BIOL 2021 Lecture Notes - Lecture 12: Lysosome, Signal Transduction, G Protein–Coupled Receptor
13 May 2018
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o Fig 15-18D effects of negative feedback: long time delay causes
oscillations.
• Adaptation (830-831)
• Fig 15-20 adaptation mechanism: how do you change your response, change
the sensitivity?
o Adaptation = desensitization (less sensitive to the signal, even if signal is
there, will tamp down the response) = change detector. In responding to
many types of stimuli, cells and organisms are able to detect the same
percentage of change in a signal over a wide range of stimulus strengths.
The target cells accomplish this through a reversible process of
adaptation, or desensitization, whereby a prolonged exposure to a
stimulus decreases the cells’ response to that level of stimulus.
o General mechanism = negative feedback with short delay. The underlying
mechanism is negative feedback that operates with a short delay: a strong
response modifies the signaling machinery involved, such that the
machinery resets itself to become less responsive to the same level of
signal.
o Specific mechanisms for desensitization:
o 1) Temporary receptor sequestration = removal from PM (endocytosis),
taking off from membrane (inactivation of the receptors by temporary
sequestration of the receptors in endosomes).
o 2) down regulation of receptor = destruction of receptor, taken into the
lysosomes (signal-induced receptor endocytosis leads to the destruction
of the receptors in lysosomes, a process referred to as receptor down-
regulation).
o 3) receptor inactivation (ex: phosphorylation). You just inactivate it, no
destruction or removal.
o 4) inactivation of signaling protein downstream of receptor.
o 5) producing inhibitor downstream.
o Adaptation can also occur at sites downstream of the receptors, either by
a change in intracellular signaling proteins involved in transducing the
extracellular signal or by the production of an inhibitor protein that blocks
the signal transduction process.
o These are quantitative responses by the cell. Not a yes or no thing.
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