Cell theory, origins

The cell theory of life was finally put forward in the early nineteenth century by Matthias Schleiden and Theodor Schwann. Schleiden worked primarily with plant tissue he argued for the central importance of a dark spot—the nucleus—within all cells. Schwann concentrated on animal tissue, in which it was harder to see cells. Nonetheless he discerned that animals were similar to plants in their cellular structure. Schwann concluded that cells or the secretions of cells compose the entire bodies of animals and plants, and that in some way the cells are individual units with a life of their own. He wrote that the question as to the fundamental power of organized bodies resolves itself into that of individual cells. As Schleiden added, Thus the primary question is, what is the origin of this peculiar little organism, the cell ... 

Recently an approach to obtain the entropy of water If om the well-known cell theory of liquids has been developed by Henchman [13] and provides not only quantitative accuracy but also valuable insight into the origin of the entropy of liquid water. We shall briefly discuss the theory in the following. 

Plant cell culture originating from Cell Totipotency Theory was proposed by Haberlandt, a German botanist, in 1902. Plant cell secondary metabolites are widely used, have significant economic value, and can be made into medicines such as paclitaxel, ginsenosides, and artemisinin. The structures of... 

The decisive advantage of the original Elory-Huggins theory [1] lies in its simplicity and in its ability to reproduce some central features of polymer-containing mixtures qualitatively, in spite of several unrealistic assumptions. The main drawbacks are in the incapacity of this approach to model reality in a quantitative manner and in the lack of theoretical explanations for some well-established experimental observations. Numerous attempts have therefore been made to extend and to modify the Elory-Huggins theory. Some of the more widely used approaches are the different varieties of the lattice fluid and hole theories [2], the mean field lattice gas model [3], the Sanchez-Lacombe theory [4], the cell theory [5], different perturbation theories [6], the statistical-associating-fluid-theory [7] (SAET), the perturbed-hard-sphere chain theory [8], the UNIEAC model [9], and the UNIQUAC [10] model. More comprehensive reviews of the past achievements in this area and of the applicability of the different approaches are presented in the literature [11, 12]. 

A common thread in all these applications is the need to understand what makes clathrate hydrates stable. This chapter will present some of the evidence that recent computer simulations have contributed to this issue. To provide a context for the simulation results, we begin with a brief description of clathrate hydrates and their experimental properties. This will be followed in Section 3 by a discussion of the current theory of hydrate stability (the cell theory). It is intended that this Section should bring out the main ideas behind the cell theory, as it is these basic principles that have motivated recent simulations for a rigorous derivation of the cell theory the reader is referred to the original work of van der Waals and Platteeuw [2]. The role of computer simulations in elucidating the behaviour of clathrate hydrates will be considered in detail in Section 4. 

In the next section, we summarize the key observations and theories regarding the operating mechanisms of Li-02 cells. Possible origins of these performance limitations are also described. It is important to keep in mind that different mechanisms may dominate under different operating conditions. For example, it has been shown that the current density [23], positive electrode material/architecture [32, 33], and system cleanliness [34—36] can play a significant role in the reaction mechanisms. 

The calculations were performed in the framework of a one-step model of photoe-mission derived from the one originally formulated by Pendry [1]. Nowadays the model includes relativistic effects [2-5], the possibility of having several atoms per unit cell [6], different types of layers and a realistic model for the surface potential [7]. It is further possible to consider ov erlayers on a surface. We will not review the theory here, which has been done already in several publications [2,4,6,8], but instead concentrate on the results. 

DNA has two broad functions replication and expression. First, DNA must be able to replicate itself so that the information coded into its primary structure is transmitted faithfully to progeny cells. Second, this information must be expressed in some useful way. The method for this expression is through RNA intermediaries, which in turn act as templates for the synthesis of every protein in the body. The relationships of DNA to RNA and to protein are often expressed in a graphic syllogism called the central dogma. The concept was proposed by Crick in 1958 and was revised in 1970 to accommodate the discovery of the RNA-dependent DNA polymerase. Crick s original theory suggested that the flow of information was always from RNA to protein and could not be reversed, yet it allowed for the possibility of DNA synthesis from RNA. 

At around this time, there was much scientific debate about the theory of the origin of species proposed by Charles Darwin (1809-1882), a theory which was to change the world. Darwin himself was very cautious about making statements on biogenesis. It was still too early to answer such questions, because neither results from the science of cell biology nor an extensive knowledge of our planet, the solar system and the cosmos were available. 

One of the original concepts governing oral absorption of organic molecules is the pH partition hypothesis . This hypothesis states that only the nonionized form of the drug is able to permeate the membranes of epithelial cells lining the GI tract [26], According to the classical pH-partition theory, permeability is expected to correlate not with the intrinsic partition coefficient but with the so-called distribution coefficient D of the solute [27], where D is defined as ... 

Recent development of mitochondrial theory of aging is so-called reductive hotspot hypothesis. De Grey [465] proposed that the cells with suppressed oxidative phosphorylation survive by reducing dioxygen at the plasma membrane rather than at the mitochondrial inner membrane. Plasma membrane redox system is apparently an origin of the conversion of superoxide into hydroxyl and peroxyl radicals and LDL oxidation. Morre et al. [466] suggested that plasma membrane oxidoreductase links the accumulation of lesions in mitochondrial DNA to the formation of reactive oxygen species on the cell surface. 

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