BSI Lecture 19 Adaptation/Desensitization Flashcards

1
Q

_____________ is a GPR with a bound light-sensitive messenger.

A

Rhodopsin

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2
Q

Rhodopsin can be excited by as little as one photon and cause the activation of the heterotrimeric G-protein _______.

A

Transducin (Gt) only found in photoreceptors

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3
Q

Adaptation: The effector is a cGMP phosphodiesterase, does it increase or decrease cGMP?

A

Decrease, which in turn closes an ion channel

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4
Q

Adaptation: From 1 rhodopsin to 500 transducins; 10^5 molecules of cGMP, this is an example of ___________

A

Amplification

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5
Q

________ and ______ is a general physiological term used to describe various mechanisms necessary to cope with stimulilsignals that vary widely in strength.

A

Adaptation; desensitization

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6
Q

__________ tends to refer more to actual changes in receptor function whereas __________ can include altered behavior

A

Desensitization, adaption

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7
Q

Adaptation is seen frequently in signal pathways that respond to _______ signals and ______

A

chemical; light

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8
Q

T or F? Desensitization allows cells to respond regardless of “background” levels of stimulation.

A

False, adaption not desensitization

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9
Q

_________ can respond to a few photons on a moonless night or reduce amplification so they still respond in bright sunshine; _______ intracellular Ca2+/Ca2+-dependent kinases causes this negative feedback.

A

Photoreceptors, increased

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10
Q

T or F? Ionotropic receptors can adapt or desensitze to repeated agonist by a “slow” confirmation change in the receptor resulting in abnormally tight binding of the agonist w/o opening the channel.

A

True

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11
Q

What are the 2 principal types of receptor desensitization?

A

Heterologous, homologous

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12
Q

________ desensitization is negative feedback within the same pathway (turning off GPR)

A

Homologous

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13
Q

________ involves negative feedback affecting GPR initiating a different pathway.

A

Heterologous

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14
Q

T or F? Homologous desensitization involves phosphorylation of the GPR by GRK’s.

A

True

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15
Q

T or F? Homologous desensitization involves specific phosphorylation of the GPR but by different serine/threonine kinases at different serine and/or threonine residues.

A

False, heterologous desensitization

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16
Q

_______ desensitization results in loss of G-protein coupling or removal of receptors entirely by endocytosis.

A

Homologous

17
Q

_______ desensitization results in reduced G-protein coupling.

A

Heterologous

18
Q

How is heterologous desensitization reversed?

A

By phosphatases, which restores G-protein coupling

19
Q

T or F? Heterologous feedback mechanism often involves cAMP-dependant protein kinase (PKA) or can be PKC-mediated.

A

True

20
Q

Ligand-bound form of the GPR is phosphorylated at specific serine/threonine residues and this ________ coupling to the G-protein so it can not be activated.

A

decrease

21
Q

______ desensitization involves GRK phosphorylating the GPR which then facilitates arrestin binding which makes the GPR unable to activate its G-protein (uncoupled)

A

Homologous

22
Q

______ desensitization can trigger internalization by endocytosis, the GPR can then be degraded or recycled

A

Homologous

23
Q

T or F? Arrestin binding can activate MAPK cascade by acting as an “adapter” so recruiting the various kinases to the membrane.

A

True. ( Has been most studied for teh Beta2-adrenergic receptor, its GRK is known as BetaARK and its arrestin is Beta-Arrestin)

24
Q

T or F? G-protein effector can be switch from one type of G-protien to another by being phosphorylated.

A

True. This in turn can change the response (ie switching Gs (increase cAMP) to Gi (reducing cAMP))

25
Q

T or F? GPR’s under constant agonist application will have a constant increase cell response.

A

False, there is an initial rapid decrease in response.

26
Q

T or F? Initial response to constant agonist involves no change in receptor density.

A

True

27
Q

Response to constant agonist slowly declines further due to a ______ in _____ _______

A

decrease ; receptor density (this is due to internalization)