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The Cell


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     The cell is the basic unit of almost all living organisms (viruses and prions are not cells). There are a multitude of cell types, each performing a specific function. It takes about 75 billion cells to build a human body. The more we known about the functioning of the cell, the more we realize that it is as complex as a whole organism. The cell is a manufacture of life.

Representation of a  cell.
Representation of a cell.

DNA model.
DNA model.

    In the center of the cell you find the nucleus (shown in blue in the figure). The nucleus contains the genetic material, the DNA (deoxyribonucleic acid) which is primary used for the elaboration of proteins and enzymes necessary for the cell functioning. Only the template for protein building, the mRNA, is produced in the nucleus; the protein themselves are produced outside the nucleus, in the rough endoplasmic reticulum (shown in green near the nucleus). The energy required by the cell to withstand all these chemical reactions, is provided mostly by the sugar which is metabolized in the mitochondria (shown in pink). Finally, metabolic wastes and wasted proteins are degraded in lysosomes (shown in orange). All these organelles, bath in a saline solution (the cytoplasm) which is retained by the cell membrane (shown in beige).

   Each side of the membrane there is a gradient of elements between the extracellular and intracellular milieu. These elements, or at least some of them, can pass through pores that open and close, and change the 'metabolic' status of the cell. For example, an entry of NA+ will introduce positive charges inside the cell and generate a difference of potential between the extracellular and intracellular milieu, hence an electrical current.

Distribution of intra- and extracellular elements.
Distribution of elements between the intra- and extracellular milieu.

A nice web site about the cell:

A great video depicting some intracellular molecular processes:
Top of the page.      TEXT© 2000-2015 René St-Jacques