The theoretical aspects of biochemical fuel cells

Biological systems can be used in three types of fuel cell: depolarization (or concentration) cell, product cell, and redox cell. The possibilities and theoretical limitations of each type of cell have been considered in terms of the metabolic activities of microorganisms and the coupling of these to electrochemical systems. The use of cell extracts and enzymes, particularly in an insoluble form, has been discussed.     

Geometric and functional constraints on bivalve shell morphology

The range of shell morphologies available to bivalves is constrained by the geometric properties of coiled shells, and by two contrasting functional necessities: positioning the umbones at a distance from each other, to allow an adequate amount of shell gape, and limiting linear growth of the axial shell margin, in order to prevent the ligament from being rapidly stretched beyond its elasticity limits. These necessities are achieved, or circumvented, in one or more of the following ways: (1) evolving a range of inequivalve adaptations, (2) allowing a large amount of interumbonal growth, while simultaneously adopting a ligament that quickly breaks and is continuously replaced during ontogeny, (3) adopting an outward curving ligament which flexes along its entire width, thus effectively placing the actual pivoting axis of the valves dorsally to the axial shell margin, (4) substituting the ligament with diductor muscles, (5) stopping growth before shell coiling reaches half whorl, (6) decreasing the whorl expansion rate throughout ontogeny, (7) orienting the coiling axes of the umbones at an angle to each other and to the hinge axis.     

Biological aspects of chronic lymphoid leukemia

The present study is concerned with clinical prognostic classifications of chronic lymphocytic leukemia derived from numerous statistics and multivariate survival analysis. We analyse the prognostic significance of some biological patterns: bone marrow histological studies, lymph node biopsies, size, structure and doubling time of blood lymphocytes, tumoral markers and karyotype analysis. The problem of the monoclonal clone origin is discussed: differentiation abnormality or proliferation of a physiological clone.     

Biological aspects of ceramide-enriched membrane domains

Ceramide has been shown to be critically involved in many aspects of cellular responses to receptor-dependent and -independent stimuli. For instance, ceramide was demonstrated to be a central component of the signaling cascades mediating apoptosis after death receptor stimulation, treatment with chemotherapy or exposure to gamma-irradiation or UV-A light. Further studies indicated the importance of ceramide for the infection of mammalian cells with bacterial, viral and parasitic pathogens. Ceramide is released by the activity of acid, neutral or alkaline sphingomyelinases or de novo synthesized. A concept unifying the diverse biological functions of ceramide indicates that ceramide forms distinct membrane domains, named ceramide-enriched membrane domains or platforms. These domains serve the clustering of receptor molecules, the re-organization of signaling proteins, the exclusion of inhibitory signals and, thus, initiate and greatly amplify a primary signal. In addition, ceramide directly interacts with and stimulates intracellular enzymes that may act together with signals initiated in ceramide-enriched membrane domains to transmit signals into a cell.     

Rate-of-dialysis technique: theoretical and practical aspects

In the rate-of-dialysis technique, chemical equilibrium exists throughout the experiment between the contents of the two halves of a dialysis cell. Initially, however, a trace amount of labeled dialysand is present in one of the half-cells, and the dialysis of that is followed as a function of time. The method is able to reveal whether a compound is stable under the conditions used or whether it is affected, for example, by aggregation, precipitation, oxidation, or hydrolysis. The rate constants for six inorganic ions and 22 organic molecules were determined, and no simple relations were found between rate constants and functions of molar masses. However, in two homologous series of compounds, a linear relationship between rate constant and molar mass was found, allowing for a preliminary identification of an unknown substance. Whether the presence of a macromolecule results in binding of the dialysand is easily tested for because in that case its rate constant is sharply diminished. High-affinity binding was studied using octanoate and laurate as ligands and human serum albumin as binding protein. The primary binding constants determined were similar to those obtained by equilibrium dialysis. However, the rate-of-dialysis technique is much faster, and its results are less scattered. The technique is well suited for binding studies performed with high protein concentrations because it is not affected by any osmosis or Donnan effects.     

Functional inference from gastropod shell morphology - some caveats

The dangers of making broad paleobiological inferences from shell morphology, based on limited observations of a few taxa, are indicated using as examples the secondary protoconchs of Colina species (Cerithiidae), and the ratchet sculpture of some surface dwelling species of Cerithium. Secondary protoconchs are not indicative of types of development and ratchet sculpture does not always indicate burrowing. □ Protoconch, shell morphology, functional morphology, burrowing, Cerithiidae.     

Biological aspects of reactive nitrogen species.

Nitric oxide (NO) plays an important role as a cell-signalling molecule, anti-infective agent and, as most recently recognised, an antioxidant. The metabolic fate of NO gives rise to a further series of compounds, collectively known as the reactive nitrogen species (RNS), which possess their own unique characteristics. In this review we discuss this emerging aspect of the NO field in the context of the formation of the RNS and what is known about their effects on biological systems. While much of the insight into the RNS has been gained from the extensive chemical characterisation of these species, to reveal biological consequences this approach must be complemented by direct measures of physiological function. Although we do not know the consequences of many of the dominant chemical reactions of RNS an intriguing aspect is now emerging. This review will illustrate how, when specificity and amplification through cell signalling mechanisms are taken into account, the less significant reactions, in terms of yield or rates, can explain many of the biological responses of exposure of cells or physiological systems to RNS.     

Ultrastructural morphology of the shell and shell membrane of eggs of common snapping turtles (Chelydra serpentina)

Common snapping turtles (Chelydra serpentina) lay nearly spherical, flexible-shelled eggs having an outer mineral layer composed of calcium carbonate in the aragonite form. The mineral layer is arranged into loosely organized groups of nodular shell units, with numerous spaces (or pores) between adjacent shell units. Shell units are structurally complex, consisting of an inner tip that is morphologically distinct from the main body of the shell unit. Contained within an intact shell unit at the interface of the tip and the main part of the shell unit is the central plaque, an apparent modification of the shell membrane that may serve to nucleate calcification of shell units during shell formation. The tips of shell units are firmly attached to a single, multilayered shell membrane throughout much of incubation. The calcareous layer begins to detach from the shell membrane about half-way through incubation, and changes in shell morphology attending this detachment indicate that snapping turtles may use the shell as a source of calcium during embryogenesis. The arrangement of the mineral layer into groups of shell units, the large number of spaces between shell units, and little or no interlocking of crystallites of adjacent shell units apparently are factors contributing to the ability of these eggs to swell as they absorb water.