Replication, of nucleic acids

Thus it was necessary to develop models which would make self-replication of nucleic acids possible. Such models would need to be simple, since they should simulate prebiotic processes (von Kiedrowski, 1999). The realisation of such a scheme would require the fulfilment of several conditions ... 

We still need to clear up one or two points of nomenclature in normal replication of nucleic acids, the matrix (the + strand) and the newly formed daughter strand (- strand) are held together by Watson-Crick hydrogen bonding. This process is also referred to as cross-catalytic . Normal autocatalysis is different it leads to a product which corresponds in structure to the matrix, so that there is no difference between the + and - strands. Such self-complementary sequences are called palindromes. 

From the complementary duplex structure of DNA described in chapter 25, it is a short intuitive hop to a model for replication that satisfies the requirement for one round of DNA duplication for every cell division. In chapter 26, DNA Replication, Repair, and Recombination, key experiments demonstrating the semiconservative mode of replication in vivo are presented. This is followed by a detailed examination of the enzymology of replication, first for how it occurs in bacteria and then for how it occurs in animal cells. Also included in this chapter are select aspects of the metabolism of DNA repair and recombination. The novel process of DNA synthesis using RNA-directed DNA polymerases is also considered. First discovered as part of the mechanisms for the replication of nucleic acids in certain RNA viruses, this mode of DNA synthesis is now recognized as occurring in the cell for certain movable genetic segments and as the means whereby the ends of linear chromosomes in eukaryotes are synthesized. 

All life forms require polymerases for replication of nucleic acids. DNA polymerases from various life forms [8] as well as reverse transcriptase from HIV [9] are all activated by two metal ions, which are thought to provide three types of activation, i.e. Lewis acid, metal-hydroxide and leaving group [Figure 6.26(A)], The Klenow fragment of DNA polymerase I is a 3, 5 -exonuclease that is involved in editing the growing... 

Second, autocatalytic replication of nucleic acids led to selection. Thus, life apparently emerged from inorganic nonliving matter. 

As a final note, there is the observation that antiviral agents act to inhibit the replication of nucleic acids. There is a connection with anticancer agents, which are enzyme inhibitors for DNA processes. In a way, the connection is obvious, in view of the fact that viruses are but pieces of DNA. A search of Medline indicates that antiviral agents being cUnically tested include inhibitors for the enzymes called nucleoside phosphorylases and M-deoxyribosylttansferases. 

Autocatalytic systems have been proposed to be instigator of the first life. In this example the autocatalytic replication of nucleic acids generates the nucleic acid template for its own reproduction (55) in this case a hexadeoxynucleotide replicates. In the optimal case the autocatalytic system replicates exponentially resulting in a very rapid build up of the nucleotide. Exponential growth has not been attained in autocatalytic systems proposed to initiate the first life 66). 

Weizmann, Y., Cheglakov, Z., Pavlov, V., Willner, I. (2006a). Autonomous fueled mechanical replication of nucleic acid templates for the amplified optical detection of DNA. Angew Chem Int Ed Engl 45, 2238-2242. 

The ability to biocatalyze the replication of nucleic acids on surfaces (see Sec. V. A) and the ampUflcation of DNA recognition events on electronic transducers by the biocatalyzed precipitation of an insoluble product on the transducer in the presence of an enzyme conjugate (see Sec. IV. B), suggest that amplified detection of DNA on surfaces may be achieved by the replication of DNA while tagging. Indeed, the amplified detection of genomic DNA or RNA was accomplished by polymerase-induced replication of the biotin-tagged DNA or RNA, followed by the biocatalyzed precipitation of an insoluble product on the transducer [48]. 

Well before life arrived on Earth, however, a self-replicating process was necessary. How It seems reasonable to suppose that specific nucleic acid-nucleic acid and nucleic acid-protein interactions were of fundamental importance for the replication of nucleic acids and the evolution of the genetic code (48). Such recognition processes are dependent on base sequence and amino acid sequence. According to R. D. MacElroy from NASA, these would probably play a key role in the formation of protein nucleic acid complexes. 

All organisms share basic developmental processes such as membrane synthesis, cell division, replication of nucleic acids, and ribosome-mediated protein synthesis. 

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