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  • GPCRs, as you know,

  • Have a G-protein in tow.

  • Alpha, beta, gamma, sit

  • Waiting till the signals hit.

  • When receptors signals bind,

  • G-proteins respond in kind,

  • Swapping out their GDP

  • For triphosphate, gleefully.

  • Alpha, with its GTP,

  • Leaves, all full of energy.

  • A cyclase it will activate

  • That acts upon adenylate.

  • Cyclic AMPs then find

  • A PKA that they can bind.

  • With binding of cAMPs

  • R subunits part from Cs.

  • C subunits, floating free,

  • Are on a phosphate adding spree.

  • PKA phosphorylates,

  • And target proteins activates.

  • Another enzyme, PLC,

  • Awaits an alpha-GTP

  • To activate it, so it splits

  • PIP2 and makes two bits.

  • IP3 and DAG

  • Are second messengers, you see.

  • They work together as a team,

  • They've got a cunning little scheme.

  • IP3, at ion gates

  • On ER membranes, lets a spate

  • Of calcium into cytosol

  • That's bad enough, but that's not all.

  • The calcium binds a PKC,

  • And with the help of DAG,

  • The kinase it can activate

  • Proteins to phosphorylate.

  • The binding of a signal small

  • To GPCRs caused this all.

  • Transducing pathways work a spell

  • And change the actions of a cell.