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61.
T D Schneider 《Journal of theoretical biology》1991,148(1):125-137
Single molecules perform a variety of tasks in cells, from replicating, controlling and translating the genetic material to sensing the outside environment. These operations all require that specific actions take place. In a sense, each molecule must make tiny decisions. To make a decision, each "molecular machine" must dissipate an energy Py in the presence of thermal noise Ny. The number of binary decisions that can be made by a machine which has dspace independently moving parts is the "machine capacity" Cy = dspace log2 [(Py + Ny)/Ny]. This formula is closely related to Shannon's channel capacity for communications systems, C = W log2 [(P + N)/N]. This paper shows that the minimum amount of energy that a molecular machine must dissipate in order to gain one bit of information is epsilon min = kB T ln (2) joules/bit. This equation is derived in two distinct ways. The first derivation begins with the Second Law of Thermodynamics, which shows that the statement that there is a minimum energy dissipation is a restatement of the Second Law of Thermodynamics. The second derivation begins with the machine capacity formula, which shows that the machine capacity is also related to the Second Law of Thermodynamics. One of Shannon's theorems for communications channels is that as long as the channel capacity is not exceeded, the error rate may be made as small as desired by a sufficiently involved coding. This result also applies to the dissipation formula for molecular machines. So there is a precise upper bound on the number of choices a molecular machine can make for a given amount of energy loss. This result will be important for the design and construction of molecular computers. 相似文献
62.
63.
"Hemobilia," upper gastrointestinal tract bleeding that originates from within the biliary tract, has become widely recognized due to an increased clinical awareness of the disorder and to improvements in diagnostic techniques. In addition, the growing use of percutaneous liver puncture for the diagnosis of and therapy for hepatobiliary diseases and the increased incidence of both blunt and penetrating hepatic trauma have contributed to a rising incidence of hemobilia. We review the history, pathophysiology, and current approaches to the diagnosis and treatment of this disease. 相似文献
64.
Localization of growth arrest-specific genes on mouse Chromosomes 1, 7, 8, 11, 13, and 16 总被引:5,自引:0,他引:5
Mario P. Colombo Alessia Martinotti Thad A. Howard Claudio Schneider Peter D'Eustachio Michael F. Seldin 《Mammalian genome》1992,2(2):130-134
Growth arrest in NIH3T3 cells is associated with increased expression of a variety of mRNAs, several of which have been isolated as cDNA clones. Six of these growth arrest-specific (Gas) genes were mapped by following the inheritance of DNA restriction fragment length variants (RFLVs) associated with them in panels of recombinant inbred (RI) strains of mice and in the progeny of backcrosses both between laboratory mouse strains and between a laboratory strain and Mus spretus. The six genes are unlinked. Gas-1 maps to Chromosome (Chr) 13, Gas-2 to Chr 7, Gas-3 to Chr 11, Gas-4 to Chr 16, Gas-6 to Chr 8, and Gas-10 to Chr 1. 相似文献
65.
Stephan Schneider Albrecht Fischer Adriaan W.C. Dorresteijn 《Development genes and evolution》1992,201(4):243-256
Summary Early development of Platynereis massiliensis was studied in serial sections of fixed embryos and in living or fixed embryos whose nuclei had been made visible with a fluorescent label. The unfertilized egg is an ellipsoid with three axes of differing length. The longest axis corresponds to the dorsoventral axis of the developing embryo. Egg volume is ten times that in the sibling species, P. dumerilii, mainly due to increased yolk content. The timing and spatial pattern of cleavage were observed from first cleavage to the 62-cell stage. Volumes of the blastomeres, their nuclei, their yolk-free cytoplasm and their yolk were determined from serial sections up to the 29-cell stage. In the P. massiliensis embryo, cell cycles are on average 3.7 times longer than in P. dumerilii; volume proportions among the blastomeres also differ and the macromeres containing the bulk of yolk are particularly large, but otherwise the cleavage patterns, differential segregation of yolk and yolk-free cytoplasm, and the histogenetic fates of the blastomeres are the same as in P. dumerilii. This equivalence of cell lineage and of cytoplasmic segregation mechanisms in both species, maintained in spite of the different appearance of the embryos, suggests functional importance of and selective constraint on these developmental features. The relatively accelerated divisions of the 2d cell line in P. massiliensis may be interpreted as the precocious development of cell lines which give rise to adult structures. Several structures, obviously functional in developing P. dumerilii, have lost their function in P. massiliensis: the egg contains few cortical granules, giving rise to only a moderate egg jelly layer in the zygote; prototroch cells develop cilia, but the heavy embryo is unable to swim; the larva develops three pairs of parapodia but, unlike the corresponding stage in P. dumerilii, is not capable of coordinate locomotion. This loss of motility is related to the brooding habit of the species developing inside the parental tube and is explained as the result of a switch from pelagic to benthic, protected reproduction in P. massiliensis.
Offprint requests to: A.W.C. Dorresteijn 相似文献
66.
The antitumor potency of progesterone antagonists is due to their differentiation potential. 总被引:2,自引:0,他引:2
H Michna S Gehring W Kühnel Y Nishino M R Schneider 《The Journal of steroid biochemistry and molecular biology》1992,43(1-3):203-210
A new therapy for the progesterone receptor positive mammary carcinoma may be the treatment with progesterone antagonists. This new class of antihormones causes a strong inhibition of tumor growth comparable to the potency of ovariectomy in a panel of experimental mammary carcinomas. The mechanisms of the strong tumor-inhibiting action of progesterone antagonists on experimental mammary carcinomas mainly depends on a progesterone receptor mediated process leading to induction of terminal differentiation and a blockade of the cell cycle. To further characterize the antitumor mechanism of progesterone antagonists we analyzed the effects of Onapristone and ZK 112.993 on DMBA- and MNU-mammary tumors of the rat and MXT-tumors of the mouse after different therapy intervals. These hormone-dependent mammary tumors normally display intraductal growth in papillary, cribiform or solid formation, whereas after treatment periods of 2-6 weeks with progesterone antagonists they displayed dysplastic ductal and acinous formations, usually filled with secretory material. Whereas tumor size, mitotic index, and the grade of tumor malignancy decreased distinctly, the volume fraction of glandular structures in the tumors as well as the appearance of apoptosis increased 3-fold compared to the controls. In addition, the mammary glands of progesterone antagonist treated animals showed the morphological features of differentiation with the appearance of secretory activity. Interestingly, the staining pattern of some of the lectins used, especially UEA 1 binding pattern, fits to the concept of differentiation since recent studies revealed a higher degree of fucosylation only in benign lesions of human breast cancers. Therefore, these data underline the concept of a differentiation potential of progesterone antagonists on progesterone receptor positive mammary carcinomas. 相似文献
67.
The technique of Perturbed Angular Correlations of -rays has been used to study the rotational correlation times in aqueous solution of the peptides: oxytocin, glycyltryptophan, cholecystokinin and the glycopeptide ristocetin. These peptides were labelled with excited 111mCd through the covalent coupling of the metal chelator diethylenetriaminepentaacetic acid (DTPA) to the primary amines-of the peptides. The experimental correlation times are in good accordance with calculations based on the molecular weight. This indicates that the 111mCd-DTPA is rigidly bound to the molecules. In the case of ristocetin, the correlation time was measured at 2°C, 25°C and 38°C. These experiments show the expected linear dependence on the viscosity divided by temperature. The feasibility of determining rotational correlation times for peptides without lysines and with correlation times in the ns region is thus demonstrated. Also, the correlation time of 111mCd-DTPA coupled to the lysines of bovine serum albumin was determined. The measured correlation time is about 5 times less than the calculated correlation time. This effect is assigned to local motion. In spite of this, experiments show that 111mCd-DTPA-bovine-serum-albumin is significantly immobilised by aggregation with immunoglobulins. The nuclear quadrupole interactions, necessary for determining the correlations times, were determined for 111mCd-DTPA-ristocetin and 111mCd-DTPA-bovine-serum-albumin by adding sucrose to a concentration of 63% and cooling to 2°C. This showed a small but significant difference between the two molecules. We interpret this as due to different conformations, possibly different coordination numbers.
Offprint requests to: E. Danielsen 相似文献
68.
Prohibitin, an evolutionarily conserved intracellular protein that blocks DNA synthesis in normal fibroblasts and HeLa cells. 总被引:21,自引:7,他引:14
M J Nuell D A Stewart L Walker V Friedman C M Wood G A Owens J R Smith E L Schneider R Dell' Orco C K Lumpkin et al. 《Molecular and cellular biology》1991,11(3):1372-1381
Genes that act inside the cell to negatively regulate proliferation are of great interest because of their implications for such processes as development and cancer, but these genes have been difficult to clone. This report details the cloning and analysis of cDNA for prohibitin, a novel mammalian antiproliferative protein. Microinjection of synthetic prohibitin mRNA blocks entry into S phase in both normal fibroblasts and HeLa cells. Microinjection of an antisense oligonucleotide stimulates entry into S phase. By sequence comparison, the prohibitin gene appears to be the mammalian analog of Cc, a Drosophila gene that is vital for normal development. 相似文献
69.
70.
Protein and other compositional differences of the extracellular material from slimy and non-slimy colonies of non-mucoid Pseudomonas aeruginosa 总被引:1,自引:0,他引:1
The composition of extracellular material produced by non-mucoid strains of Pseudomonas aeruginosa differed when grown on surfaces that either did or did not induce the formation of slime under conditions where the medium was identical. The nature of the changes in protein composition indicated that protein expression differed in the course of growth on the two surfaces, and hence that there were physiological consequences associated with growth under conditions which do or do not lead to slime formation. The compositional differences also included elevated levels in extracellular material from the slimy colonies of two virulence factors, protease and rhamnolipids. 相似文献