Chapter 7 Signaling

Chapter 7 Signaling - Signals Cells in your body release...

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Signals Cells in your body release and receive chemical signals from the environment and from other cells. For example, they may send signals to themselves (autocrine), to local neighbors (paracrine), or to cells at a great distance (hormones). Some cells can receive other kinds of signals, like light or sound.
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Signal transduction The entire signaling process, from signal detection to final response, is called a signal transduction pathway. A signal transduction pathway involves a signal, a receptor, transduction, and effects. A signaling molecule that binds the receptor is called a ligand . Receptors bind ligands according to the law of mass action, and thus the binding is reversible. Binding of the ligand causes the receptor to change shape, and then the ligand has no further involvement in the pathway.
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Induction of the lac operon Bacteria can respond to their environment. For example, in the presence of the sugar lactose , they synthesize three proteins involved in lactose metabolism, including β -galactosidase. In the absence of lactose, bacteria make none of these proteins. The three contiguous structural genes and the nearby promotor and operator regions of DNA comprise the lac operon .
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Transcriptional regulation in bacteria The ‘lac repressor’ protein binds to the operator DNA and blocks transcription of the three genes. When the repressor binds lactose, it pops off the DNA and permits transcription.
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Regulation of gene expression in eukaryotes Transcriptional control (by transcription factors) is just the first of many mechanisms that regulate gene expression. For example, to produce messenger RNA (mRNA), parts (the exons) of the initial transcript (pre- mRNA) must be spliced together, and the splicing may vary with cell type. More examples: The transport of mRNA from the nucleus, its stability, and the rate of translation into protein are all under control. Moreover, after a protein is produced, it may be modified or broken down, all under control by other genes or signaling pathways.
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In order to respond to changes in osmotic pressure (omp), a high external solute concentration causes the EnvZ protein to change shape and act as a kinase to phosphorylate itself. It then transfers the phosphate to the OmpR protein, which changes shape and initiates transcription of the ompC gene. The newly produced OmpC protein inserts into and closes pores in the outer membrane, thus preventing additional solute from entering the intermembrane space. Signal.
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Chapter 7 Signaling - Signals Cells in your body release...

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