Eukaryotic Chemotaxis
The mechanism which eukaryotic cells employ is quite different from that in bacteria; however, sensing of chemical gradients is still a crucial step in the process. Due to their size, prokaryotes cannot detect effective concentration gradients, therefore these cells scan and evaluate their environment by a constant swimming (consecutive steps of straight swims and tumbles). In contrast to prokaryotes, the size of eukaryotic cells allows for the possibility of detecting gradients, which results in a dynamic and polarized distribution of receptors. Induction of these receptors by chemoattractants or chemorepellents results in migration towards or away from the chemotactic substance.
Levels of receptors, intracellular signalling pathways and the effector mechanisms all represent diverse, eukaryotic type components. In eukaryotic unicellular cells, ameboid movement and cilium or the eukaryotic flagellum are the main effectors (e.g. Amoeba or Tetrahymena). Some eukaryotic cells of higher vertebrate origin, such as immune cells also move to where they need to be. Besides immune competent cells (granulocyte, monocyte, lymphocyte) a large group of cells - considered previously to be fixed into tissues - are also motile in special physiological (e.g. mast cell, fibroblast, endothelial cells)or pathological conditions (e.g. metastases). Chemotaxis has high significance in the early phases of embryogenesis as development of germ layers is guided by gradients of signal molecules.
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