence from steady state luminescence data that energy transfer occurs in the sequence phenylalanine... 

By far the deepest and most impressively detailed advance of biology by NMR has been its use to determine three-dimensional molecular structures in solution of proteins, polynucleic acids and even polysaccharides. This molecular level of understanding has helped explain at the molecular level how certain enzymes promote their very specific bond breakings or makings, how cancer agents intercalate with DNA, how inhibitors bind to enzymes and a host of other biological phenomena. 

A specific feature of polymers and the major difference to naturally occurring proteins and polynucleic acids is their dispersity. This can account on the one hand for the chemical composition in copolymers, whereby each individual chain may have a different sequence of the comonomers (= isomers). However, it is especially prominent when one looks at the molar mass. The statistic nature of the polymerization process always results in a mixture of maaomol-ecules of different lengths with a specific distribution in molar mass. 

The latter class of bioorganic materials has gained momentum during the recent years, mainly because many functions have been implemented and potential applications realized [4]. The combination of nucleic acids with conjugated polymers [5] or electroactive macromolecules [6] has resulted in highly sensitive and selective probes, whilst equally important are polynucleic acids that are coimected covalently to thermoresponsive polymers such hybrids have been used successfully for the purification of plasmid DNA [7] and DNA-binding proteins [8]. 

It has been proposed that these nanometer- and micrometer-sized particles may have applications in biology in sensing and imaging applications or as delivery vehicles (De et al, 2008). The unique properties of nanoparticles such as their similar size to biomolecules such as proteins and polynucleic acids, as well as their ability to be tuned to contain a range of functional materials such as metal centers, dye molecules, etc. make them attractive candidates for biological and materials applications. The applicable of these nanoparticle platforms for therapeutic and diagnostic activities relies on the functionalization and also encapsulation potential of these materials. 

Aiming toward the functional applications of DNA as novel molecular devices, polynucleic acids have been immobilized as two-dimensional molecular assemblies by means of the specific intermolecular interaction at the air-water interface [82,83] as well as by the polyion complex technique [84]. We describe here the effect of DNA on photoinduced electron transfer in polyion complex LB monolayers deposited on an ITO electrode [85], or cast in polyion complex films [86]. 

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