Cell

A cell (Cell Latin, diminutive of cellam, cell, small room) is the morphological and functional unit of all living things. In fact, the cell is the smallest element that can be considered alive. Thus, can be classified living organisms according to the number of cells that have: if you only have one, are called unicellular (such as protozoa or bacteria, microscopic organisms), if they have more, they are called multicellular. In the latter the number of cells varies from a few hundreds, and in some nematodes, hundreds of billions (1014), as in the case of human beings. The cells usually have a size of 10 microns and a mass of 1 ng, while cells are much larger.

The cell theory, proposed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, postulates that all organisms are composed of cells and all cells derived from other precedents. Thus, all vital functions emanating from the cellular machinery and the interaction between adjacent cells, in addition, possession of genetic information, the basis of heredity, in its DNA allows the transmission of it from generation to generation.

The appearance of the first living organism on Earth is usually associated with the birth of the first cell. While there are many hypotheses speculate how it happened, it usually describes the process started by the transformation of inorganic into organic molecules under appropriate environmental conditions, after that, those associated biomolecules leading to complex capable of self-replicating entities. There are possible fossil evidence of cellular structures in rocks dated to around 4 or 3.5 billion years (Ga giga-years.). Evidence of the presence of life based on deviations from isotopic ratios are above (Isua supracrustal belt, 3.85 Ga.).

There are two main types of cells: prokaryotes (cells comprising archaea and bacteria) and eukaryotes (traditionally divided into animal and plant, while also including fungi and protists, which also have cells with characteristic properties).

History and cellular theory

The first approaches to the study of cell emerged in the seventeenth century, following the development in the late sixteenth of the first microscopes. These allowed for numerous comments, which led in only two hundred years morfológicorelativamente acceptable knowledge. The following is a brief chronology of these discoveries:

1665: Robert Hooke published the results of his observations on plant tissues, such as cork, made with a microscope of 50 increases built by himself. The researcher was the first, seeing in those tissues that were repeated units in the form of cells of a honeycomb, christened as elements of repetition, "cells" (Latin for cell, cells). But Hooke could only watch as dead cells could not describe the structures inside.

Early 1670: Anton van Leeuwenhoek observed various eukaryotic cells (such as protozoa and spermatozoa) and prokaryotes (bacteria).

1745: John Needham described the presence of "animalcules"or "infusoria": it was single-celled organisms.

Illustration of the structure observed by Robert Hooke cork under a microscope and as published in Micrographia.

Early 1830: Theodor Schwann cell studied animal with Matthias Schleiden postulated that cells are the basic units in the formation of plants and animals, and are the foundation of the life process.

1831: Robert Brown described the cell nucleus.

1839: observed Purkinje cell cytoplasm.

1850: Rudolf Virchow postulated that all cells come from other cells.

1857: Kölliker identified the mitochondria.

1860: Pasteur conducted many studies on the metabolism of yeasts and asepsis.

1880: August Weismann found that the current cell and molecular structural similarity shared with cells from ancient times.

1931: Ernst Ruska construyó el primer microscopio electrónico de transmisión en la Universidad de Berlín. Cuatro años más tarde, obtuvo un poder de resolución doble a la del microscopio óptico.

1981: Lynn Margulis published her serial endosymbiosis hypothesis, which explains the origin of the eukaryotic cell.