Second Messenger:

The most commonly referred to second messengers are cyclic AMP and cyclic GMP.    After ATP binds to the P2Y series of receptors on cells, it leads to changes in these second messenger molecules.   The result activates or inactivates enzymes with in a cell.   The following links demonstrate what occurs when the levels of these molecules are changed:

http://www.youtube.com/watch?v=MF0EjhcpAos
http://www.youtube.com/watch?v=iGb93jCKVXs
http://www.youtube.com/watch?v=NMeBZlbs2dU&feature=autoplay&list=PL45ACD6ACF7339205&index=4&playnext=1

Additional Links:

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/S/Second_messengers.html
http://www.pearsonhighered.com/mathews/ch23/c23sms.htm
http://www.humpath.com/spip.php?article1420

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