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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Cell Signalling and Transduction
Self-phosphorylation is an excellent mechanism for triggering specific catalytic function of the proteins involved in signal cascades because it

changes the shape and thus the enzymatic activity of the proteins involved
makes the receptor more likely to capture the signaling, molecule
None of these
allows hydrophilic signaling molecules to cross the plasma membrane

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Cell Signalling and Transduction
Why is it that inhaling nitric oxide reduces blood pressure only in the lung tissue and not elsewhere in the body*?

Because nitric oxide breaks down quickly and thus cannot travel far
Because other body tissues use a different signaling molecule
None of these
Because nitric oxide cannot cross cell membranes and enter the blood

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