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Chapter 11 - Chapter 11 Cell Communication Chapter 11 Cell...

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Chapter 11 - Cell Communication Chapter 11 Cell Communication Lecture Outline Overview: The Cellular Internet 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 universal mechanisms of cellular regulation involving the same small set of cell-signaling mechanisms. o The ubiquity of these mechanisms provides additional evidence for the evolutionary relatedness of all life. Cells most often communicate by chemical signals, although signals may take other forms. Concept 11.1 External signals are converted into responses within the cell What messages are passed from cell to cell? How do cells respond to these messages? We will first consider communication in microbes, to gain insight into the evolution of cell signaling. Cell signaling evolved early in the history of life. One topic of cell “conversation” is sex. Saccharomyces cerevisiae, the yeast of bread, wine, and beer, identifies potential mates by chemical signaling. o There are two sexes, a and ?, each of which secretes a specific signaling molecule, a factor and ? factor, respectively. o 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 undergo other cellular changes. The two cells fuse, or mate, to form an a/? cell containing the genes of both cells. The process by which a signal on a cell’s surface is converted into a specific cellular response is a series of steps called a signal-transduction pathway. o The molecular details of these pathways are strikingly similar in yeast and animal cells, even though their last common ancestor lived more than a billion years ago. o Signaling systems of bacteria and plants also share similarities. These similarities suggest that ancestral signaling molecules evolved long ago in prokaryotes and have since been adopted for new uses by single-celled eukaryotes and multicellular descendents. Communicating cells may be close together or far apart.
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Multicellular organisms release signaling molecules that target other cells. Cells may communicate by direct contact. o Both animals and plants have cell junctions that connect to the cytoplasm of adjacent cells. o Signaling substances dissolved in the cytosol can pass freely between adjacent cells. o Animal cells can communicate by direct contact between membrane-bound cell surface molecules. o Such cell-cell recognition is important to such processes as embryonic development and the immune response. In other cases, messenger molecules are secreted by the signaling cell.
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