A proposed pathway for the action of E.coli chaperonins  are groEL and groES.groEL exist in trans and cis structure transferring with its bound ATP now become the cis ring once the groES  bound to it ATP hydrolysis takes place and improperly folded protein get properly folded, total number of  ATP molecules are required to per folding cycle;

#Question id: 1225

#Unit 4. Cell Communication and Cell Signaling

The dissociation constant Kd for a receptor-ligand complex is

a. a measure of the affinity of the receptor for the ligand.

b. the concentration of the ligand at which half of the receptors contain bound ligand.

c. a measure of the time it takes for a ligand to be converted to a product.

d. equal to koff/kon 

#Question id: 1226

#Unit 4. Cell Communication and Cell Signaling

GTPase switch proteins

a. are active when bound to GDP but inactive when bound to GTP.

b. are active when bound to GTP but inactive when bound to GDP.

c. are converted from the inactive to active state by a guanine nucleotide exchange factor (GEF).

d. synthesizes GTP from GDP.

#Question id: 1227

#Unit 4. Cell Communication and Cell Signaling

Which of the following is a mechanism for down regulation of signaling from G protein-coupled receptors?

a. a change in the Kd of the receptor-hormone complex

b. proteolysis of the Gα subunit                     

c. hydrolysis of cAMP to 5´-AMP

d. dephosphorylation of adenylyl cyclase

#Question id: 1228

#Unit 4. Cell Communication and Cell Signaling

Place the events that follow the binding of a ligand to a G protein-coupled receptor that acts on adenylyl cyclase in the correct order:

a. GTP is hydrolyzed to GDP.           

b. GDP is displaced from Gα.           

c. the Gα-GTP complex dissociates from the Gβγcomplex.  

d. GTP is bound to Gα. 

#Question id: 1229

#Unit 4. Cell Communication and Cell Signaling

Which of the following events occur(s) during light activation of the rhodopsin receptor?

a. 11-cis-retinal is converted to all-trans-retinal

b. activation of the trimeric G protein, transducin

c. activation of cGMP phosphodiesterase

d. opening of the cGMP-gated ion channel

#Question id: 1230

#Unit 4. Cell Communication and Cell Signaling

Which of the following events occur(s) following the binding of a ligand to a G protein–coupled receptor that triggers release of Ca2+?

a. activation of protein kinase A by IP3

b. phospholipase cleavage of PIP2 to IP3 and DAG

c. release of DAG into the cytosol

d. IP3-mediated opening of Ca2+ channels in the ER membrane