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Signal Transduction, continued Transduction and response When signal transduction is blocked or defective, the effects are usually harmful to the cell. Example: Cholera Some bacteria excrete exotoxins that interfere with signal transduction pathways. The bacteria that causes cholera is an intestinal parasite. Cholera toxin modifies a G-protein so that its attached GTP cannot be hydrolyzed back into GDP. This results in prolonged activation of intestinal cells, which increases water efflux into the intestine. Example: Type II Diabetes Mellitus can result from reduced kinase activity in the RTK activated by insulin. Example: Nerve agents destroy an enzyme that degrades the neurotransmitter acetylcholine. The buildup of acetylcholine leads to muscle failure and ultimately results in respiratory failure. Sarin gas, as well as some insecticides, are nerve agents. Example: In the autoimmune disease Myasthenia gravis, acetylcholine receptors are damaged by antibodies, resulting in loss of muscle coordination. Signal Transduction: Transduction and Response Transduction • Needed to continue the message to the inside of the cell • Domino effect • Original signaling molecule is NOT passed along • Very often, proteins change shape due to phosphorylation Second messengers are also often used. Second Messengers • Small, NON-PROTEIN, water-soluble molecules or ions • Most common: cAMP and calcium ions – You will do more work with these on your own. Your Job: • WebQuest (cAMP, problems w/ pathways) • Response- notes