Download Chapter 5 Quantitative and Thought Questions 5.1 Patient A`s drug

Chapter 5
Quantitative and Thought Questions
5.1 Patient A’s drug very likely acts to block phospholipase A 2 , whereas patient B’s drug blocks
lipoxygenase (see Figure 5.12).
5.2 The chronic loss of exposure of the heart’s receptors to norepinephrine causes an up-regulation of
this receptor type (i.e., more receptors in the heart for norepinephrine). The drug, being an agonist of
norepinephrine (i.e., able to bind to norepinephrine’s receptors and activate them) is now more
effective because there are more receptors for it to combine with.
5.3 None. You are told that all six responses are mediated by the cAMP system; consequently, blockage
of any of the steps listed in the question would eliminate all six of the responses. This is because the
cascade for all six responses is identical from the receptor through the formation of cAMP and activation
of cAMP-dependent protein kinase. Therefore, the drug must be acting at a point beyond this kinase
(e.g., at the level of the phosphorylated protein mediating this response).
5.4 Not in most cells, because there are other physiological mechanisms by which signals impinging on
the cell can increase cytosolic Ca 2 1 concentration. These include (a) second-messenger-induced
release of Ca 2 1 from the endoplasmic reticulum and (b) voltage-sensitive Ca 2 1 channels.
5.5 Intracellular second messengers do not disappear immediately upon removal of a first messenger.
Instead, some second messengers (such as cAMP) may linger inside the cell for seconds, minutes, or
even longer after the first messenger is gone.
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