Cell theories

Interpretation of the process of fermentation by yeast was one of the most controversial issues for vitalists. Its resolution was fundamental for the future development of biochemistry. In the early nineteenth century fermentation was believed to be related to putrefaction and decay. Liebig considered it to result from the breakdown of a substance (sugar) following the admission of air to the nitrogenous components in yeast juices. After the must of grape juice had fermented, the liquid cleared and the yellow sediment, yeast, was deposited. 

Schwann, the cell theory emerged.. cells are organisms and entire animals and plants are aggregates of these organisms arranged according to definite laws (Schwann, 1838). 

By 1839 Schwann was distinguishing between the combination of molecules to form cells and those phenomena which resulted from chemical changes either in the component particles of the cell itself or in its surroundings. 

These may be called metabolic phenomena. [Metabolism] is an attribute of the cells themselves [with] vinous fermentation an instance of this. [Further,] each cell is not capable of producing chemical changes in every organic substance... but only in particular ones. The metabolic power of cells is arrested not only by powerful chemical action, [which] destroys organic substances in general, but also by matters which are chemically less uncongenial, [e.g.] concentrated solutions of neutral salts [or by] other substances in less quantity [e.g.] arsenic. 

Schwann was also vigorously anti-vitalist, being unable to accept the idea of a force whose properties changed with the organ under study, exhibiting contractility in muscle, excitability in nerves, etc. 

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Microscopists were not entirely idle, however, and after Giovanni Battista Amici (1786-1863) introduced achromatic lenses in France in 1827, the cell theory was not far behind. Henri Dutrochet (1776-1847) had already proposed that animal and plant tissues were constituted of cells, a view reiterated by many, notably Jan Evangelista Purkyne (1787-1869), Johannes Muller (1801 -1858), andjacob Henle (1809-1885). Felix Dujardin... 

Virchow, who was largely responsible for the acceptance of the cell theory, developed microscopy of cells from normal and diseased tissues as a major tool (histopathology) in the clinical armory. He believed the vital functions of the cell, growth, maintenance, and multiplication were discharged by its nucleus the specialised, distinguishing functions were made possible by the extranuclear constituents. In a Sunday evening lecture in Edinburgh in 1868, On the Physical Basis of Life , Thomas Huxley described cells as protoplasmic masses usually... 

The discovery of TNTs may end up challenging the established cell theory concept of a cell as the primary unit of life in animals, if future studies can reveal a role of TNT-mediated communication in fundamental cellular processes. In the plant kingdom the multicellular organism is already considered the primary unit of life, driven by the role of plasmodesmata, cytoplasmic channels interconnecting plant cells, in processes such as cellular differentiation and development (reviewed in Baluska et al. (2004)). 

Baluska F, Volkmann D, Barlow PW (2004) Eukaryotic cells and their cell bodies Cell theory revised. Ann. Bot. (Lond) 94 9-32. 

F. Barbir. PEM fuel cells—Theory and practice. Burlington, MA Elsevier/ Academic Press (2005). 

Barbir, F. 2005. PEM fuel cells Theory and practice, 99-112. Boston Elsevier/ Academic Press. 

Microarrays for Cancer Research Historical Perspectives Tumor Heterogeneity Stem Cell Theory of Cancer Profiling Small Samples with Microarrays Amplification... 

While natural heterogeneity of cancer specimens is well documented, and the ability to isolate hundreds to thousands of cells with techniques such as LCM have allowed microarray analysis of more pure populations, the recent re-introduction of the cancer stem cell theory (24,25) has presented an extreme example of the need to isolate rare populations of cells. Cancer stem cells appear to exist at a frequency on the order of 1 in 1000 cells (26). While obtaining completely pure populations of stem cells remains difficult, highly enriched populations of these cells can be isolated using flow cytometry separating on the basis of the presence of certain specific cell markers. 

Volume II, Embryonic and Adult Stem Cells, provides an analysis of various types of stem cells and their therapeutic potential. It concentrates particularly on embryonic and neural stem cells. This volume covers the broader potential of adult stem cells its biology, significance and potential for therapy. This volume also describes the potential of stem cells for autologous transplantation, the stem cell theory of carcinogenesis, particularly the existence of brain tumor stem cells, and the therapeutic potential of gene therapy for cell-based therapy. 

Scadden D.T. (2006) The stem-cell niche as an entity of action. Nature. 441, 1075-9. Trosko J.E., Chang C.C. (1989) Stem cell theory of carcinogenesis. Toxicol Lett. 49, 283-95. 

The concept of the cell, or cell theory, was developed by the middle of the nineteenth century when living structures had been observed with the microscopes which were then available. The theory stated that all living systems are composed... 

On the basis of the local-cell theory, an ultrapure metal without impurity inclusions would be expected to be incorrodible. In general, the purer a metal, the more stable it is in an aqueous environment. But even an ultrapure metal corrodes. 

Fig. 12.7. According to the local-cell theory, corrosion can take place if the piece of metal is in a moist atmosphere. There are separate sites for the deelectronation and electronation reactions.

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 ... 

Compartmentalization is one of these key functions. Compartmentalization is global in terran life forms, which are built from cells that span a wide range of sizes. Cellular structure is so widespread on Earth that a central theory in biology is known as cell theory. An unexpected form of life that would be considered weird would be a life form that does not exploit cells but achieves a distinction between self and non-self that is not cellular as we define the term. 

In 1852 Robert Remak explicitely rejected the free-formation idea and concluded that Cells always come from the division of other cells. In 1855 Rudolf Virchow reached the same conclusion by studying a great number of normal and pathological adult tissues, and condensed it with the motto omnis cellula e cellula . The final version of the cell theory is therefore the combination of Schleiden and Schwann s first theory with the conclusion of Remak and Virchow All living creatures are made of cells and of cell products, and cells are always generated by the division of other cells. ... 

With the advent of the cell theory, embryonic growth was immediately accounted for by a sequence of cell divisions. A fertilised egg becomes 2 cells, and then 4, 8, 16, 32, 64 and so on. With 10 divisions the cell number is about a thousand, with 20 is a million, with 30 is a billion, with 40 is a thousand billion, and so forth. For the... 

The great philosophers of antiquity discussed quite a number of world views, such as the atomic theory, determinism and indeterminism, relativity and evolution, and yet none of them conceived the cell theory, which makes us wonder why. The fact that they did not have the microscope does not seem to be decisive from a conceptual point of view. Even atoms cannot be seen, and yet the atomic theory was explicitely formulated. The problem is therefore the following Why could ancient people think about atoms but not about cells The idea that matter can be divided into particles is suggested by many facts of daily life a house is made of bricks, a desert is made of grains of sand, drops of rain can be turned into a river, and so on. Why not add that organisms are made of micro-organisms ... 

The first version is a mere acknowledgment that cells exist, at least on our planet. The second one states that cells are the fundamental components of all forms of life, including extraterrestrial and artificial life. It states that cells are the logical units of the living world, just as atoms are the units of the physical world. The strong version of the cell theory, in other words, declares that life does not exist without cells, and represents therefore a definition of life itself life is the state of activity of cells and of cellular systems. 

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