Because nonsteroid hormones are unable to pass through the cell membrane, a second messenger is needed.

Question

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Nonsteroid hormones bind to receptors on the cell membrane and activate a second messenger inside the cell to relay the signal and initiate a response. This is necessary because the hormone molecule itself is too large and hydrophilic to pass through the hydrophobic cell membrane. Examples of second messengers include cyclic AMP, calcium ions, and inositol triphosphate/diacylglycerol.

Because Nonsteroid Hormones Are Unable to Pass Through the Cell