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What is the primary purpose of secondary messenger systems? In other words, what can a secondary messenger do in the body that a first messenger cannot?
The primary ability of secondary messengers is their ability to leave the cell membrane and travel through the phospholipid bilayer by being selectively hydrophilic or -phobic, allowing egress. This enables, for example, a cascade effect that greatly amplifies the strength of the original primary messenger signal.
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Which of the following is NOT an example of a second messenger?
Second messengers are intracellular signaling molecules. Epinephrine is a hormone that is released into the bloodstream and is thus never inside the cell. cAMP, Ca2+ and IP3 are all examples of second messengers. They respond to primary messengers—which are often hormones—by amplifying their effects and/or turning on downstream effectors.
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Which of the following is NOT an example of a second messenger molecule?
All of the examples listed are considered second messengers except for protein kinase C, which interacts with second messenger pathways as an effector; however, it is not a second messenger itself.
Recall that second messengers are used to amplify signals within the cell. A ligand may bind to a receptor on the cell surface in order to activate a signaling cascade. Second messagers will help propagate this cascade throughout the cytosol. The messengers essentially help transfer the signal from the receptor on the cell membrane to the proteins in the cytosol that will ultimately be affected.
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Second messenger cascades can be triggered by the binding of an extracellular ligand to a membrane-spanning G-protein coupled receptor (GPCR).
Which of the following best describes what happens to the GPCR after a ligand has bound to it?
G-protein coupled receptors begin the signal transduction pathway by interacting with intracellular G-proteins. This interaction isn't possible until a ligand forces a conformational change in the GPCR, thereby freeing up a site for the G-protein to bind. This interaction permits the G-protein to exchange a GDP for a GTP, thereby activating the G-protein and continuing signal transduction.
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Which of the following is NOT a primary benefit of utilizing second messengers to transduce signals within a cell?
The ligand binds the receptor on its extracellular terminus; therefore the ligand itself never enters the cell or passes through the membrane. Second messengers let the cell 'know' what is happening on the outside, but these extracellular molecules do not directly enter the cell.
All of the other answers describe benefits of the second messenger system.
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