38) Cells can regulate their responsiveness to chemical messengers. For example,
ID: 3509322 • Letter: 3
Question
38) Cells can regulate their responsiveness to chemical messengers. For example, a cell that ‘wanted’ to decrease its physiological response evoked by a chemical messenger could theoretically do so by which mechanism(s)? Assume all these are possible, which one could produce the desired effect. Choose ALL that apply. (2.5 points)
a) Degrade a lipophilic first messenger more slowly.
b) Downregulate the number of receptors for the chemical messenger.
c) Phosphorylate a molecule in the intracellular signaling pathway to decrease its activity.
d) Phosphorylate the receptor so that it has a decreased affinity for the chemical messenger.
e) Remove a second messenger more quickly.
Explanation / Answer
Lets understand a few terms first.
1. First messengers are extracellular factors, like hormones or neurotransmitters, which are the extracellular signaling molecules.
2. Second messengers are molecules released in the cell in response to first messengers, which are intracellular sigmaling molecules. Examples: cGMP, cAMP, Inositol triphosphate, diacylgycerol and calcium.
In this question, the desired effect is to DECREASE the physiological response by a chemical messenger.
Amongst the given options the following explanations are likely:
a) Degrade a lipophilic first messenger more slowly.
If the first messenger is degraded slowly, it will lead to a prolonged action of the first messenger. Hence this option will not decrease the physiological response of the cell, instead it may lead to an increased or continued response.
b) Downregulate the number of receptors for the chemical messenger.
By downregulating the number of receptors for the chemical messenger, the responsiveness of the cell to the first messenger is decreased, ultimatley, leading to a decreased physiological response of the cell.
c) Phosphorylate a molecule in the intracellular signaling pathway to decrease its activity.
By phosphorylation of a molecule in the pathway, signaling increases, hence activity increases. Hence this option will not decrease the physiological response of the cell.
d) Phosphorylate the receptor so that it has a decreased affinity for the chemical messenger.
Phosphorylation of receptors changes their shape, so affinity decreases and so it is desensitized. Hence this option will decrease the physiological response of the cell.
e) Remove a second messenger more quickly.
ASSUMING that removing the second messenger is possible, the desired action can be decreased. Hence this option will decrease the physiological response of the cell. (However, cAMP cannot be removed as such. This answer is based on assumption)
ANSWERS: B, D, E
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