When a person drinks alcohol, the rate of urination increases. Which of the following best accounts for the increase in urination above normal rates?

TLS Online TPP Program

#Question id: 14685

#Unit 4. Cell Communication and Cell Signaling

In dark-adapted rod cells, a high level of cGMP keeps cGMP-gated nonselective cation channels open, leading to hyperpolarization of the plasma membrane and neurotransmitter release. 

B - Light absorption generates activated rhodopsin, R*, which binds inactive, GDP-bound Gαt protein and mediates the exchange of GDP for GTP . 

C- The free Gαt∙GTP activates PDE by binding to its inhibitory γ subunits and dissociating them from the catalytic α and β subunits . Relieved of their inhibition, the α and β subunits of PDE hydrolyze GMP to cGMP . 

D- The resulting decrease in cytosolic cGMP leads to dissociation of cGMP from the cation channels in the plasma membrane and the closing of those channels . 

E- The membrane then becomes transiently hyperpolarized, and neurotransmitter release is reduced. 

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#Question id: 14686

#Unit 4. Cell Communication and Cell Signaling

This member of the AKAP family, designated mAKAP, anchors both PDE and the regulatory subunit  of PKA to the nuclear membrane, maintaining them in a negative feedback loop that provides close local control of the ATP level and PKA activity.

B- The basal level of PDE activity in the presence of hormone (resting state) keeps cAMP levels below those necessary for PKA activation. 

C- Activation of β-adrenergic receptors causes an increase in cAMP to a level in excess of that which can be degraded by PDE. 

D- The resulting binding of cAMP to the R subunits of PKA releases the active catalytic (C) subunits into the cytosol. Some C subunits enter the nucleus, where they phosphorylate and thus activate certain transcription factors . Other C subunits phosphorylate PDE, stimulating its catalytic activity.

E-  Active PDE hydrolyzes cAMP, thereby driving cAMP levels back to basal levels and causing re-formation of the inactive PKA C-R complex. Subsequent de-phosphorylation of PDE returns the complex to the resting state.

TLS Online TPP Program

#Question id: 14738

#Unit 4. Cell Communication and Cell Signaling

Choose correct statements about Muscarinic receptors;

a. An acetylcholine analog, In activated condition, these receptors slow the rate of heart muscle contraction.

b .This type of receptor is coupled to a Gαi protein, and ligand binding leads to the opening of an associated K+ channel.

c .The subsequent influx of K+ ions from the cytosol causes an increase in the magnitude of the usual inside-negative potential across the plasma membrane that lasts for several seconds. 

TLS Online TPP Program

#Question id: 14739

#Unit 4. Cell Communication and Cell Signaling

In heart muscle, activation series of the muscarinic acetylcholine receptor its effector K+ channel via the Gβγ subunit of a Gi protein.

a. Binding of acetylcholine triggers activation of the Gαi subunit and its dissociation from the Gβγ subunit in the usual way. 

b. The released Gβγ subunit (rather than Gαi∙GTP) binds to and opens the associated effector protein, a K+ channel. 

b. The increase in K+ permeability hyperpolarizes the membrane, which reduces the frequency of heart muscle contraction. 

d. Activation is terminated when the GTP bound to Gαi is hydrolyzed (by a GAP enzyme that is an intrinsic part of the Gαi subunit) to GDP and Gαi∙GDP recombines with Gβγ.

TLS Online TPP Program

#Question id: 14740

#Unit 4. Cell Communication and Cell Signaling

Rod cells sense light with the aid of a light-sensitive GPCR known as rhodopsin; choose incorrect statements

a. Rhodopsin consists of the protein opsin, which has the usual seven–transmembrane segment GPCR structure, covalently linked to a light-absorbing pigment called retinal. 

b. Rhodopsin, found only in rod cells, is localized to the thousand or so flattened membrane disks that make up the inner segment of each of these rod-shaped cells.

c. A human rod cell contains about 4 × 10⁷ molecules of rhodopsin. 

d. The heterotrimeric G protein coupled to rhodopsin, called transducin (Gt), contains a Gα unit referred to as Gαt; like rhodopsin, Gαt is found only in rod cells.

TLS Online TPP Program

#Question id: 27107

#Unit 4. Cell Communication and Cell Signaling

Which of the following receptors is not a signalling receptor?