topic 8

topic 8 - Emily Lin 3/29/11 Topic 8: F 8.3, F 11.3-11.4, F...

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Emily Lin 3/29/11 Long distance cell communication is completed by intracellular signals through hormones, which carries information from a cell and acts on a target cell far away from the original cell. These are small molecules present in minute amounts, but can have large impact on the activity of target cells and the body as a whole. Hormones can either be lipid soluble or not. Those that are can diffuse across the plasma membrane into the cytoplasm whereas hydrophilic hormones do not. Long distance signaling coordinates the activities of cells throughout a multi-cellular organism by specific signal receptors. These are proteins that change conformation after binding to a signaling molecule. Most are located outside of the cell since most hormones aren’t lipid soluble. Receptors are dynamic and also can be blocked. When lipid soluble hormones bind to receptors inside the cell, they trigger a change in the cell’s activity directly, whether it is activating or shutting down genes, etc. Hormones that can’t diffuse across the membrane’s effects aren’t so direct, and needs to go through signal transduction, which changes extracellular to intracellular, to get transmitted. For example, G proteins, proteins that bind guanosine triphosphate, work by triggering the production of an intracellular (or second) messenger. Enzyme linked receptors work by triggering the activation of a series of proteins inside the cell through the addition of phosphate groups. Second messengers can then trigger protein kinases, or enzymes that activate/inactivate by adding a phosphate group to them. Second messengers aren’t restricted to a single role or single cell type and it’s common for more than one to be involved in triggering a cell’s response. There are also enzyme-linked receptors, like receptor tyrosine kinases (RTKs). When a hormone binds to RTK, the protein forms a dimer and has a binding site for P, which activates RTK. Then a bridge is formed between RTK and the protein Ras, which functions like a G protein, and they go through a phosphorylation cascade, which amplifies the original signal and either activate or deactivate a particular target protein that’s already in the cell. For signal deactivation, G proteins turn GTP back to GDP and phosphatases stop phosphorylation
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This note was uploaded on 03/04/2012 for the course BIO 142 taught by Professor Escabar during the Spring '08 term at Emory.

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topic 8 - Emily Lin 3/29/11 Topic 8: F 8.3, F 11.3-11.4, F...

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