Cours : Introduction to Cellular biology
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Cellular biology or cytology, is the science that studies the structural and functional units common to the organization of all living beings. A cell is the basic unit of all living beings, it is the smallest portion of living matter that can isolate and reproduce.
The first organisms were seen and described by Antonie van Leeuwenhoek (1632 - 1723), a cloth merchant of the Netherlands. This is probably exercising his profession that seeks to improve the magnifying power of magnifying glasses, he created a simple microscope obtaining high magnification (300 ×), and he invented the first optical microscope (or light microscope), observing all whatever came to hand, cell biology was born.
Today, various observation techniques used to study cells. A morphological study, using:
- The optical microscopy (or photon), which allows magnifications of the order of 2000 times
- The EM allows larger magnifications of the order of 200 times 000 000-2000
A study of functional and physico-chemical constitution:
- cytochemical study : fixing the cell, use of dyes with different affinities with the chemicals according to their pH (eg, DNA in green, pink RNA) using of antigen-antibody reactions and immune complex revealed by a dye and visualization under a light microscope.
- Cell Fractionation : grinding and centrifugation to isolate different populations of organelles and biochemical study of the different organelles.
- in-vitro culture : allows the study of cells under various conditions.
- Micro-Surgery : allows the removal or transplantation of organelles (study of the functions of organelles).
- Autoradiography : radioactive precursor (ie detachable) incorporated by cells and detected by radiography.
- Kinetics of the structure marked by sampling the time series in
These techniques allowed to distinguish two major cell types (two "empires"):
- Cells eukaryotes (with at least one core)
- Cells prokaryotes (no nucleus)
Prokaryotes can be divided into two groups the eubacteria and Archaea . The work of Woese in 75 years have allowed the definition in 1977 in the field of archaebacteria (or Archaea) following observations based on comparisons of 16S RNA and thus a division the world living in three areas: eubacteria, archaea and eukaryotes.
These are cells without a nucleus, small size and without intracellular organelles. Cytoplasm contains a region of the bacterial chromosome (warning, some eubacteria contain multiple chromosomes, which are not always circular): the nucleoid is not delimited by an envelope, he bathes in the cytoplasm. They may also contain various pieces of DNA but also circular and much smaller numbers vary (even between individuals of the same species or at different times in the life of one individual), the plasmids. Finally, these cells do not contain cytoskeleton.
For a long time was synonymous with prokaryotic bacteria, to the separation of eubacteria (true bacteria) and archaea. They share with eubacteria possession of a single circular chromosome, the absence of cytoskeleton, and very few introns. They have original features, including their membrane consists of lipids found nowhere else in the living world. The main feature of Archaea is their ability to survive in extreme environments: water very acidic (pH <1) or very salty (Dead Sea) or hot (> 120 ° C) or cold (<0 ° C), although that most of them live in warmer environments.
Eukaryotes are cells that make up the majority of the environment we conaissons, like all plants, animals and fungi as well as various species such as the unicellular amoeba or paramecium. They are characterized by the presence of organelles, intracellular kinds of organs. Among them, an organelle is always present: the nucleus, which contains the genetic information of the cell. The genetic structure of these cells consists of several linear strands of DNA (chromosomes) and the genes in "mosaic", meaning that the gene coding areas are cut into pieces (exons) that are separated by noncoding regions (introns). They are often large. They will develop a cytoskeleton, a sort of mobile intracellular structure that will allow both to stiffen (and compensate for their brittleness) and deform in a controlled manner, a phenomenon that is causing the movement of animals, but also phagocytic cells and is therefore directly responsible for the wide variety of animal forms that exist.
Thank you to Alain BERNOT (research professor) for his contribution to the development of this page.
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