Cell Signalling and Transduction
cAMP and cGMP are derived from

GTP and ATP by the actions of adenylate cyclase and guanylate cyclase respectively
ATP and GTP by the actions of adenylate cyclase and guanylate cyclase respectively
None of these
ATP and GTP by the actions of guanylate cyclase and adenylate cyclase respectively

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Cell Signalling and Transduction
A signal cascade induced by adrenaline or thyroxine

All of these
must begin with receipt of the signal molecule by a surface receptor
results in the activation of a sequence of enzymes needed for the cell effect
involves the activation of a G protein

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Cell Signalling and Transduction
The signaling molecules called steroid hormones

never enter the blood of humans
are made in one location of the body but have their effects some distance away
bind to cell surface receptors to trigger chemical cascades
are hydrophilic and so cannot penetrate the plasma membrane

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