Dr. M said:
I don't know if this analogy/writing was yours or someone else's, and I'm not here to start a flame war. I just want to get that out in the open RIGHT NOW. This is NOT intended to start a riot on the boards.
Cyclic AMP is synthesized inside the cell; it doesn't cross the cell membrane at any time under normal physiological conditions. Cyclic AMP is a second messenger seen in cases of adrenergic, insulinic, and various peptide hormone signalling pathways. It is synthesized via adenylate cyclase, which resides on the inner membrane surface due to its hydrophobic lipid tail. Adenylate cyclase is activated by a variety of G-proteins, which (very briefly) are activated by receptor conformation/phosphorylation state changes due to external receptor substrate binding.
cAMP is NOT seen in steroid signalling, or if it is, this is not because of the integral membrane receptor/G protein pathway.
The reason for this is that in peptide/integral membrane receptor signalling the first messenger (hormone) cannot cross the cell membrane. Steroids are lipid-soluble, and easily cross the lipid bilayer to enter the cell. Once there, they can diffuse to the nucleus and act on the sterol regulatory elements and various transcriptional promoters which induce an anabolic state in a variety of ways.
The transcriptional activation produces mRNA (messenger RNA) which encodes for various proteins, and these mRNAs are translated by ribosomes. There is no direct effect of the steroid itself on the ribosome; ribosome activity is governed by assembly/disassembly which is mediated by mRNA levels in the cell, although your statement that ribosomes are stimulated to increase protein synthesis is ultimately correct (even though your proposed mechanism of activation is not).
-M