Whether a molecule acts as a neurotransmitter or a hormone, which statement about physiological regulation by these molecules is false?
Correct answer: D. Second messengers will always be involved in the response of the target cell
- A. Target cells must have specific receptor proteins with which these molecules combine
- B. When these molecules bind to target cells, specific sequences of changes must occur
- C. There must be an 'off-switch' that will stop the induced changes
- D. Second messengers will always be involved in the response of the target cell
Explanation
This statement is false because not all hormones and neurotransmitters utilize second messengers. Steroid hormones (like testosterone and estrogen) and thyroid hormones are lipid-soluble, allowing them to pass directly through the cell membrane and bind to intracellular receptors in the cytoplasm or nucleus, directly influencing gene expression without needing a second messenger. Conversely, protein/peptide hormones and most neurotransmitters are water-soluble and must bind to surface receptors, which then typically trigger a second messenger cascade inside the cell to transmit the signal.
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About Chemical Coordination and Hormones
Chemical coordination uses hormones released by endocrine glands and carried in blood to specific target cells. Coverage includes the pituitary, thyroid, pancreas, adrenal glands, ovaries and testes, feedback control, and the contrast between slower, longer-lasting hormonal responses and rapid nervous coordination.
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