Signal transduction links

Optional reading:

Discovery of G proteins. The 1994 Nobel Prize was awarded to Gilman and Rodbell for discovering G proteins and the processes of signal transduction.  The "Press Release" describes their scientific findings, and there are neat illustrations and biographical notes.  

Figures from Becker, Kleinsmith, Hardin, The World of the Cell (4th edition, figure # differs from 3rd ed.):
Fig 10-4: The G protein activation/inactivation cycle
Fig 10-5: The structure and metabolism of cAMP
Fig 10-6: The role of G proteins and cyclic AMP in signal transduction
Fig 10-8: The role of DAG and IP3
Fig 10-9: The role of IP3 and DAG in signal transduction
Fig 10-11: An overview of calcium regulation in cells
Fig 10-16: The structure and activation of a receptor tyrosine kinase
Fig 21-27: Activation of gene transcription by glucocorticoid receptors

Animations(You'll need to download Shockwave to see some of these.)

Production of IP3 and Ca2+ Ion Wave. A really cool animation! You have to repeatedly hit the Go button for it to proceed to the next step.
Endocrine system . The mechanism of hormone actions includes an animation of tyrosine kinase receptor activation.
Dopamine receptor activation, with G protein
3-D model of G-protein-linked receptor