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1.
The paper presents a model of coevolution of short peptides (P) and short oligonucleotides (N) at an early stage of chemical evolution leading to the origin of life. The model describes polymerization of both P and N types of molecules on mineral surfaces in aqueous solution at moderate temperatures. It is assumed that amino acid and nucleotide monomers were available in a prebiotic milieu, that periodic variation in environmental conditions between dry/warm and wet/cool took place and that energy sources were available for the polymerization. An artificial chemistry approach in combination with agent-based modeling was used to explore chemical evolution from an initially random mixture of monomers. It was assumed that the oligonucleotides could serve as templates for self-replication and for translation of peptide compositional sequences, and that certain peptides could serve as weak catalysts. Important features of the model are the short lengths of the peptide and oligonucleotide molecules that prevent an error catastrophe caused by copying errors and a finite diffusion rate of the molecules on a mineral surface that prevents excessive development of parasitism. The result of the simulation was the emergence of self-replicating molecular systems consisting of peptide catalysts and oligonucleotide templates. In addition, a smaller but significant number of molecules with alternative compositions also survived due to imprecise reproduction and translation of templates providing variability for further evolution. In a more general context, the model describes not only peptide-oligonucleotide molecular systems, but any molecular system containing two types of polymer molecules: one of which serves as templates and the other as catalysts.The presented coevolutionary system suggests a possible direction towards finding the origin of molecular functionality in a prebiotic environment.  相似文献   

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Most experimental work on the origin of life has focused on either characterizing the chemical synthesis of particular biochemicals and their precursors or on designing simple chemical systems that manifest life-like properties such as self-propagation or adaptive evolution. Here we propose a new class of experiments, analogous to artificial ecosystem selection, where we select for spontaneously forming self-propagating chemical assemblages in the lab and then seek evidence of a response to that selection as a key indicator that life-like chemical systems have arisen. Since surfaces and surface metabolism likely played an important role in the origin of life, a key experimental challenge is to find conditions that foster nucleation and spread of chemical consortia on surfaces. We propose high-throughput screening of a diverse set of conditions in order to identify combinations of “food,” energy sources, and mineral surfaces that foster the emergence of surface-associated chemical consortia that are capable of adaptive evolution. Identification of such systems would greatly advance our understanding of the emergence of self-propagating entities and the onset of adaptive evolution during the origin of life.  相似文献   

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Steps by which a nonliving chemical system could have transformed into a living system are described and discussed, assuming general features of Wächtershäuser's chemo-autotrophic surface theory of the origin of life. Environmental species such as CO2 and H2S are proposed to have reacted to form a quasi-steady state metal-bound intermediate (CH3-M) that slowly decayed into waste (CH4). Unpredictable dispersive reactions expanded the system to include surface-bound forms of the citric acid cycle intermediates (oxaloacetate → citrate). Further reaction yielded an autocatalytic system in which raw materials are converted into the system at exponential rates. Combinatorial dispersive reactions that improved the performance of this system were automatically selected and incorporated into it. Systems evolved critical features of living systems (proteins, membranes, proteins, nucleic acids, etc.) using two related mechanisms called grafting and waste-conversion. Such living systems were transformed from less recognizable types (characterized by autocatalytic spreading, decentralization, poorly defined boundaries, etc.) into more recognizable ones (encapsulated by membranes, controlled by single-molecule genomes, etc.) that self-replicated by a cell division cycle and could evolve by the standard gene-based Darwinian mechanism. The resulting systems are viewed as having an autocatalytic network composed of three linked autocatalytic subreactions.  相似文献   

5.
Sixty-three compounds were isolated and identified from heated starch and from heated starch with glycine. Starch or starch with glycine was heated in an Erlenmeyer flask at 290°C under a nitrogen stream. The volatiles formed during heating were entrained on a porous polymer (Porapack Q). Residual charred materials in the flasks were extracted with methylene chloride. The oily dark brown materials recovered from both the Porapack Q traps and the methylene chloride extracts were subjected to gas chromatography and gas chromatography/mass spectrometry. The compounds identified include 3 hydrocarbons, 11 ketones, 3 aldehydes, 24 aromatic compounds, 10 furans and 12 nitrogen-containing compounds. Formation mechanisms of some major products are proposed.  相似文献   

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The major histocompatibility complex (MHC) is a dynamic genomic region with an essential role in the adaptive immunity of jawed vertebrates. The evolution of the MHC has been dominated by gene duplication and gene loss, commonly known as the birth-and-death process. Evolutionary studies of the MHC have mostly focused on model species. However, the investigation of this region in non-avian reptiles is still in its infancy. To provide insights into the evolutionary mechanisms that have shaped the diversity of this region in the Order Crocodylia, we investigated MHC class I exon 3, intron 3, and exon 4 across 20 species of the families Alligatoridae and Crocodilidae. We generated 124 DNA sequences and identified 31 putative functional variants as well as 14 null variants. Phylogenetic analyses revealed three gene groups, all of which were present in Crocodilidae but only one in Alligatoridae. Within these groups, variants generally appear to cluster at the genus or family level rather than in species-specific groups. In addition, we found variation in gene copy number and some indication of interlocus recombination. These results suggest that MHC class I in Crocodylia underwent independent events of gene duplication, particularly in Crocodilidae. These findings enhance our understanding of MHC class I evolution and provide a preliminary framework for comparative studies of other non-avian reptiles as well as diversity assessment within Crocodylia.  相似文献   

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Monthly variations of some physical and chemical characteristics of Nile waters at Assiut (375 km south from Cairo, Egypt) during the period from September 1980 to September 1982 were followed and discussed. As expected, the maximum temperature was recorded in summer and the minimum in winter. The pH values of Nile waters were recorded to be in the vicinity of 8.0. The highest oxygen concentrations were recorded in the summer months, mainly due to the relatively high photosynthetic activity. The total soluble salts and the total alkalinity exhibited almost identical trends. Nitrate, phosphate, silicate and chloride concentrations showed no major regular trends. The cation abundances by weight were as follows: Ca2+ > Na+ > Mg2+ > K+.  相似文献   

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Dihydro-α-ionol (II) was converted to dihydro-α-ionyl bromide (III) and dihydro-α-ionyl tosylate (V), which afforded their Wittig reagents (IV), (VI) on heating with triphenylphosphine. The Wittig reaction of ambreinolal-tetrahydropyranylether (VII) with the above Wittig reagents (IV) or (VI) gave α-ambrein-tetrahydropyranylether (VIII).  相似文献   

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So called ambreinolal (IV),* a component of ambergris, was first synthesized by CrO3 oxidation of ambreinolol (III)* which was obtained from ambreinolide (II) by reduction with LiAlH4. Ambreinolol (III) was converted to the C17-saturated oxide (VII) in a good yield through the monotosylate (VIII) by treatment with p-toluenesulfonyl chloride in pyridine.

Ambrein (I), a major constituent of ambergris, was easily converted to ambrein-tetrahydropyranylether (II), of which thermal decomposition gave back ambrein (I). The tetrahydropyranylether (II) was oxidized to ambreinolal-tetrahydropyranylether (V) in two steps. Ambreinolal-tetrahydropyranylether (V) was synthesized from ambreinolol (VII) in four steps and converted to the C17-unsaturated oxide (VI) on heating.  相似文献   

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Allethrin-(E)-Ol (IV), allethrin-(E)-al (V) and allethrin-(E)-acid (VI), the metabolites of allethrin (III) in the insect body, were synthesized. Their low toxicities to houseflies seem to support the hypothesis that they are products of the detoxication process of allethrin.  相似文献   

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Methanogens are a phylogenetically diverse group belonging to Euryarchaeota. Previously, phylogenetic approaches using large datasets revealed that methanogens can be grouped into two classes, “Class I” and “Class II”. However, some deep relationships were not resolved. For instance, the monophyly of “Class I” methanogens, which consist of Methanopyrales, Methanobacteriales and Methanococcales, is disputable due to weak statistical support. In this study, we use MSOAR to identify common orthologous genes from eight methanogen species and a Thermococcale species (outgroup), and apply GRAPPA and FastME to compute distance-based gene order phylogeny. The gene order phylogeny supports two classes of methanogens, but it differs from the original classification of methanogens by placing Methanopyrales and Methanobacteriales together with Methanosarcinales in Class II rather than with Methanococcales. This study suggests a new classification scheme for methanogens. In addition, it indicates that gene order phylogeny can complement traditional sequence-based methods in addressing taxonomic questions for deep relationships.  相似文献   

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黄瓜化学成分的提取与研究   总被引:2,自引:0,他引:2  
本文分别采用减压蒸馏-冷冻浓缩、微波-超声波萃取和固相微萃取(SPME)技术,对鲜黄瓜(带皮)、黄瓜皮、肉、籽进行了化学成分的提取及气相色谱-质谱(GC-MS)分析,共检测出109种化合物,其中大部分化合物尚未从黄瓜中分离得到.实验结果证明黄瓜皮及黄瓜籽中含有较多芳香类物质、生育酚、角鲨烯、姜烯、阿茶碱、亚油酸与油酸等营养物质.  相似文献   

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采用正反相硅胶、Sephadex LH-20凝胶、MCI树脂等层析技术从中药益智95%乙醇提取物的乙酸乙酯部位分离得到13个化合物,运用现代波谱技术分别鉴定为:益智酮甲(1,yakuchinone A)、益智醇(2,oxyphyllacin-ol)、白杨素(3,chrysin)、rhamnocitrin(4)、oxyphyllenodiol A(5)、oxyphyllenodiol B(6)、nootkatone(7)、dehydro-noot-katone(8)、7-epi-teucrenone(9)、oxyphyllenone A(10)、oxyphyllenone B(11)、原儿茶酸(12,protocatechuic acid)和琥珀酸(13,succinic acid)。其中化合物4、13为首次从该植物中分得,化合物8为新的天然产物。  相似文献   

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J. R. Augustine 《CMAJ》1967,96(20):1367-1370
Laboratory studies on 109 acutely intoxicated male and female alcoholics admitted to the general medical wards of a community general hospital were undertaken. Initially the program was designed to study the thyroid function of these patients, as a previous report had noted that large numbers of alcoholics were thyroid-deficient. During the study, however, other laboratory examinations, which might be confusing or misleading in alcoholics, were also measured. These additional estimations included the serum glutamic oxaloacetic transaminase (SGOT), the serum cholesterol and the serum amylase. No patients were found to be hypothyroid. The results of the tests indicate the need for caution in interpreting SGOT and serum amylase results in acute alcoholics.  相似文献   

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枸骨叶的化学成分研究   总被引:1,自引:0,他引:1  
采用溶剂提取和柱层析色谱分离,根据化合物理化性质和光谱数据鉴定其结构.结果从枸骨叶中分离得到9个化合物,分别为羽扇豆醇(1)、3,28-乌苏酸二醇(2)、熊果酸(3)、异鼠李黄素(4)、山奈酚-3-O-β-D-葡萄糖苷(5)、地榆苷Ⅰ(6)、槲皮苷-3-O-β-D-葡萄糖苷(7)、异鼠李素-3-O-β-D-葡萄糖苷(8)、冬青苷Ⅱ(9).化合物7和8为首次从冬青属植物中分离得到,化合物5为首次从该植物中分离得到,同时首次报道了化合物9的13CNMR数据.  相似文献   

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从沙针乙醇提取物的乙酸乙酯部分分离得到11个化合物,它们的结构经波谱分析鉴定为(+)儿茶素(1)、(+)-afzelechin-3-氧-L-鼠李糖(2)、afzelechin-(4α-8)-儿茶素(3)、(+)-儿茶素-3-氧-L-鼠李糖(4)、二氢山奈酚3-氧-L鼠李糖(5)、反式-植醇(6)、24-乙基胆甾烷-5,22.二烯-3β-醇-棕榈酸酯(7)、2.十八烯酸(8)、芒柄花萜醇(9)、3β-谷甾醇(10)、胡萝卜苷(11).化合物1~11为首次从该属植物中分离得到.  相似文献   

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