Cell Signalling and Transduction
The signaling molecules called steroid hormones

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

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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

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

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

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

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