Cellular Biology

The cellular biology , or cytology , is a discipline of the Biologie studying the cell S and their Organite S, the vital processes which proceed there as well as the mechanisms allowing their survival (reproduction, Métabolisme, Homéostasie, Néguentropie, Communication) without forgetting the principal characteristic of the alive cell, namely, the Mort, which can be is programmed genetically (Apoptose) or being the result of an aggression (Nécrose).

The Histologie is as for it the study of the cells on a higher level, i.e. their fittings in fabric S and their interactions (simple cellular junctions, etc).

The study of the operation of the cell does not enter the field of cellular biology. It constitutes a separated field, cellular physiology.

History

It was difficult for people to imagine the existence of too small living organisms to be seen or to believe that they could carry reached to hosts of big size. In a general way, the existence of Micro-organism S.A. denied until in 1677 when they were seen and described by Antonie van Leeuwenhoek (1632 - 1723), a cloth merchant with Delft (Netherlands), which did not have any scientific formation but a great patience and a great curiosity. It succeeds in obtaining strong enlargements (300 ×) thanks to a microscope simple compound of only one small almost spherical lens. In its letters published by Royal The Society off London, it described a very new world, before invisible, including/understanding “animalcules” (recognized now like bacteria and protozoa) of which mobility showed that they were alive.

Cellular biology had been born with the invention from the optical first Microscope (photonic) by Antonie van Leeuwenhoek.

The study of the Micro-organism S (from which the Bactérie S) only with the development from a optical Microscope became really accessible made up (multilentilles) effective about the years 1825.

Rudolf Virchow (1821 - 1902), German physiologist is the author of the proverb “omni cellula E cellula”, or as it publishes it in 1858 in Cellularpathologie “Where a cell appears, it must have had another cell before” “Any animal appears there as the sum of vital units of which each one carries in it all the characters of the life. ”

The cell is thus a separate enclosure of outside by a membrane able to filter the exchanges selectively.

Until the 19th century, the living organisms were classified like animal or vegetable according to obvious differences of form and constitution, which décombent of basic differences in their mode of nutrition.

The animal nourish organic substances which are hydrolized and absorbed on the level of the intestinal tract inside the body. The development of the animals seems, indeed, to have for goal creation of absorbing internal large surfaces. This principle of construction applies to a great range of animals, since the hydrozoaires to the vertebrate superiors.

The Plante S are built on a completely different level. They synthesize the substances necessary for their growth and their maintenance starting from inorganic materials and use like energy source, solar light. The cells and fabrics photosynthétiquement active are thus directed towards outside and form external large surfaces. Other general differences between the plants (plants) and the animals are the presence of cellular walls, the capacity of active movements, change of position in the environment, the aptitudes to synthesize various substances, etc

This clear distinction between vegetable kingdoms and animal remained easy as a long time as nothing was known or almost micro-organisms. Even the Mushroom S superiors, in spite of their nutrition (they nourish organic matters like the animals) and in spite of the fact that they are deprived of chlorophyl, could be included in the vegetable kingdom, dividing many of other properties with the higher plants.

When it was necessary to attach the bacteria, mucous mushrooms or unicellular myxocètes and other organizations with one or the other of the two reigns, the decisions proved much more difficult. It was necessary to be solved to establish a third category of living organisms who received the collective name of Protistes (primary or antiquated forms of life) (Haëckel, 1866): the reign of the Protiste S contains the organizations which are different from the plants and the animals by the morphological absence of specialization, the majority of them being unicellular.

The protists were subdivided in two groups differentiated on basis from their cellular structure. Lower protists or Procaryotic S (of the Greek: primitive core) have a cellular structure different from that of all the other organizations: this group includes the Bactérie S, the Cyanobactérie S (blue algas) and the Rickettsie S (obliged intracellular parasites). Higher protists or Eucaryote S (of the Greek: true core) resemble the plants and the animals in their cellular structure: they are the Algue S, the lower Champignons and the Protozoaire S.

The general term of micro-organisms (studied by microbiology) comes only from the tiny size of the various organizations mentioned above. It corresponds in its significance and its application to that of the protists.

The Virus do not answer the definition of the protists although they are included in the great majority of the handbooks of microbiology. They are noncellular, unable particles of autoreplication and being able to proliferate only in certain alive cells. Their very small size (in general, lower than 250 nanometers) requires the use of a Electron microscope to visualize them as particulate objects.

Techniques used

Cellular biology uses many techniques to study cellular morphology. The technique queen remains however the Microscopie with all its alternatives. It is the Microscope which allowed its birth the 17th century and there remains always the principal means of studies. The microscope diversified today to improve visualization of the structures: since the optical microscope simple lens of the origins, one developed more complex optical microscopes using the direct light or fluorescence, as well as electron microscopes.

In parallel the techniques of Coloration developed allowing the description of increasingly fine structures and to better locate them within the cell. Thus, if the first colorings made it possible to currently visualize the general characteristics of the cellular zones (Acide S, basic, rich in Lipide S, etc), thanks to the use of the Anticorps and the Toxine S, one can detect the position of a precise Molécule and to a certain extent to proportion it or follow its temporal evolution. These techniques are not however specific to cytology and are also largely used in Histologie.

The majority of these techniques are lethal for the cell and the latter seldom survives coloring, especially for the most complex techniques. This is why the Contrasting phase microscope is largely employed considering that Ci makes it possible to observe alive cells.

External bonds

See a detailed diagram of the cell.
PubMed - Bookshelf - Online Books
Biology Concealment - School and University - Graphics

Simple: Cytology

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