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Hodder Revision Guide Biology: 6 Nucleic acids and …
Since nucleic acids were limited to the chromosomes of the nucleus, they were generally accepted as the material basis of inheritance. That correct view came into question in the 1920s, however, as more was learned about nucleic acid structure. From its chemical analysis, () was interpreted to be a monotonous repeating polymer of only four nucleotides. That such a simple structure could encode sufficient information for directing cellular functions and development, therefore, seemed unlikely. Attention was then turned to proteins, which are diverse in type and complexity. The view that proteins are the genetic material temporarily supplanted the role earlier and correctly assigned to nucleic acids. See also
Utilization of the genetic information encoded in the nucleotide sequences of genes involves a series of steps and uses a variety of enzymes and auxiliary proteins. Though both strands of the duplex carry information, only one, the sense strand, is used to direct cellular functions. This is done first by unwinding the duplex and making an copy, a transcript, of a gene. This involves the localized action of topoisomerases and polymerase, along with a variety of transcription factors. The original transcript of a gene encoding a polypeptide is then processed into messenger , which is transported to the cytoplasm for translation on ribosomes. Translation results in the synthesis of a polypeptide chain, the amino acid sequence of which has been specified by the nucleotide sequence of the particular gene. Other RNAs include ribosomal , major structural components of ribosomes, transfer RNAs that transport amino acids to the ribosomes during translation; also mitochondrial and plastid RNAs encoded by genes in those cytoplasmic bodies. See also , and
Nucleic acids have roles in the storage and ..
The experiments of Griffith were subsequently confirmed by other investigators, and in 1931 Dawson and Sia succeeded in inducing transformation in vitro. It was not until 1944, however, that Avery, MacLeod and McCarty identified as the agent responsible for bacterial transformation. Even then there was some reluctance among scientists to assign to nucleic acids the role of the genetic material. The experiments of Avery and his colleagues marked a turning point, however, because the purification procedures and the control steps they employed to eliminate an active role for all but trace contaminants were quite convincing. Their experiments utilized encapsulated (S) type III pneumococci, from which they isolated a very highly purified fraction. That fraction was capable of transforming unencapsulated (R) variants of type II cells into fully encapsulated cells of type III, from which the was isolated. One key to eliminating any role of molecules other than in the transformation process was the use of the enzyme deoxyribonuclease (DNAase), which depolymerizes DNA. Avery et al. showed that treating the active transforming fraction with the nuclease destroyed the structure of and the ability of that fraction to transform pneumococcus cells. Treatments with enzymes that attack other cellular components had no effect on transformation activity.
Nucleic Acids and Polypeptides ..
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