RESUMO
A manuscript on allostery signed by Francis Crick and Jeffries Wyman was sent by Crick to Jacques Monod in 1965. Monod transmitted a copy of the manuscript, upon which he had written several comments, to Jean-Pierre Changeux, then a post-doctoral fellow at the University of California Berkeley in the laboratory of Howard Schachman. Changeux provided a copy to Stuart Edelstein, a graduate student in the same laboratory. The manuscript was never submitted for publication, but Edelstein retained his copy since that time and has edited it for publication in the special issue on allostery. The text emphasized the interpretation of the properties of an allosteric oligomer by characterizing its equivalent monomer. The text also developed the concept of the allosteric range and included a simple equation for calculation of the Hill coefficient from the parameters of the Monod-Wyman-Changeux model.
Assuntos
Proteínas/história , Regulação Alostérica , História do Século XX , Ligantes , Modelos MolecularesAssuntos
DNA Circular , DNA Super-Helicoidal , Modelos Químicos , Replicação do DNA , DNA Topoisomerases Tipo I/metabolismo , DNA Circular/metabolismo , DNA Super-Helicoidal/metabolismo , DNA Viral/metabolismo , Eletroforese em Gel de Ágar , Etídio/farmacologia , Matemática , Microscopia Eletrônica , Conformação de Ácido Nucleico/efeitos dos fármacos , Polyomavirus/genéticaRESUMO
The DNA of higher organisms usually falls into two classes, one specific and the other comparatively nonspecific. It seems plausible that most of the latter originates by the spreading of sequences which had little or no effect on the phenotype. We examine this idea from the point of view of the natural selection of preferred replicators within the genome.
Assuntos
Evolução Biológica , DNA/genética , Animais , Sequência de Bases , Replicação do DNA , Metabolismo Energético , Genes , Genes Reguladores , Humanos , Fenótipo , RNA Nuclear Heterogêneo/genética , RNA Mensageiro/genética , Seleção Genética , Fatores de TempoRESUMO
Two methods have been used to measure the single-strand lengths of the DNA fragments produced by deoxyribonuclease I digestion of chromatin. The average lengths obtained are muliples of about 10.4 bases, significantly different from the value of 10 previously reported. This periodicity in fragment lengths is closely related to the periodicity of the DNA double helix in chromatin, but the two values need not be exactly the same.
Assuntos
Cromatina/ultraestrutura , Desoxirribonucleases/metabolismo , Animais , Sequência de Bases , Cromatina/metabolismo , Hidrólise , Peso Molecular , RatosRESUMO
From observations on the partial disintegration of isolated human metaphase chromosomes we propose that human metaphase chromatids have a rather simple organization based on the folding and coiling of a long, regular, hollow cylindrical structure with a diameter of about 4000 A. This cylindrical structure, the unit fiber, is postulated to be a super-solenoid formed by the coiling of a 300 A solenoid, itself composed by coiling the basic string of nucleosomes. The structure of a human chromatid would thus be a hierarchy of helices, the contraction ratio of each coil, in ascending order of size, being approximately 7, 6, 40, and 5. This model appears to explain the estimated mass/unit length and accounts for many of the known features of human mitotic chromatids.
Assuntos
Cromossomos/ultraestrutura , Mitose , Cromossomos/fisiologia , DNA , Feto , Fibroblastos , Humanos , Microscopia Eletrônica , Conformação de Ácido NucleicoRESUMO
It is suggested that protein sythesis may have begun without even a primitive ribosome if the primitive tRNA could take up two configuration and could bind to the messenger RNA with five base-pairs instead of the present three. This idea would impose base sequence restriction on the early messages and on the early genetic code such that the first four amino acids coded were glycine, serine, aspartic acid and aspargine. A possible mechanism is suggested for the polymerization of the early message.
Assuntos
Modelos Biológicos , Biossíntese de Proteínas , RNA Mensageiro/metabolismo , RNA de Transferência/metabolismo , Anticódon , Códon , Código Genético , Conformação de Ácido Nucleico , RNA Mensageiro/biossíntese , Ribossomos/metabolismo , Relação Estrutura-Atividade , Moldes GenéticosRESUMO
In considering supercoils formed by closed double-stranded molecules of DNA certain mathematical concepts, such as the linking number and the twist, are needed. The meaning of these for a closed ribbon is explained and also that of the writhing number of a closed curve. Some simple examples are given, some of which may be relevant to the structure of chromatin.
