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Chapter 11 - CHAPTER 11 CELL COMMUNICATION Introduction...

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CHAPTER 11 - CELL COMMUNICATION Introduction Cell-to-cell communication is absolutely essential for multicellular organisms. Cells must communicate to coordinate their activities. Communication between cells is also important for many unicellular organisms. Biologists have discovered some universal mechanisms of cellular regulation, involving the same small set of cell-signaling mechanisms. Cells may receive a variety of signals, chemical signals, electromagnetic signals, and mechanical signals. A. An Overview of Cell Signaling 1. Cell signaling evolved early in the history of life One topic of cell “conversation” is sex. The yeast Saccharomyces cerevisiae , the yeast of bread, wine, and beer, identifies its mates by chemical signaling. There are two sexes, a and α , each of which secretes a specific signaling molecule, a factor and α factor respectively. These factors each bind to receptor proteins on the other mating type. Once the mating factors have bound to the receptors, the two cells grow toward each other and experience other cellular changes. Two opposite cells fuse, or mate. The a / α cell contains the genes of both cells. The process by which a signal on a cell’s surface is converted into a specific cellular response consists of a series of steps called a signal-transduction pathway . The molecular details in both yeast and animal cells are strikingly similar, even though their last common ancestor was over a billion years ago. Signaling molecules evolved first in ancient prokaryotes and were then adopted for new uses by single-celled eukaryotes and multicellular descendents. Cell signaling has remained important in the microbial world. Myxobacteria, soil-dwelling bacteria, use chemical signals to communicate nutrient availability. When food is scarce, cells secrete a signal to other cells leading them to aggregate and form thick-walled spores.
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2. Communicating cells may be close together or far apart Multicellular organisms also release signaling molecules that target other cells. Some transmitting cells release local regulators that influence cells in the local vicinity. Paracrine signaling occurs when numerous cells can simultaneously receive and respond to growth factors produced by a single cell in their vicinity. In synaptic signaling, a nerve cell produces a neurotransmitter that diffuses to a single cell that is almost touching the sender. An electrical signal passing along the nerve cell triggers secretion of the neurotransmitter into the synapse. Nerve signals can travel along a series of nerve cells without unwanted responses from other cells. Plants and animals use hormones to signal at greater distances. In animals, specialized endocrine cells release hormones into the circulatory system, by which they travel to target cells in other parts of the body.
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