Cell Signalling and Transduction
Which of the following is true about a hydrophilic signaling molecule?

Since it can enter the cell, it directly affects some specific cell process
It is a steroid
It might trigger a signal cascade that causes some effect in a cell
Its receptor is located in the cytosol of the target cell

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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

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

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Cell Signalling and Transduction
The signaling molecules called steroid hormones

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

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Cell Signalling and Transduction
In the signal transduction mechanism known as protein phosphorylation

phosphorylated proteins act with enzymes to trigger the signal cascade
the signaling molecule binds to a surface receptor
All of these
receptor kinases play a key role in triggering the signal cascade

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