Difficulty: Easy
Correct Answer: Presence of a specific hormone receptor on or in the cell
Explanation:
Introduction / Context:
Hormones are chemical messengers that travel through the blood and coordinate activities in different parts of the body. However, not every cell responds to every hormone. Only certain target cells change their behaviour when a hormone is present. This question tests whether you understand that the key feature that makes a cell a target for a specific hormone is the presence of the matching receptor, either on the cell surface or inside the cell, rather than the mere presence of the hormone in the blood.
Given Data / Assumptions:
Concept / Approach:
A hormone can only affect a cell if that cell has the appropriate receptor that can bind the hormone. These receptors are proteins located either on the cell surface (for peptides and many amine hormones) or inside the cell (for steroid and some thyroid hormones). When the hormone binds to its receptor, it triggers a signal transduction pathway that changes the cell activity. A hormone response element is a specific DNA sequence in the nucleus that certain hormone receptor complexes bind to, but the cell still requires the receptor to form that complex. The presence of a hormone in the blood without matching receptors in the cell will not cause a response.
Step-by-Step Solution:
1. Recognize that hormones are broadcast signals that travel everywhere in the bloodstream.2. Understand that only target cells that have the correct receptor can detect and respond to a hormone.3. If a cell lacks the specific receptor, the hormone will not bind and no signal will be transmitted inside the cell.4. A hormone response element is a segment of DNA that a receptor hormone complex may bind to, but without the receptor there is no specific recognition.5. Simply having a hormone like adrenocorticotropic hormone in the blood does not force every cell to respond; only cells with its receptor will react.6. Therefore, the factor that allows a cell to respond to a hormone is the presence of the appropriate hormone receptor.
Verification / Alternative check:
Endocrinology texts describe how different tissues express different sets of hormone receptors. For example, insulin acts mainly on liver, muscle, and fat cells because they possess insulin receptors. Thyroid hormone affects many tissues, but the extent of response depends on receptor levels in those tissues. Experiments that artificially add receptors to cells can make new tissues respond to a hormone that previously had no effect, which demonstrates that the receptor is the determining factor. Conversely, loss or mutation of receptors can cause hormone resistance even when hormone levels are normal.
Why Other Options Are Wrong:
Option B, hormone response element without any receptor, is wrong because DNA sequences alone cannot sense hormones; the receptor hormone complex is needed to bind there. Option C, adrenocorticotropic hormone present in the blood, is incorrect because the question is not about a specific hormone but about the general mechanism that allows a cell to respond. Option D, random diffusion of hormones through all cells, is misleading because hormones do diffuse through tissues, but their effects are specific and depend on receptor binding, not on random passage through cells.
Common Pitfalls:
Students sometimes think that once a hormone is in the blood, it will automatically act on every cell, which is not true. Another pitfall is confusing response elements in DNA with receptors on or in the cell, forgetting that the receptor is the key recognition molecule. To avoid these issues, remember the simple rule that target cells are defined by the receptors they express, and hormones are like keys that fit only certain locks on these cells.
Final Answer:
A cell is able to respond to a particular hormone because of the presence of a specific hormone receptor on or in that cell that can bind the hormone and start a signal.
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