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41.
It is generally thought that, in order to compensate for lower solar flux and maintain liquid oceans on the early Earth, methane must have been an important greenhouse gas before approximately 2.2 billion years (Gyr) ago. This is based upon a simple thermodynamic calculation that relates the absence of siderite (FeCO3) in some pre-2.2-Gyr palaeosols to atmospheric CO2 concentrations that would have been too low to have provided the necessary greenhouse effect. Using multi-dimensional thermodynamic analyses and geological evidence, we show here that the absence of siderite in palaeosols does not constrain atmospheric CO2 concentrations. Siderite is absent in many palaeosols (both pre- and post-2.2-Gyr in age) because the O2 concentrations and pH conditions in well-aerated soils have favoured the formation of ferric (Fe3+)-rich minerals, such as goethite, rather than siderite. Siderite, however, has formed throughout geological history in subsurface environments, such as euxinic seas, where anaerobic organisms created H2-rich conditions. The abundance of large, massive siderite-rich beds in pre-1.8-Gyr sedimentary sequences and their carbon isotope ratios indicate that the atmospheric CO2 concentration was more than 100 times greater than today, causing the rain and ocean waters to be more acidic than today. We therefore conclude that CO2 alone (without a significant contribution from methane) could have provided the necessary greenhouse effect to maintain liquid oceans on the early Earth. 相似文献
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Phosphates would probably have been essential compounds for prebiotic evolution on the primitive Earth. In this context, there have been several studies of condensation of water-soluble phosphates to polyphosphates and phosphorylation and condensation or polymerization of biomolecules with polyphosphates. But most of the phosphorus on the early Earth would have been in the form of water-insoluble apatite, and the origin of the water-soluble polyphosphates required for prebiotic evolution has therefore been a mystery. Here we show, both from experiments that simulate magmatic conditions and from analysis of volatile condensates in volcanic gas, that volcanic activity can produce water-soluble polyphosphates through partial hydrolysis of P4O10. This mechanism seems to be the only viable route identified so far for the production of these species on the primitive Earth. 相似文献
44.
Willer CJ Sanna S Jackson AU Scuteri A Bonnycastle LL Clarke R Heath SC Timpson NJ Najjar SS Stringham HM Strait J Duren WL Maschio A Busonero F Mulas A Albai G Swift AJ Morken MA Narisu N Bennett D Parish S Shen H Galan P Meneton P Hercberg S Zelenika D Chen WM Li Y Scott LJ Scheet PA Sundvall J Watanabe RM Nagaraja R Ebrahim S Lawlor DA Ben-Shlomo Y Davey-Smith G Shuldiner AR Collins R Bergman RN Uda M Tuomilehto J Cao A Collins FS Lakatta E Lathrop GM Boehnke M Schlessinger D Mohlke KL 《Nature genetics》2008,40(2):161-169
To identify genetic variants influencing plasma lipid concentrations, we first used genotype imputation and meta-analysis to combine three genome-wide scans totaling 8,816 individuals and comprising 6,068 individuals specific to our study (1,874 individuals from the FUSION study of type 2 diabetes and 4,184 individuals from the SardiNIA study of aging-associated variables) and 2,758 individuals from the Diabetes Genetics Initiative, reported in a companion study in this issue. We subsequently examined promising signals in 11,569 additional individuals. Overall, we identify strongly associated variants in eleven loci previously implicated in lipid metabolism (ABCA1, the APOA5-APOA4-APOC3-APOA1 and APOE-APOC clusters, APOB, CETP, GCKR, LDLR, LPL, LIPC, LIPG and PCSK9) and also in several newly identified loci (near MVK-MMAB and GALNT2, with variants primarily associated with high-density lipoprotein (HDL) cholesterol; near SORT1, with variants primarily associated with low-density lipoprotein (LDL) cholesterol; near TRIB1, MLXIPL and ANGPTL3, with variants primarily associated with triglycerides; and a locus encompassing several genes near NCAN, with variants strongly associated with both triglycerides and LDL cholesterol). Notably, the 11 independent variants associated with increased LDL cholesterol concentrations in our study also showed increased frequency in a sample of coronary artery disease cases versus controls. 相似文献
45.
Masataka Watanabe 《科学通报(英文版)》2005,50(7):679-684
Land and sea are linked closely by large rivers throughrunoff and sediment discharging and biochemical materialtransferring into the sea[1?3]. The processes carried out byenergy exchange have been in a sensitive response toglobal change[4]. To study the mechanism of sediment transport in the river basin as to reflecting hydromor- phological and climatological controls is thus becoming vital for earth scientists, at present and in the near future since any change in fluvial landform is of a gre… 相似文献
46.
Almost all aphid species (Homoptera, Insecta) have 60-80 huge cells called bacteriocytes, within which are round-shaped bacteria that are designated Buchnera. These bacteria are maternally transmitted to eggs and embryos through host generations, and the mutualism between the host and the bacteria is so obligate that neither can reproduce independently. Buchnera is a close relative of Escherichia coli, but it contains more than 100 genomic copies per cell, and its genome size is only a seventh of that of E. coli. Here we report the complete genome sequence of Buchnera sp. strain APS, which is composed of one 640,681-base-pair chromosome and two small plasmids. There are genes for the biosyntheses of amino acids essential for the hosts in the genome, but those for non-essential amino acids are missing, indicating complementarity and syntrophy between the host and the symbiont. In addition, Buchnera lacks genes for the biosynthesis of cell-surface components, including lipopolysaccharides and phospholipids, regulator genes and genes involved in defence of the cell. These results indicate that Buchnera is completely symbiotic and viable only in its limited niche, the bacteriocyte. 相似文献
47.
Tabata S Kaneko T Nakamura Y Kotani H Kato T Asamizu E Miyajima N Sasamoto S Kimura T Hosouchi T Kawashima K Kohara M Matsumoto M Matsuno A Muraki A Nakayama S Nakazaki N Naruo K Okumura S Shinpo S Takeuchi C Wada T Watanabe A Yamada M Yasuda M Sato S de la Bastide M Huang E Spiegel L Gnoj L O'Shaughnessy A Preston R Habermann K Murray J Johnson D Rohlfing T Nelson J Stoneking T Pepin K Spieth J Sekhon M Armstrong J Becker M Belter E Cordum H Cordes M Courtney L Courtney W Dante M Du H 《Nature》2000,408(6814):823-826
The genome of the model plant Arabidopsis thaliana has been sequenced by an international collaboration, The Arabidopsis Genome Initiative. Here we report the complete sequence of chromosome 5. This chromosome is 26 megabases long; it is the second largest Arabidopsis chromosome and represents 21% of the sequenced regions of the genome. The sequence of chromosomes 2 and 4 have been reported previously and that of chromosomes 1 and 3, together with an analysis of the complete genome sequence, are reported in this issue. Analysis of the sequence of chromosome 5 yields further insights into centromere structure and the sequence determinants of heterochromatin condensation. The 5,874 genes encoded on chromosome 5 reveal several new functions in plants, and the patterns of gene organization provide insights into the mechanisms and extent of genome evolution in plants. 相似文献
48.
Hattori M Fujiyama A Taylor TD Watanabe H Yada T Park HS Toyoda A Ishii K Totoki Y Choi DK Groner Y Soeda E Ohki M Takagi T Sakaki Y Taudien S Blechschmidt K Polley A Menzel U Delabar J Kumpf K Lehmann R Patterson D Reichwald K Rump A Schillhabel M Schudy A Zimmermann W Rosenthal A Kudoh J Schibuya K Kawasaki K Asakawa S Shintani A Sasaki T Nagamine K Mitsuyama S Antonarakis SE Minoshima S Shimizu N Nordsiek G Hornischer K Brant P Scharfe M Schon O Desario A Reichelt J Kauer G Blocker H 《Nature》2000,405(6784):311-319
Chromosome 21 is the smallest human autosome. An extra copy of chromosome 21 causes Down syndrome, the most frequent genetic cause of significant mental retardation, which affects up to 1 in 700 live births. Several anonymous loci for monogenic disorders and predispositions for common complex disorders have also been mapped to this chromosome, and loss of heterozygosity has been observed in regions associated with solid tumours. Here we report the sequence and gene catalogue of the long arm of chromosome 21. We have sequenced 33,546,361 base pairs (bp) of DNA with very high accuracy, the largest contig being 25,491,867 bp. Only three small clone gaps and seven sequencing gaps remain, comprising about 100 kilobases. Thus, we achieved 99.7% coverage of 21q. We also sequenced 281,116 bp from the short arm. The structural features identified include duplications that are probably involved in chromosomal abnormalities and repeat structures in the telomeric and pericentromeric regions. Analysis of the chromosome revealed 127 known genes, 98 predicted genes and 59 pseudogenes. 相似文献
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