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81.
82.
Protein synthesis is the final step of gene expression in all cells. In order to understand the regulation of this process,
it is important to have an accurate model that incorporates the regulatory steps. The model presented in this paper is composed
of set of differential equations which describe the dynamics of the initiation process and its control, as well as peptide
elongation, starting with the amino acids available for peptide creation. A novel approach for modeling the elongation process
permits useful prediction of protein production and consumption of energy and amino acids, as well as ribosome loading rate
and ribosome spacing on the mRNA.
An erratum to this article can be found at 相似文献
83.
Fanchang Zeng Xianlong Zhang Shuangxia Jin Lei Cheng Shaoguang Liang Lisong Hu Xiaoping Guo Yichun Nie Jinglin Cao 《Plant Cell, Tissue and Organ Culture》2007,90(1):63-70
We conducted a systematic assessment and comparative study on the biochemical and cellular characteristics of cultured cotton
cells during the entire process of somatic embryogenesis (SE). All staged cultures were widely investigated in this assay.
Cell and tissue ectogenesis manipulation combined with flow cytometry (FCM) was employed to cellular study during the whole
totipotency process of dedifferentiation and redifferentiation. We identified two phases of chromatin decondensation during
the dedifferentiation and redifferentiation. At the same time, sharp increase in the ratio of indoleacetic acid (IAA), isopentenyladenosine
group (iPAs) at the same stage of cell dedifferentiation and redifferentiation process serve as distinct biochemical maker
of dedifferentiation and SE initiation with the unique feature. Our results suggest the two phases of chromatin reorganization
associated with endogenous auxin/cytokinin dynamic activity may underlie dedifferentiation and redifferentiation during the
entire SE process in cotton. 相似文献
84.
Engen S 《Mathematical biosciences》2007,210(2):490-507
There is often large variation in traits across the species of a community. In particular, variation in life history traits affecting population dynamics is likely to affect the species abundance distribution. Applying a dynamic and heterogeneous species abundance model we study how differences in extinction time for species in a community act as a force changing the distribution of dynamic parameters across species. This process may generate communities that are more heterogeneous then the heterogeneity measured as the species enter the community. Analytical results for some versions of the lognormal and gamma species abundance model are given as exemplifications of this process, together with stochastic simulations demonstrating the temporal changes in number of species and community heterogeneity through time. 相似文献
85.
Simulating the effects of N availability, straw particle size and location in soil on C and N mineralization 总被引:2,自引:0,他引:2
Predicting the C and N mineralization of straw added to soil is important for forecasting subsequent soil N availability during
and between crop growth cycles. The decomposition module of the STICS model, parameterized under optimal conditions, was used
to predict straw decomposition in sub-optimal conditions, i.e. when contact between soil and residue was poor (due to large
size residues or surface placement) or when mineral N availability was restricted. The data used in the simulations were obtained
from published studies of effects of residue size, location and N availability on C and N mineralization from straw under
controlled laboratory conditions. We selected studies in which the dynamics of C and N mineralization were measured simultaneously.
The dynamics of straw mineralization could be well predicted by the model under optimal conditions with standard parameter
values as derived from measured C/N ratios of the residues, but not under sub-optimal conditions which required a new parameterization. A good fit could be obtained
on these treatments by a marked reduction in the rate constants of residue and microbial biomass decomposition and a marked
increase in the microbial biomass C/N ratio. Our results show the need to include in decomposition models routines for simulating effects of spatial heterogeneity
of residue distribution, different particle sizes and limiting N availability. 相似文献
86.
Reichert J Grasnick D Afonin S Buerck J Wadhwani P Ulrich AS 《European biophysics journal : EBJ》2007,36(4-5):405-413
It is generally assumed that fusogenic peptides would require a certain conformation, which triggers or participates in the
rate-determining step of membrane fusion. Previous structure analyses of the viral fusion peptide from gp41 of HIV-1 have
yielded contradictory results, showing either an α-helical or a β-stranded conformation under different conditions. To find
out whether either of these conformations is relevant in the actual fusion process, we have placed sterically demanding substitutions
into the fusion peptide FP23 to prevent or partially inhibit folding and self-assembly. A single substitution of either D- or L-CF3-phenylglycine was introduced in different positions of the sequence, and the capability of these peptide analogues to fuse
large unilamellar vesicles was monitored by lipid mixing and dynamic light scattering. If fusion proceeds via a β-stranded
oligomer, then the D- and L-epimers are expected to differ systematically in their activity, since the D-epimers should be unable to form β-structures due to sterical hindrance. If an α-helical conformation is relevant for fusion,
then the D-epimers would be slightly disfavoured compared to the L-forms, hence a small systematic difference in fusion activity should be observed. Interestingly, we find that (1) all D- and L-epimers are fusogenically active, though to different extents compared to the wild type, and – most importantly – (ii) there
is no systematic preference for either the D- or L-forms. We therefore suggest that a well-structured α-helical peptide conformation or a β-stranded oligomeric assembly can
be excluded as the rate-determining state. Instead, fusion appears to involve conformationally disordered peptides with a
pronounced structural plasticity.
Dedicated to Prof. K. Arnold on the occasion of this 65th birthday. 相似文献
87.
We used stochastic dynamic programming to investigate a spectacular migration strategy in the black brant Branta bernicla nigricans, a species of goose. Black brant migration is well suited for theoretical analysis since there are a number of existing strategies that easily can be compared. In early autumn, almost the entire population of the black brant gathers at Izembek Lagoon on the Alaska Peninsula to stage and refuel before the southward migration. There are at least three distinct strategies, with most geese making a spectacular direct migration more than 5000km across the Gulf of Alaska to their wintering grounds in southern Baja California or mainland Mexico. This is a potentially dangerous strategy since foraging is not possible during the overseas passage. Some individuals instead use shorter flights to make a detour along the coast, a longer route that all individuals use for northwards migration in spring. Since flight costs accelerate with increasing body mass, migration by short flights is energetically cheaper than long-distance flights. A small but increasing part of the population has recently begun to winter at Izembek. We investigated this migration under two different suppositions using a dynamic state variable model. First, if the geese are free to make a strategic choice, under what assumptions should they prefer direct migration and under what assumptions should they prefer detour migration/winter residency? Second, provided that the dominating direct migration strategy is optimal, what conditions will force the geese to go for detour migration/winter residency? In the second case the geese may try to follow an optimal direct migration strategy, but stochastic events may force them to choose a suboptimal policy. We also simulated possible effects of global warming. The model suggests that the fuel level at arrival in Izembek and fuel gain rates are key factors and that tail winds must have been reliable in the past, otherwise direct migration could not have evolved. It also suggests that a change to milder winters may promote an unexpectedly abrupt change from long-distance to short-distance migration or winter residency. Finally, it produced a number of predictions that might be testable in the field. 相似文献
88.
Popp D Yamamoto A Iwasa M Narita A Maeda K Maéda Y 《Biochemical and biophysical research communications》2007,354(1):109-114
Apoptosis is a highly conserved procedure of cell death and occurs under various stimuli, including oxidative stress. A small heat shock protein, alphaB-crystallin, is found to process resistance to apoptosis in some cells and tissues. But the mechanisms under this protective role are not fully understood. In the present study, we reported the early protective role of alphaB-crystallin against hydrogen peroxide-induced apoptosis in mice myogenic C(2)C(12) cells. alphaB-Crystallin interacted with p53, a proapoptotic protein, during cell apoptosis and such protein interaction mainly occurred in the cytoplasm of the cells, suggesting that the interaction of alphaB-crystallin with p53 might prevent the translocation of p53 from cytoplasm to mitochondria. Hence, this study provides a hint that alphaB-crystallin affects on p53 mitochondrial translocation during oxidative stress-induced apoptosis. 相似文献
89.
Leg movements of stick insects (Carausius morosus) making turns towards visual targets are examined in detail, and a dynamic model of this behaviour is proposed. Initial results
suggest that front legs shape most of the body trajectory, while the middle and hind legs just follow external forces (Rosano
H, Webb B, in The control of turning in real and simulated stick insects, vol. 4095, pp 145–156, 2006). However, some limitations
of this explanation and dissimilarities in the turning behaviour of the insect and the model were found. A second set of behavioural
experiments was made by blocking front tarsi to further investigate the active role of the other legs for the control of turning.
The results indicate that it is necessary to have different roles for each pair of legs to replicate insect behaviour. We
demonstrate that the rear legs actively rotate the body while the middle legs move sideways tangentially to the hind inner
leg. Furthermore, we show that on average the middle inner and hind outer leg contribute to turning while the middle outer
leg and hind inner leg oppose body rotation. These behavioural results are incorporated into a 3D dynamic robot simulation.
We show that the simulation can now replicate more precisely the turns made by the stick insect.
This work was supported by CONACYT México and the European Commission under project FP6-2003-IST2-004690 SPARK. 相似文献
90.
Mosaic cycles in agricultural landscapes of Northwest Europe 总被引:2,自引:0,他引:2
Michael Kleyer Robert Biedermann Klaus Henle Elisabeth Obermaier Hans-Joachim Poethke Peter Poschlod Boris Schrder Josef Settele Doris Vetterlein 《Basic and Applied Ecology》2007,8(4):295-309
Mosaic cycles were originally understood as cyclical regeneration phases in forests. In this review, we shall examine how far the concept can be extended towards cyclical mosaics of habitat quality in patterned landscapes as a special case of ‘dynamic landscapes’. We will concentrate on habitats and plants in European temperate agricultural landscapes and grasslands in particular. Mosaic cycles of habitat quality are characterised by spatiotemporal shifts between disturbance and secondary succession. We found evidence for mosaic cycles in traditional agricultural systems, modern crop farming, and in recent conservation management. The relevant disturbance parameters to describe land-use drivers of mosaic cycles are spatial extent, frequency, and magnitude (biomass loss). Land-use-related drivers are usually regular and deterministic in space and time, with the exception of year-round grazing by free-ranging large herbivores. Fluctuating soil resources such as water and nutrients in interaction with climate variability add a stochastic component to these (land-use-related) drivers. The proportion of deterministic and stochastic components and their autocorrelation in time and space divides purely deterministic mosaic cycles from purely stochastic dynamic landscapes. In a second part, we briefly review plant life-history traits that may facilitate survival of plants in mosaic cycles of habitat quality. Theoretical studies emphasise (i) dispersal functions for extinction and recolonisation processes of metapopulations, (ii) storage effects as a component of buffered population growth in response to temporal fluctuations of habitat quality, and (iii) competitive ability in metacommunities. We propose a simple scheme relating these functions to the temporal and spatial correlation of patterned landscapes. There are only a very limited number of field studies available that give some support for the proposed scheme. We provide perspectives for further research in this field. 相似文献