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41.
Rixon FJ 《Cell host & microbe》2008,3(3):120-122
In tailed bacteriophages and herpesviruses, double-stranded DNA is packaged into a pre-existing protein shell, through a dedicated channel known as the portal. In a recent issue of Molecular Cell, Zheng et al. determined the structure of the bacteriophage P22 portal complex in pre- and postpackaging conformations, identifying structural changes that serve to retain the genome within the virus particle and prime it for injection into a new host. 相似文献
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Intestinal iron absorption during suckling in mammals 总被引:1,自引:0,他引:1
The maintenance of appropriate iron levels is important for mammalian health, particularly during the rapid growth period
following birth. Too little iron can lead to irreversible damage to the developing central nervous system and too much iron
at this point can have adverse long term consequences, possibly due to excessive free radical production. In order to maintain
iron levels, intestinal iron absorption is very efficient in young mammals, such that almost all of the iron in breast milk
is utilized. However this high level of absorption is unable to be down regulated in response to excess iron as it can be
in adults, implying that different regulatory processes are involved during suckling. Various mechanisms have been proposed
to explain this high absorption, including enhanced expression of the proteins involved in iron absorption in adults (particularly
DMT1 and ferroportin), non-specific uptake via pinocytosis, and the uptake of lactoferrin bound iron by the lactoferrin receptor.
However, at present the precise mechanism is unclear. It is possible that all of these components contribute to the high intestinal
iron absorption seen during suckling, or a novel, as yet undescribed, mechanism could be involved. This review summarises
the evidence for and against each of the mechanisms described above and highlights how little is known about iron homeostasis
in this vital stage of development. 相似文献
44.
Determination of regional ventilation and perfusion in the lung using xenon and computed tomography. 总被引:4,自引:0,他引:4
T C Kreck M A Krueger W A Altemeier S E Sinclair H T Robertson E D Shade J Hildebrandt W J Lamm D A Frazer N L Polissar M P Hlastala 《Journal of applied physiology》2001,91(4):1741-1749
We propose a model to measure both regional ventilation (V) and perfusion (Q) in which the regional radiodensity (RD) in the lung during xenon (Xe) washin is a function of regional V (increasing RD) and Q (decreasing RD). We studied five anesthetized, paralyzed, mechanically ventilated, supine sheep. Four 2.5-mm-thick computed tomography (CT) images were simultaneously acquired immediately cephalad to the diaphragm at end inspiration for each breath during 3 min of Xe breathing. Observed changes in RD during Xe washin were used to determine regional V and Q. For 16 mm(3), Q displayed more variance than V: the coefficient of variance of Q (CV(Q)) = 1.58 +/- 0.23, the CV of V (CV(V)) = 0.46 +/- 0.07, and the ratio of CV(Q) to CV(V) = 3.5 +/- 1.1. CV(Q) (1.21 +/- 0.37) and the ratio of CV(Q) to CV(V) (2.4 +/- 1.2) were smaller at 1,000-mm(3) scale, but CV(V) (0.53 +/- 0.09) was not. V/Q distributions also displayed scale dependence: log SD of V and log SD of Q were 0.79 +/- 0.05 and 0.85 +/- 0.10 for 16-mm(3) and 0.69 +/- 0.20 and 0.67 +/- 0.10 for 1,000-mm(3) regions of lung, respectively. V and Q measurements made with CT and Xe also demonstrate vertically oriented and isogravitational heterogeneity, which are described using other methodologies. Sequential images acquired by CT during Xe breathing can be used to determine both regional V and Q noninvasively with high spatial resolution. 相似文献
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Maya L. Groner Luke A. Rogers Andrew W. Bateman Brendan M. Connors L. Neil Frazer Sean C. Godwin Martin Krko?ek Mark A. Lewis Stephanie J. Peacock Erin E. Rees Crawford W. Revie Ulrike E. Schl?gel 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2016,371(1689)
Effective disease management can benefit from mathematical models that identify drivers of epidemiological change and guide decision-making. This is well illustrated in the host–parasite system of sea lice and salmon, which has been modelled extensively due to the economic costs associated with sea louse infections on salmon farms and the conservation concerns associated with sea louse infections on wild salmon. Consequently, a rich modelling literature devoted to sea louse and salmon epidemiology has been developed. We provide a synthesis of the mathematical and statistical models that have been used to study the epidemiology of sea lice and salmon. These studies span both conceptual and tactical models to quantify the effects of infections on host populations and communities, describe and predict patterns of transmission and dispersal, and guide evidence-based management of wild and farmed salmon. As aquaculture production continues to increase, advances made in modelling sea louse and salmon epidemiology should inform the sustainable management of marine resources. 相似文献
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