CellSignals211 - Cell Signaling and Communication 1 Just as...

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Cell Signaling and Communication - 1 Just as we communicate with other humans in a number of different ways, cells communicate with other cells and with their external environment with a set of cell signal mechanisms and process signal information in order to make appropriate responses within the cellular environment. Cellular communication is necessary to coordinate the myriad activities needed for any organism (unicellular or multicellular, prokaryote or eukaryote) to grow, develop and function. Most organisms use the same kinds of cell signaling mechanisms affirming again the uniformity of DNA for life processes. Cells typically use chemical signals for communication, but electromagnetic signals (light) and mechanical signals (pressure or touch) are not uncommon. Plants in particular respond to a host of external environmental signals. Nerve cells of animals are especially sensitive to stimuli (e.g., chemoreceptors, mechanoreceptors, photoreceptors, thermoreceptors, nocireceptors (pain), electroreceptors). However, cell-to-cell communication is most often chemical, and chemical communication within multicellular organisms, particularly in animals, is the focus of this section. To start our discussion, lets look at a few examples of cell signaling to give you an idea of what we mean: Cellular slime molds secrete chemicals that induce adjacent cells to aggregate into a multicellular "slug" when growth conditions are unfavorable. This slug can disassemble, migrate or form a resistant "fruiting body" depending on the conditions. Some myxobacteria aggregate to form a resistant colony, or fruiting body, when their nutrients are diminished. Nutrient deficient bacteria secrete a chemical into their environment that attracts others. Within the fruiting body, the cells produce thickened walls, forming resistant spores that withstand the poor environment. Myxobacteria Aggregating Fruiting Bodies Many protists and other unicellular organisms are similar in morphology. Gender is determined by genetic "mating types" and sexual reproduction requires individuals of different mating types to recognize each other in non-visual ways. Recognition is chemical. One individual recognizes an appropriate mate by secreting its chemical mating factor for which a compatible mate will have a receptor. The compatible mate will secrete its mating factor, for which the original cell has a receptor. These signals bind to the respective membrane receptors of the "mate" to trigger fusion of the two cells. Typically, once a zygote is formed, meiosis occurs and the new generation's haploid cells are formed. 50% will have one mating type, 50% the other.
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Cell Signaling and Communication - 2 Receptiveness to sexual reproduction is a common use of chemical signals. Female insects secrete pheromones that can be detected by males of the
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CellSignals211 - Cell Signaling and Communication 1 Just as...

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