Use the following information to answer the question. In order to test how sea urchin sperm bind to eggs, scientists isolated the egg receptor protein

that binds to the sperm acrosomal protein called bindin. Plastic beads were coated with egg receptor for bindin (ERB1) from eggs of the sea urchin Strongylocentrotus purpuratus, and then the beads mixed with sperm from S. purpuratus or from the related species, S. franciscanus. The researchers counted how many sperm were bound to each bead. The results are shown in the graph below. Treatments:

A: S. purpuratus sperm mixed with S. purpuratus ERB1 beads

B: S. purpuratus sperm mixed with beads containing no ERB1 protein

C: S. franciscanus sperm mixed with S. purpuratus ERB1 beads

D: S. franciscanus sperm mixed with beads containing no ERB1 protein

Based on the data in the graph, which of the following conclusions is supported?

#Question id: 1224

#Unit 4. Cell Communication and Cell Signaling

Put the steps of the process of signal transduction in the order they occur.

1. A conformational change in the signal-receptor complex activates an enzyme.

2. Protein kinases are activated.

3. A signal molecule binds to a receptor.

4. Target proteins are phosphorylated.

5. Second messenger molecules are released.

#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